DEVELOPMENTAL REVIEW ARTICLE NO.
18, 86–123 (1998)
DR970445
The Development of Efficient Inhibition: Evidence from Directed-Forgetting Tasks Steffen Pope Wilson Eastern Kentucky University
and Katherine Kipp University of Georgia The purposes of this paper are (1) to end the confusion over the mechanisms producing directed-forgetting effects in the three methods of cuing items in directedforgetting tasks, (2) to highlight the role of inhibition in blocked and ‘‘only’’ cued directed-forgetting tasks, and (3) to review and reinterpret the developmental directed-forgetting literature within an inhibition framework. We argue that item-byitem cued directed-forgetting tasks manipulate selective rehearsal to produce greater recall of to-be-remembered (TBR) than to-be-forgotten (TBF) items. In contrast, both blocked and ‘‘only’’ cued directed-forgetting tasks manipulate retrieval inhibition, a form of cognitive inhibition, to produce the suppression of TBF items. The current developmental directed-forgetting literature is reviewed and reinterpreted in light of this framework. It is concluded that in item-by-item tasks children can produce directed-forgetting effects using selective rehearsal by second grade. In blocked and ‘‘only’’ cued directed-forgetting tasks children can produce directedforgetting effects as early as third grade in some instances, but usually not until fifth grade. Future directions for research on cognitive inhibition, especially its role in the investigation of repressed memories, are also discussed. 1998 Academic Press
Several contemporary theories suggest that the gating of irrelevant information from the information processing stream is an important component of efficient cognition. Specifically, these theories have proposed that a porKatherine Kipp’s earlier work is published under the name Katherine Kipp Harnishfeger. The authors thank Rich Marsh for comments on earlier drafts of this manuscript. A portion of this manuscript was submitted in partial fulfilment of a Doctorate of Philosophy degree awarded to the first author. Portions of this review were presented at the Conference on Human Development (Birmingham, AL, 1996). This research was supported by a grant to the second author from the National Science Foundation (SBR-9408323). Address correspondence and reprint requests to Steffen Wilson, Department of Psychology, Eastern Kentucky University, Richmond, KY, 40475. E-mail:
[email protected] or Katherine Kipp, Department of Psychology, University of Georgia, Athens, GA 30602. E-mail:
[email protected]. 86 0273-2297/98 $25.00
Copyright 1998 by Academic Press All rights of reproduction in any form reserved.
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tion of the improvements in cognition seen with development is a product of increasingly efficient gating mechanisms (Bjorklund & Harnishfeger, 1990; Brainerd & Reyna, 1993; Dempster, 1993; Harnishfeger & Bjorklund, 1993). In parallel, it has also been proposed that portions of the decrements in cognition found in the aging process are due to increasingly inefficient mechanisms for gating irrelevant information (Hasher & Zacks, 1988; Stoltzfus, Hasher, & Zacks, 1996). The inefficient inhibition hypothesis (Bjorklund & Harnishfeger, 1990; Harnishfeger, 1995; Harnishfeger & Bjorklund, 1993) is an extension of the limited mental resources model (Case, 1985; Case, Kurland, & Goldberg, 1982). The limited mental resources model proposes that mental capacity is composed of processing space and storage space and that the total amount of mental resources available to perform cognitive tasks remains stable throughout childhood. The increase in the efficiency of cognition seen during childhood is due to increasingly efficient processing of cognitive tasks. As processing becomes more efficient, less processing space is needed to complete a cognitive task. This allows the processing space, which was previously needed for task completion, to be released and used for subsequent processing or for storage (Case, 1985; Case et al., 1982). Cognitive inhibition refers to the suppression of previously activated cognitive contents or cognitive processes (Bjorklund & Harnishfeger, 1990; Harnishfeger, 1995; Harnishfeger & Bjorklund, 1993). Individuals who are efficient inhibitors are able to expel from working memory previously activated information that is not relevant to task performance. This leaves less information in working memory to be processed, decreasing the amount of processing space that is needed to complete a task, and makes a greater portion of the limited mental capacity available to relevant processing or storage. Although in some instances an individual may not be aware of his or her inhibitory processes (i.e., lexical decision tasks), cognitive inhibition is an active process. Efficient inhibitory ability develops during childhood, with some inhibitory skills becoming efficient as late as adolescence (Harnishfeger, 1995). It is a basic-level processing mechanism that is thought to develop as a byproduct of frontal lobe maturation (Bjorklund & Harnishfeger, 1995; Dempster, 1993). Young children are relatively inefficient inhibitors. That is, they are not able to inhibit information that has become activated in working memory and that is not necessary for current task performance. With age, children become increasingly able to inhibit irrelevant information. Less information remains in working memory, which in turn facilitates cognitive efficiency. It is currently argued that there are several domains of inhibition. Dempster (1993) suggests that inhibitory development occurs first within motor, then perceptual, and finally within linguistic domains. Harnishfeger (1995) has proposed two ways of classifying inhibition. First, a distinction between
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cognitive and behavioral inhibition can be made, with behavioral inhibition controlling motor movements and developing before cognitive inhibition, which acts on mental processes. Second, she proposed a distinction between unintentional and intentional inhibitory processes. Intentional inhibition occurs when an individual decides that an item is irrelevant and suppresses its activation. Unintentional inhibition occurs when an irrelevant item is activated automatically in conjunction with relevant information and is suppressed by the cognitive system prior to conscious awareness. An alternative view that inhibition is a single process that is early developing and is applied to many cognitive processes has also begun to receive support. According to this view, efficient inhibitory ability can be applied to all tasks that fall within the processing capabilities of the child (Tipper, Bourque, Anderson, & Brehaut, 1989; Tipper & McLaren, 1990). The single process view proposes that a child can inhibit within tasks that do not overly tax the child’s processing capacity. For example, Kipp and Pope (1996) found that, by second grade, children are efficient inhibitors within a picture-naming task, a task at which even young children can excel. The single process view explains developmental improvements in inhibitory efficiency as a by-product of the child’s increasing cognitive efficiency. That is, the child is able to perform more complex cognitive tasks with age, and the child’s inhibitory abilities are more evident in a wider variety of situations. It is important to distinguish cognitive inhibition from a related cognitive process, resistance to interference (Brainerd & Reyna, 1993). Inefficient inhibition theory and resistance to interference theory explain two different aspects of cognitive development. However, because they are very similar in nature and thought to be controlled by similar neurological mechanisms (Dempster, 1993), they are easily confused. Interference refers to decreases in processing efficiency by multiple sources of information competing to enter working memory (Brainerd & Reyna, 1993; Dempster, 1993). Similar to cognitive inhibition, resistance to interference is a gating mechanism that develops with age and promotes the ability to ignore irrelevant information. However, resistance to interference differs from cognitive inhibition is several important ways. Resistance to interference does not interact with the concept of limited mental resources. With age, children become less sensitive to potentially interfering information. Therefore, with age, potentially interfering information does not compete with relevant information in cognitive processing. Unlike cognitive inhibition, this is thought to be a passive process. However, similar to cognitive inhibition, resistance to interference is thought to be a product of frontal lobe development (Dempster, 1993). The most significant difference between efficient inhibition and resistance to interference is the location of competition for processing space. Inhibited items are first encoded into working memory, determined to be irrelevant,
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and are then expelled from working memory. Inhibited items are not available at recall, but because they were encoded, they should be available in recognition memory equally as well as items produced at recall. Interference from an irrelevant item is resisted before the item enters into working memory. Therefore, information that has resisted interference has never been encoded into working memory. This information is not available in recognition memory. The availability of inhibited items in recognition memory does not necessarily indicate that the strength of the inhibited traces are equivalent to the traces that have not been inhibited. Recognition can be based upon either conscious recollection or unconscious familiarity (Mandler, 1980). The quality of the encoded trace of an inhibited item can range from detailed to vague. The processing stage at which an item is inhibited following encoding is also not clear. The retrieval inhibition mechanism may work simultaneously with encoding, between encoding and retrieval, or at retrieval (cf. MacLeod, 1989). Future work examining the inhibition mechanism should address this issue. Inhibition is also distinguished from forgetting. Because inhibited items must have been initially encoded, been deemed irrelevant, and then been expelled from working memory, they should be available in some form in memory. An inhibited item is not a forgotten item, but rather an item whose activation has been suppressed. Although cognitive inhibition itself is not a forgetting phenomenon, the developmental trends in forgetting (Brainerd, Reyna, Howe, & Kingma, 1990; Cassel & Bjorklund, 1995; Howe & Brainerd, 1989) should affect an inhibited memory trace. That is, an inhibited memory trace probably decays more quickly at young ages and with time and interference, just as a memory trace that had not been inhibited does. There is a growing body of research on the development of efficient inhibition. Most of the investigations of cognitive inhibition and its development have focused on ‘‘unintentional’’ inhibition as opposed to ‘‘intentional’’ inhibition. Unintentional inhibition occurs when irrelevant items are automatically activated along with relevant items. The individual must suppress the automatically activated irrelevant items in order to successfully process the relevant items. This type of inhibition is ‘‘unintentional’’ because the individual is usually not aware that he or she is inhibiting certain items. An example of intentional inhibition is the suppression of the irrelevant meanings of polysemous words in language processing (e.g., suppressing the animal meaning of the word ‘‘bat’’ when reading a text about baseball). Intentional inhibition occurs when an individual consciously decides that an item is irrelevant and suppresses its activation. An example of intentional inhibition is the suppression of words that are cued as TBF in a directed-forgetting task.
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ABBREVIATED REVIEW OF THE UNINTENTIONAL INHIBITION LITERATURE The following is a brief review of the research investigating unintentional inhibition. In each study, an item is automatically activated and must be inhibited to complete the task successfully. The ability to inhibit these automatically retrieved irrelevant items develops during the elementary school years in each study. The negative priming version of the Stroop task has been used to investigate the role of inhibition in the development of selective attention of elementary age children (Tipper et al., 1989). In the Stroop task, participants are presented with a series of color words that are printed in colored ink (e.g., the word RED printed in blue letters). The participant is asked to name the colored ink of each word in the series while not naming the color word. The color word is automatically activated because the individual reads the word when determining the color of ink. The automatic activation of the color word hinders the naming of the colored ink. In the negative priming version of this task, the color of ink on one trial is the same color as the color word from the previous trial. The color word is activated when the participant automatically reads the word while naming the colored ink. On the following trial, the color word must be released from inhibition because it is the same as the ink color on the previous trial. Releasing each color word from inhibition in order to name the current color of ink should increase the naming latency to name the series of items in a negative priming series as compared to a standard stroop control condition. This increase in naming latency for efficient inhibitors in the negative priming condition as compared to the stroop condition is referred to as the ‘‘negative priming effect.’’ Tipper and his colleagues (Tipper et al., 1989) examined negative priming in second grade children and adults. They found negative priming in adults, but not in children. This was interpreted as a product of more efficient inhibitory ability in adults as compared to children. Diamond and her colleagues (Diamond, Cruttenden, & Neiderman, 1994) reported evidence that infants’ errors on the A not B task may not be due exclusively to a memory failure as previously suggested (Cummings & Bjork, 1983a, 1983b; Goldman-Rakic, 1987). Instead, A not B errors could be due to inefficient inhibition of the previously activated and reinforced hiding position, in addition to possible errors in memory (Diamond et al., 1994). In the A not B task, an object is shown to an infant and then placed in one of two or more hiding places while the infant watches. Following a brief delay, infants 7.5 to 12 months old will correctly retrieve the hidden object following a single hiding trial. However, if the object is then re-hidden in a second hiding place, infants have difficulty retrieving the object (the A not B error). Diamond and her colleagues found that infants made a disproportionate number of incorrect reaches to the previously reinforced hiding
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place. This sometimes occurred while the child was looking at the correct hiding place (Diamond, 1991a). Diamond and her colleagues speculated that the infant was automatically retrieving the previously correct hiding place and could not inhibit the tendency to reach towards it. Therefore, to successfully perform the A not B task an infant must not only remember the correct hiding place, but she must also inhibit the tendency to reach to the automatically activated previously correct hiding place. Cognitive inhibition is also thought to play a role in the retrieval of superordinate category names (Clark & Johnson, 1994). Children produce basic level category names of items earlier in development than superordinate level category names (Rosch, Mervis, Gray, Johnson, & Boyes-Braem, 1976). Johnson and her colleagues propose that this difference in the types of category names a child produces is not a product of a knowledge or comprehension difference. Instead, it is a product of a production difference. That is, they believe that young children understand the meaning of superordinate category labels, but that the basic level label of an object is automatically activated and must be inhibited for the child to retrieve and produce the superordinate level label. Because young children cannot inhibit the automatically activated basic level label, they are less likely to produce the superordinate level label when it is requested. To test this theory, Clark and Johnson (1994) compared comprehension differences in superordinate and basic level category names in 5- and 7-year-old children. Children were shown pictures ?’’. of common objects and asked questions in the form of ‘‘Is this Each child was asked first to recognize the basic level name for an object. Then the child was asked to recognize the superordinate level name for an object. It was found that both the 5- and 7-year-old children comprehend (or recognize) basic level and superordinate level object names equally well. The children were then asked to produce the objects’ ‘‘own’’ (basic level) name and the objects’ ‘‘group’’ (superordinate level) name. The younger children were significantly less likely to produce the objects’ ‘‘group’’ name than the objects’ ‘‘own’’ name. The older children produced both the basic and superordinate level names. These results confirm Clark and Johnson’s prediction that 5- and 7-year-old children understand both basic and superordinate level item names equally well. These results are consistent with the conclusion that younger children are not able to inhibit the automatically activated basic-level item name. The basic-level name remains activated and impedes the production of the superordinate level name. In an investigation of the role of inhibition in memory, children in nursery school, kindergarten, third and sixth grade were presented target words to be remembered, along with a cue word (Harnishfeger & Bjorklund, 1993). The cue word was either categorically, functionally, or acoustically related to the target word. At recall, children were presented the cue word and asked to recall the target word. The number of intrusions in recall was measured to determine the effects of children’s inability to keep irrelevant information
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from interfering with recall. For younger children, more intrusions were automatically activated and produced at recall than for older children. In addition, the younger children activated and produced intrusions that were not functionally, acoustically, or categorically related to the cue word. The younger children’s recall pattern was consistent with inefficient inhibitory ability. The older children produced fewer intrusions, and the intrusions were more likely to be categorically, functionally, or acoustically related to the cue word. The older children’s pattern of results was more consistent with strategic guessing than inhibitory failure. A free recall test of items was also presented to children in kindergarten, second and fourth grade (Harnishfeger & Bjorklund, 1993). One list of words was presented in two different orders. One ordering of the words highlighted their categorical relationships. The second ordering of the words highlighted the acoustic relationships between the items. It was again found that the younger children made more intrusions and more inappropriate intrusions than the older children. That is, the younger children made intrusions that were not related to the ordering of the list, while the older children made intrusions that were related to the ordering of the list. It was concluded from these studies that young children retain irrelevant information in working memory, and that this irrelevant information hinders memory. REVIEW OF THE INTENTIONAL INHIBITION LITERATURE The literature on intentional inhibition is limited. The only research investigating intentional inhibition is a study investigating the development of efficient inhibition using a picture-naming task (Kipp & Pope, 1996) and studies using the directed-forgetting task. It is important that we correctly interpret results from directed-forgetting research so that this method can be used to investigate the development and operating characteristics of intentional cognitive inhibition. The Picture-Naming Task The role of efficient inhibition in directed speech (Kipp & Pope, 1996) was investigated by Kipp and her colleagues in a picture-naming task. Children in kindergarten, second and fourth grades and college-age adults were presented a picture-naming task in which they were asked to name all of the items in a complex picture while not naming (i.e., inhibiting) a target item. The target item would have to be inhibited because it becomes activated when the individual looks at the picture. This naming trial was immediately followed by a second trial in which the children and adults were told to continue naming the items in the picture and that they could now name the target item. Individuals who are efficient inhibitors should name significantly fewer items in the first naming trial than in the second naming trial. The difference in items named in both trials should be smaller in individuals who are inefficient inhibitors as compared to efficient inhibitors. Item naming in the inhibition
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condition was compared to a control condition in which participants were asked to name all of the items in the picture in both consecutive naming trials. By second grade, children named significantly more items in the second naming trial than in the first naming trial in the inhibition condition. This difference in the number of items named continued to increase with age. There were no reliable differences at any age in the number of items named in both trials in the control condition. The results of this experiment are consistent with the interpretation that children are efficient inhibitors in directed speech by second grade. The Directed-Forgetting Task In a directed-forgetting task, items are cued as either to-be-forgotten (TBF) or to-be-remembered (TBR). When both item types are requested at recall, efficient directed-forgetting is found when significantly more TBR items are recalled than TBF items. Directed-forgetting effects are also found when the TBF items that were presented at item learning, but not requested at recall, do not hinder the recall of the TBR items. If cognitive inhibition plays a role in the directed-forgetting task, a particular pattern of of directed-forgetting performance should be found. The difference in young children’s recall of TBR and TBF items should be smaller than the difference found in older children and adult’s TBF and TBR item recall. This would occur because young children’s inefficient inhibitory skills prevent them from inhibiting the TBF items as well as do the older children and adults at recall. However, at all ages, all of the items presented, both those items inhibited and those items not inhibited, should be available in recognition memory because all of the items were encoded.1 The predominant explanation of directed-forgetting effects in the literature, however, has not been an inhibition explanation. Instead, directed-forgetting effects have been interpreted as a product of ‘‘selective rehearsal’’ (e.g., Bjork, 1970, 1972; Bjork & Woodward, 1973; Bruce & Papay, 1970; Davis & Okada, 1971; Geiselman, 1974; Gross, Barresi, & Smith, 1970; MacLeod, 1975; Webb, Stock, Kulhavy, Haygood, Zulu, & Robinson, 1990). This explanation proposes that TBR items are rehearsed during list presentation, while the TBF items are not rehearsed. Differential item rehearsal produces differential encoding of the TBR and the TBF items. The TBR items are rehearsed and encoded during item presentation, and the TBF items are 1 Equivalent recognition memory may not indicate similar trace representations of inhibited and uninhibited items. All of the currently reported directed-forgetting tasks that have investigated trace quality have used a recognition task to determine trace quality. From the currently reported data, it is impossible to know exactly the quality of the traces that were not recalled but that were recognized. An alternate method of testing recognition in directed-forgetting tasks, such as remember-know judgments or process dissociations should be used in future research.
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not rehearsed and not encoded during item presentation. Directed-forgetting effects, or greater TBR than TBF item recall, is therefore proposed to be a product of greater encoding of the TBR than the TBF items. Results inconsistent with the selective rehearsal interpretation have been found in the directed-forgetting literature. For example, Bray, Justice, and Zahm (1983) reported mature directed-forgetting performance in fifth-grade children who were not able to selectively rehearse in an adultlike manner. If selective rehearsal is the process responsible for efficient directed-forgetting, directed-forgetting effects should not be seen until selective rehearsal becomes mature. In addition, equal recognition of the TBR and TBF items, although the TBF items were not recalled, has also been reported (Harnishfeger & Pope, 1996). Equal recognition, but differential recall, of both item types indicates that all of the items were encoded in memory, counter to the selective rehearsal hypothesis. An inhibition explanation of directed-forgetting effects has been offered in the directed-forgetting literature to explain these inconsistent results (Bjork & Geiselman, 1978; Block, 1971; Elmes, Adams, & Roediger 1970; Geiselman, Bjork, & Fishman, 1983; Geiselman & Bagheri, 1985; Reitman, Malin, Bjork, & Higman, 1973; Woodward & Bjork, 1971). However, there continues to be confusion over the correct interpretation of directed-forgetting effects, in part, because there are several methods of cuing items as TBR and TBF and all are called directed-forgetting. Although these methods do not produce directed-forgetting effects by the same mechanism, they have been considered interchangeable. In addition, the method of cuing is not highlighted in studies using the directed-forgetting task. One must examine the method section of an empirical paper to determine the method of cuing so that the correct interpretation of the mechanism producing greater TBR than TBF recall can be made. This paper will review the developmental directed-forgetting literature in light of recently proposed models featuring the role of inhibition in cognition and propose directions for future research in this area. In the following section of this paper, the three methods of cuing items as TBR and TBF are reviewed, a framework for interpreting directed-forgetting effects in each method is outlined, and some examples of the problems encountered with methodological confusions are described. In the second section, the results of developmental directed-forgetting research are reinterpreted within an inhibition framework. This is important to do because the current directedforgetting studies will be used as a base for future directed-forgetting investigations. In the final section, directions for future research on cognitive inhibition and its development are proposed. DIRECTED-FORGETTING METHODS There are three methods of cuing items as TBR and TBF in a directedforgetting task that have been reported in the directed-forgetting literature.
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These are the item-by-item cuing method, the blocked-cuing method, and the ‘‘only’’ cuing method. The methods differ in the placement of the remember and forget cues and in the cognitive processes proposed to produce differential recall of the TBR and TBF items. Item-by-Item Cuing In item-by-item cued directed-forgetting tasks, items (usually concrete nouns) are presented to participants either verbally or visually, in a list form. The cue to remember or forget an item is presented either immediately prior to item presentation (Muther, 1965), simultaneously with each item presentation (Weiner & Reed, 1969), or immediately following the presentation of each item (Geiselman & Bagheri, 1985; Lehman & Bovasso, 1993). For example, if the item cue follows item presentation, within 5s following the presentation of each item, a cue to remember or forget is also presented (i.e., ROCK . . . forget . . . CAR . . . remember . . . HOUSE . . . forget . . . SQUARE . . . remember . . .). The most common method of cuing items as TBF or TBR in an itemby-item cued task is through the presentation of the words ‘‘remember’’ or ‘‘forget,’’ either visually or auditorially. A symbol or color that represents the cue word has also been used with visual cuing. For example, a red dot following the presentation of an item could signal the participant to forget the item, whereas a green dot following the presentation of an item could signal the participant to remember the item. When the item-by-item method is used, directed-forgetting effects (e.g., higher recall of TBR than TBF items) are produced by selective rehearsal of the to-be-remembered items and nonrehearsal of the to-be-forgotten items (Geiselman, Rabow, Wachtel, & MacKinnon, 1985; MacLeod, 1975; Woodward, Bjork, & Jongeward, 1973). Evidence for a selective rehearsal mechanism is supported by lower recall and recognition of TBF items than of TBR items (Davis & Okada, 1971; Zacks & Hasher, 1994). Recall of TBF items is lower than recall of TBR items, as would be expected in a directed-forgetting study. It is the unequal recognition of the TBR and TBF items that indicates that directed-forgetting in recall is a product of selective rehearsal. If both item types were encoded and the TBF items were inhibited at recall, then both item types should be available in recognition memory. However, poorer recognition memory for the TBF items indicates that the TBF items are not encoded during item learning. The timing of cues does not produce differences in item-by-item directedforgetting. Presenting the remember or forget cue immediately before item presentation, simultaneously with item presentation, or immediately following item presentation allows subjects to selectively rehearse the TBR items equally as well during list presentation. This conclusion is drawn based on anecdotal evidence presented by both Woodward and Bjork (1971) and Geiselman and Bagheri (1985). Both sets of authors reported that participants
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in experiments using the item-by-item cuing method described their memory strategy as determining if each item was to be cued as TBF or TBR and then rehearsing only the TBR items. Until the presentation of the cue, participants rehearsed neither the TBF nor the TBR items. Only after the cue was given did the participants begin to rehearse the TBR items. Empirical evidence is needed to back up these anecdotal claims. The item-by-item cuing method could be used as a measure of resistance to interference, although an experiment such as this has not been reported. Interference could be manipulated in two ways in an item-by-item cued task. Interference could be created by the dual task nature of an item-by-item cued task. That is, participants are required to perform two tasks simultaneously, to remember certain words and forget others. Interference from one task requirement could interfere with the other task requirement, making one task more difficult to perform than the other. Interference could also be created by the relationships between items. For example, if the items were semantically related it would be difficult to forget certain items and remember others, because the semantic relationship promotes the retrieval of related items. Blocked-Cuing A second method used to produce directed-forgetting effects is the blocked cuing method (Bjork, 1970; Bruce & Papay, 1970). In this task, participants are presented with a list of words that is divided into two sets. Between the presentation of each set, participants are given a signal that indicates they should forget the words in the first set. The ‘‘signal’’ can range from being told to ‘‘forget the first list half or item set’’ (Geiselman, Bjork, & Fishman, 1983) to the sounding of a buzzer (Bruce & Papay, 1970; Elmes et al., 1970). The items presented prior to the signal become TBF items and those following the signal become TBR items (i.e., ROCK . . . CAR . . . forget first listhalf . . . HOUSE . . . SQUARE . . . ). In a blocked-cued task, participants are usually not informed that there will be a forget cue. If they are informed that a forget cue will be presented, they are not told when the forget cue will be given during item presentation. This ensures that participants study all of the items presented, not just the TBR items. Just as in item-by-item cuing, when both item types are requested at recall, lower recall of TBF items than of TBR items is found (i.e., directedforgetting effects). However, unlike item-by-item cuing, equal recognition of both item types is found (Elmes et al., 1970), indicating some degree of encoding of all of the items. If both the TBF and the TBR items are encoded, the differential effects of a forget or remember cue at recall cannot be due to selective rehearsal. Differential recall of TBF and TBR items is due to retrieval inhibition (Bjork, 1989). The TBF items are inhibited and not recalled, while the TBR items are not inhibited and recalled. The midlist presentation of the forget cue allows the TBR items to be rehearsed selectively. Therefore, selective rehearsal probably plays a role in
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promoting retrieval of the TBR items. However, the inferior retrieval of the TBF items is due to retrieval inhibition. ‘‘Only’’ Cuing The third and least frequently used directed-forgetting cuing method is the ‘‘only’’ cuing method (Epstein, 1969). In the ‘‘only’’ cuing method, items are presented in two temporally ordered blocks and the forget cue is given following the presentation of both blocks of items. The two most common methods of segregating block one from block two are creating a background color change following the presentation of the first block (Bjork, 1970; Block, 1971) or creating blocks with two different item types, such as presenting numbers in the first block and words in the second block (Epstein, 1969). No information is given at item presentation concerning the block of items that will be assessed at recall. After the presentation of both blocks, participants are instructed to recall ‘‘only’’ the first block or ‘‘only’’ the second block (i.e., blue background . . . ROCK . . . CAR . . . yellow background . . . HOUSE . . . DOG . . . recall words on the blue background) (see Jongeward, Woodward, & Bjork, 1975, and Roediger & Tulving, 1979, for alternate versions of the ‘‘only’’ cue). The TBR items are the block of items requested at recall, and the TBF items are the block of items which are not requested at recall. Recall of items in an ‘‘only’’ condition in which an ‘‘only’’ instruction is presented at recall is compared to recall of the same list in a control condition in which no ‘‘only’’ cue is given at recall. Directed-forgetting effects are inferred from the number of TBR items recalled. The number of TBR items recalled in the ‘‘only’’ condition is compared to the number of items recalled in the corresponding set in the control condition (Bjork, 1972). Efficient directed-forgetting effects are found if significantly more TBR items are recalled in the ‘‘only’’ condition than in the corresponding set in the control condition. It has been proposed that the forget cue in the ‘‘only’’ condition blocks access routes to the TBF item set. This decreases the interference from the TBF item set in TBR item set recall. That is, fewer irrelevant items are available to decrease TBR recall in the ‘‘only’’ condition as compared to the control condition (Epstein, Massaro, & Wilder, 1972). Set differentiation and selective search during retrieval have been proposed to be responsible for directed-forgetting effects in ‘‘only’’ cued tasks (Epstein, 1969; Epstein et al., 1972; Block, 1971). It has been proposed that participants are able to input items into separate sets in memory. At recall, participants search ‘‘only’’ the requested item set. Because participants do not know which item set is TBR and which is TBF until the recall instructions are given, the selective search mechanism must be occurring at retrieval. Alternately, retrieval inhibition may be the mechanism responsible for directed-forgetting effects in ‘‘only’’ cued tasks. Participants are able to inhibit
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the TBF items at recall. The TBF items do not decrease TBR recall. If inhibition is the mechanism producing directed-forgetting effects in an ‘‘only’’ cued task, both the TBF and the TBR items should be available in memory on a recognition test. Block (1971) tested recognition of block one items by subjects who were presented two blocks of items and asked to recall items ‘‘only’’ from the second block (TBR set of items). He found equivalent recognition of block one items (TBF set of items) in the ‘‘only’’ condition and in participants who studied both lists but who were not given an ‘‘only’’ cue. This supports an inhibition interpretation of these results. Although the first list-half items were not recalled, they were encoded to some degree and recognized as well as the items that were recalled. Block interpreted these results as indicating that a retrieval mechanism was operating to produce this pattern of results. However, he interpreted this mechanism as a set differentiation mechanism occurring at item retrieval instead of as an inhibition explanation. Both the retrieval inhibition and the set differentiation and selective search explanations can be thought of as emphasizing different aspects of the same process. In order for only the TBR items to be recalled, the TBR and TBF items must be differentiated into sets, the TBF items must be inhibited, and the TBR items must be selectively searched at recall. Unlike blocked-cued directed-forgetting, selective rehearsal is not manipulated in this task because the ‘‘only’’ cue is presented after the presentation of all of the items. Conclusions Based on these interpretations of the cognitive processes responsible for directed-forgetting in each cuing method, the label ‘‘directed-forgetting’’ is inappropriate for all three methods because none of the methods manipulates ‘‘forgetting.’’ It would be more appropriate to call item-by-item cued directed-forgetting ‘‘directed-nonencoding.’’ Blocked-cued directed-forgetting should be entitled ‘‘directed-inhibition with selective rehearsal.’’ ‘‘Only’’ cued directed-forgetting could then be called ‘‘directed-inhibition.’’ Although not as catchy as the title ‘‘directed-forgetting,’’ these descriptors would promote more accurate interpretations of this body of research. EXAMPLES OF METHODOLOGICAL CONFUSIONS Two of the examples of methodological confusions in the interpretation of directed-forgetting effects can be found in investigations of a release from inhibition and investigations of directed-forgetting in indirect memory. Release from Inhibition One study investigating the release from inhibition process using the directed-forgetting task highlights the problems encountered when the cuing method of the task is not taken into consideration. If an item is inhibited, it should be able to be ‘‘released from inhibition,’’ and the memory should
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then function once again as an uninhibited memory. There have been several investigations into the release from inhibition mechanism to determine if a previously inhibited TBR item can be retrieved (Basden, Basden, & Gargano, 1993; Bjork, 1989; Epstein & Wilder, 1972; Geiselman & Bagheri, 1985; Geiselman et al., 1985; Reed, 1970). Concrete nouns were cued item-by-item as TBR and TBF in an initial study-test trial (Geiselman & Bagheri, 1985). (As discussed above, directedforgetting effects in a study in which items were cued as TBR or TBF itemby-item are produced by selective rehearsal and not retrieval inhibition.) Following item recall in the first study-test trial, all of the items (i.e., both the TBR and TBF items in the first study-test trial) were re-presented as items TBR. The items cued TBF in the first trial and not recalled were more likely to be recalled in the second study-test trial than were items labeled TBR and not recalled in the first study-test trial. These results were interpreted within an inhibition explanation. It was proposed that the TBF items not recalled on the first study-test trial were inhibited and the TBR items not recalled on the first study-test trial were not encoded. The previously unrecalled TBF items, because they were thought to be inhibited on the first study-test trial, received two sources of activation on the second study-test trial: the re-presentation on the second study-test trial and a release from inhibition. The previously unrecalled TBR items, because they were thought to have not been encoded, should receive activation from only the re-presentation. Therefore, the greater recall of the previously unrecalled TBF items as compared to the previously unrecalled TBR items was interpreted as a product of the additional activation given to the previously unrecalled TBF items as they were released from inhibition. However, inhibition was not manipulated in this task, because item-byitem cuing was used and therefore this is an inaccurate interpretation of the results. Instead of investigating a ‘‘release from inhibition,’’ this article was actually investigating the effects of a second presentation of items either not rehearsed or items rehearsed and not recalled during the initial presentation. Directed-Forgetting and Indirect Memory The work on directed-forgetting effects in indirect memory is another example of the problems encountered with inappropriate interpretations of the processes producing directed-forgetting. Three studies have been reported examining directed-forgetting effects in indirect memory as compared to direct memory. The first study of this type, reported by MacLeod (1989), cited evidence that direct and indirect memory are affected similarly by retrieval manipulations. He further proposed that inhibition acts at retrieval to suppress recall of items. Therefore, if inhibition is a retrieval process, then similar patterns of item recall should be found in direct and indirect tests of memory. MacLeod cued items as TBR and TBF item-by-item and reported greater TBR and TBF recall using both direct (e.g., recall and recognition)
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and indirect tests of memory (e.g., fragment completion and lexical decision). Because the items were cued item-by-item, no inhibition was manipulated in this task, although the results were interpreted within an inhibition framework. Two other studies investigating the effect of directed-forgetting manipulations on direct and indirect memory have produced results that contradict those of MacLeod. Both Paller (1990) and Basden et al. (1993) found directed-forgetting effects using direct memory tests when remember and forget items were cued item-by-item. Counter to MacLeod, they also found equal priming of TBR and TBF items using indirect memory tests when items were cued item-by-item. In addition, Basden et al. (1993) also reported directed-forgetting effects in direct memory and equal TBR and TBF item priming in indirect memory tests using a blocked-cued directed-forgetting task. Both TBR and TBF items, whether cued with blocked or item-by-item cuing, should show equal priming when tested using indirect memory tests. This should occur because the only criteria necessary to produce priming on a indirect memory test is exposure to an item (Schacter, 1987). Both the TBR and TBF items are presented to the participant in item-by-item and blocked-cued tasks. In MacLeod’s (1989) study participants were presented lists of 100 words. They were repeatedly told before list learning that the list to be presented was long and difficult to remember. They were also informed that their best strategy was not to study the TBF items because they would not be tested on them. In addition, each item was presented only for one second, and item cuing was presented after the item. Not only did each participant have little time to study each word, but he or she also did not have to process an item until he or she could be certain that the item was TBR. Therefore, we believe that the results presented by MacLeod were a product of the list length and item-by-item cuing method and not of inhibition. That is, we believe that participants did not attend to an item unless it was cued as TBR. This would make the TBF items unavailable to both direct and indirect tests of memory. Ironically, the purpose of MacLeod’s paper was to promote the role of inhibition in directed-forgetting, the same purpose as this paper. However, it is important that results of directed-forgetting tasks be interpreted as a product of inhibition only when this interpretation is an accurate one based on the cuing method used in the study. Conclusions Although all three directed-forgetting cuing methods produce greater TBR than TBF recall, this recall pattern is not a product of the same mechanism in all three methods. The item-by-item cuing method manipulates the encoding of the TBR and TBF items. Selective rehearsal of the TBR items and nonrehearsal of the TBF items are thought to produce directed-forgetting in
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this type of task. In support of this assumption, greater recall and recognition of the TBR items is found in comparison with the TBF items. This recall and recognition pattern indicates that the TBR items are not encoded in memory and therefore not recalled following list learning. Both the blocked and ‘‘only’’ cuing methods produce some degree of encoding of the TBR and TBF items as revealed by equal recognition of both item types. However, using blocked cuing, greater recall of the TBR than the TBF items is found. Using ‘‘only’’ cuing, greater TBR recall is found in the ‘‘only’’ condition as compared to the control condition. Therefore, the TBF items must be inhibited at recall in blocked and ‘‘only’’ cued directed-forgetting tasks. Directed-forgetting is an inappropriate label for these methods because none of the three cuing methods manipulates forgetting. Blocked and ‘‘only’’ cuing can be considered methods for examining ‘‘directed-inhibition with or without selective rehearsal.’’ Item-by-item cuing is a method for examining ‘‘directed-selective encoding.’’ The research on release from inhibition and directed-forgetting tests of indirect memory are examples of the problems encountered when the cuing method of a directed-forgetting task is not taken into consideration. DEVELOPMENTAL DIRECTED-FORGETTING STUDIES In this section, the developmental directed-forgetting research is reinterpreted within the cognitive inhibition framework outlined in the previous section. Specifically, it is proposed that item-by-item directed-forgetting effects are produced by selective rehearsal of the TBR and nonrehearsal of the TBF items and that developmental differences in item-by-item cued directedforgetting tasks reflect developmental differences in the efficiency of selective rehearsal. It is also proposed that blocked and ‘‘only’’ cued directedforgetting effects are produced by the inhibition of the TBF items and that developmental differences in directed-forgetting tasks using these cuing methods reflect developmental differences in the efficiency of inhibitory processing. Item-by-Item Cued Developmental Directed-Forgetting Studies Two directed-forgetting studies have been reported using the item-by-item cuing method with children (Foster & Gavelek, 1983; Lehman & Bovasso, 1993). Neither study assessed recognition of items following recall. Both studies report pause time during self-paced item input as a measure of selective rehearsal during item learning. An item-by-item cued developmental directed-forgetting study was reported by Lehman and Bovasso (1993). This study used a ‘‘helping game,’’ in which a honey bee is attempting to find honey. Each child participating in this task is asked to help the bee by remembering where the bee finds honey. The bee finds honey in some ‘‘places’’ but not in others. The places are drawings of everyday objects such as a lamp, a train, and a drum. The
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TBF places were followed by a red X and the TBR places were followed by a honey pot. Study time was self-paced. That is, each child could pause on and study each item for as long as he or she wished during item presentation. It was assumed that the children were rehearsing items during the pause. Pause time or study time during item learning was interpreted as an indication of the amount of rehearsal of each item. The longer the pause, the greater the amount of rehearsal of that item. Seven-, 9- and 11-year-olds and college students participated in two studytest trials in this experiment. In the first study trial, 24 items were presented and cued as TBR and TBF, item-by-item. Approximately half of the items were cued TBF and half were cued TBR. After list presentation, recall of both TBR and TBF items was tested. Lehman and Bovasso tested a release from inhibition using the same procedure outlined in the previous section (cf. Geiselman & Bagheri, 1985) immediately following the first study-test trial. A second study-test trial was presented, which consisted of the presentation of 18 of the ‘‘old’’ items and 6 ‘‘new’’ items. Old items were items that were presented on the first studytest trial, whereas the new items were items that were not presented on the first study-test trial. All of the items in the second study trial were cued as TBR. The old items (i.e., items presented on trial one) that had previously been cued as TBF items were presented as TBR items in the second studytest trial. The old items that had previously been cued as TBR were again cued as TBR in the second study-test trial. Following the second study-test trial, the proportional recall of the TBF and TBR words unrecalled on trial one and recalled on trial two was calculated. Recognition of both item types was also assessed following the second study-test trial. According to previous research (Geiselman & Bagheri, 1985), if inhibition plays a role in this task, there should be a greater proportional recall of the previously unrecalled TBF items than unrecalled TBR items in the second study-test trial. Remember that the reasoning behind this proposition is as follows: if the TBF items on trial one were inhibited and not recalled, then on the second trial when these items were re-presented as TBR they should benefit from a ‘‘release from inhibition’’ as well as a second presentation. The items which were TBR in the first study-test trial and not recalled should benefit from a second presentation but not the release from inhibition because the items were not inhibited in the first study-test trial. The extra activation given to the previously unrecalled TBF items in the form of a release from inhibition should increase recall above that of the previously unrecalled TBR items in the second study-test trial. Therefore, greater recall of the previously unrecalled TBF items than the previously unrecalled TBR items in the second study-test trial would indicate that the TBF items were inhibited in the first study-test trial. The first study-test trial recall and study time results indicated that all ages could produce directed-forgetting effects. That is, more TBR than TBF items
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were recalled at all ages in the first study-test trial. In addition, recall of the TBR items increased with age, and rehearsal time was greater for the TBR items than for the TBF items, with the duration of rehearsal time for the two item types becoming more distinct with age. These rehearsal patterns suggest selective rehearsal of the TBR items and nonrehearsal of the TBF items. In the second study-test trial, no difference in the proportional recall of previously cued and unrecalled TBF and TBR items was found at any age. That is, the TBF items unrecalled on the first study-test trial did not receive any additional activation from a release from inhibition during the second presentation. Because item-by-item cuing was used in this study, no inhibition was manipulated; therefore, no release from inhibition should be found. The unrecalled TBF items were not studied and not encoded, as revealed by the pause times during rehearsal. Foster and Gavelek (1983) used the item-by-item cuing method to study the ‘‘selective processing’’ of TBF and TBR information in boys. First-, third-, and fifth-grade boys participated in this study. In this experiment, the items presented were pictures from six easily recognized categories with four items in each category. A 24-item list was used with the members of three of the categories being designated the TBR items and the members of the remaining three categories being designated the TBF items. The list was presented visually with a red dot or a green dot following each item, with the instructions to forget items followed by red dots and remember items followed by green dots. Each child was allowed to pace his progression of study of the items on the list by pressing a control button that would terminate the cue slide and present the next item. Following list presentation, each child was asked to recall the TBR items. The number of times a TBF item intruded in recall was recorded. The list was re-presented two additional times in the same format and recall of TBR items and TBF intrusions were assessed in both additional trials. The dependent measures in this experiment were TBR item recall, TBF item intrusions in recall, clustering scores (the degree of category clustering produced in recall), rehearsal time (the duration of the pause time following the presentation of each item), and practice effects (differences in rehearsal, recall, and clustering of TBR and TBF items as trials progressed). There were fewer TBF than TBR items recalled at each age. In addition, the difference in TBR and TBF recall increased with age. This difference in recall was a result of greater TBR recall with age and not lower TBF recall with age. TBF recall was very low and did not differ across the age groups. These results suggest that the TBF items were not encoded at any age, and therefore the TBF items were not recalled. The TBR items were encoded and the normal developmental improvements in memory were found. This pattern is similar to that found when the TBF items are explicitly requested at recall in an item-by-item directed-forgetting task (cf. Lehman & Bovasso, 1993).
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In addition, several analyses were reported that suggested selective rehearsal of the TBR items and nonrehearsal of the TBF items. The duration of time spent rehearsing the TBR items increased as the trials progressed. The duration of time spent rehearsing the TBF items decreased as the trials progressed and with age. The degree of clustering increased with age and as the trials progressed. More time was also spent studying TBR items as the children progressed through the list at all ages. Conclusions The results of the Lehman and Bovasso (1993) and Foster and Gavelek (1983) studies support the argument that selective rehearsal is responsible for directed-forgetting effects in item-by-item cuing tasks. Children as young as 7 years old produced directed-forgetting effects in an item-by-item directed-forgetting task. Both studies reported longer pause times at all ages after the presentation of the TBR items in comparison to the TBF items. The authors interpreted these results as an indication of selective rehearsal of the TBR items and nonrehearsal of the TBF items during item study. Because recognition of the TBR and TBF items was not assessed in either study, the selective rehearsal interpretation of directed-forgetting effects in an item-by-item cued task cannot be confirmed. Greater recognition of the TBR than TBF items has been reported in the adult item-by-item cued directed-forgetting literature (Davis & Okada, 1971). These results need to be replicated in the children’s directed-forgetting literature to confirm this hypothesis with children. Blocked Cuing Developmental Directed-Forgetting Studies The developmental directed-forgetting studies that use block cuing consist of several studies reported by Bray and his colleagues (Bray & Ferguson, 1976; Bray, Hersh, & Turner, 1985; Bray, Justice & Simon, 1978; Bray, Justice & Zahm, 1983) and a study by Harnishfeger and Pope (1996). Each of Bray et al.’s studies uses the same methodology, testing participants in ages ranging from first grade to adulthood. The combined results of Bray et al.’s studies present a picture of the development of directed forgetting across childhood, adolescence, and into adulthood. The methodology used by Bray et al. will be described first and then the results of each of these studies will be presented.2 Bray and colleagues used a window projection device that contained eight or ten windows. In each window, black and white drawings of common objects were presented to participants. Each window in the projection unit could 2
Several of the articles reviewed here reported data collected from mentally retarded children and adults. The focus of this review is the development of efficient directed-forgetting performance in normal or average children, so only the results of normal children will be discussed.
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TABLE 1 Conditions in Bray et al. Condition Forget Probe 1 Probe 2 Control Precued
Item cuing 1–4 Blue 1–4 Blue 1–4 Blue 1–4 Blue
background background background
Recall 5–8 Yellow background 5–8 Blue background 5–8 Blue background
5–8 1–4 5–8 1–4
background 5–8 Blue background
5–8
be lit individually, either with the picture presented in it or without displaying a picture. The presentation trials were self-paced. Participants pushed a button on the console when they were ready to progress to the next picture. Participants were asked to recall the pictures in serial order. Therefore, in order for an item to be counted as correct it must have been recalled in its correct serial position. Participants were told that if the background color changed, they should forget the items that had been presented on the first color background (i.e., TBF items) and remember the items presented following the color change (i.e., TBR items). Participants were also told that not all of the trials would contain a background color change, so they must study every item. Five conditions were presented to participants. In the Forget condition, following the presentation of half of the items, the background color changed, with the remaining pictures being presented on a new color background. The forget condition was compared to four other conditions: the Probe 1, Probe 2, Precued, and Control conditions. In the Probe 1 condition, all items were presented on the same color background. Following item presentation, recall of the first half of the items was requested. In the Probe 2 condition, all items were presented on the same color background and retention of the second half of the items was assessed at recall. In the Control condition, half of the list was presented on the same color background in the first half of the windows on the projection unit and recall of these items was assessed. In the Precued condition, half of the items were presented in the second half of the windows of the projection unit on the same color background and recall of these items was assessed. Table 1 presents a summary of Bray et al.’s conditions. The first two columns indicate the items presented and the color backgrounds on which the items were presented. The third column indicates the items requested at recall. Directed-forgetting effects were proposed to be found if two results oc-
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curred: First, recall accuracy should be higher on Forget trials than on Probe 2 trials, indicating that a facilitation in the recall of the second list-half occurred from the forget cue. That is, recall of the second list-half should be greater following the forget cue because this cue parcels off the first listhalf items so that they do not hinder second list-half recall. In the Probe 2 condition, the first list-half items are not parceled off by the forget cue. Recall of the second list-half with no forget cue should be subject to interference from the first list-half items, resulting in lower second-list-half recall. Second, recall accuracy on Forget, Precued, and Control trials should not differ, confirming that the interference from the first-list-half items was eliminated by the forget cue. That is, if the forget cue is effective, recall of the second list-half, although preceded by the presentation of the first list-half of items, should be equal to the Precued and Control conditions in which only one list-half is presented and tested. Bray et al. (1983) tested first, third and fifth graders with this procedure. Adults were investigated in a separate experiment. Children were presented eight items in the window projection device. The duration each person paused following the presentation of each item as he or she progressed through the list was assessed to investigate item rehearsal. There was no difference in recall of the second list-half items in the Forget condition and the Probe 2 condition for the first graders. Second list-half recall in the Forget condition was also lower than the recall in the Precued and Control conditions. Thus, the forget cue did not eliminate interference from the TBF items, nor did it facilitate recall of the TBR list-half for the first graders. By third grade, there was a significant difference in the secondlist-half recall across conditions, with higher recall in the Forget condition than the Probe 2 condition. Recall was equal in the Forget and Control conditions. However, the second-list-half recall was still greater in the Precued condition than in the Forget condition, which did not conform to patterns reflecting efficient directed-forgetting performance. Thus, there was some facilitation of recall due to the forget cue in third grade, but the interference from the TBF list-half was not eliminated by this cue. A facilitation in recall was seen in the fifth graders, with the recall of the TBR items being higher in the Forget condition than in the Probe 2 condition. The fifth graders also produced equal TBR item recall in the Forget, Precued, and Control conditions. Bray et al. concluded that, by fifth grade, the forget cue both decreased the interference from the TBF list and facilitated the recall of the TBR items. In a second experiment, adults participated in the previously described procedures, with the only change being that adults studied ten pictures instead of eight. Adults were able to use the forget cue to reduce the interference from the TBF items. Second-list-half recall in the Forget condition was higher than that in the Probe 2 condition, and the recall of the Forget, Control, and Precued conditions did not differ. Adults are efficient inhibitors in a
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blocked-cued task. An important difference in the fifth-grade children’s and adults’ data, however, was in the pause time analysis. Pause time on each item during item learning was used as a measure of rehearsal. Bray et al. (1983) predicted that selective rehearsal was the strategy used to decrease interference from TBF items in TBR recall. If this prediction is accurate, then pause times should increase as the number of items presented increases. Pause times should then be reset following the forget cue because the previously presented items (the TBF items) are no longer being rehearsed. Pause time should increase again as the remaining items (the TBR items) are presented. The adult pause time data produced the predicted rehearsal patterns. In the Forget condition, adult pause time steadily increased from items one to five. Following the forget cue, the pause times dropped back to close to initial rehearsal level and began to increase again as the participant progressed through items six through ten. The pause times of the Probe trials increased until the participants reached item six and then pause time decreased. The pause times of the Control and Precued conditions were not significantly different from those of the first five serial positions of the other three conditions. Bray et al. interpreted the pause time patterns in adults’ performance as mature selective rehearsal. The first-, third-, and fifth-grade children produced equal pauses across item types. That is, children paused as each item was presented, which indicated that the items were being rehearsed, but their pause times did not increase with the presentation of items. They also did not ‘‘reset’’ their pause times following the forget cue in the Forget condition. These results were interpreted as reflecting immature selective rehearsal of the items. Although third and fifth graders could use the forget cue to eliminate selective interference from the TBF items, they were not using a rehearsal strategy similar to the adult’s rehearsal strategy to produce these effects. Bray et al. interpreted the pause time patterns of the children and adults as indicating two transitions in the effective use of a forget cue to eliminate interference from TBR items. By fifth grade, children are able to efficiently use the forget cue to disregard the TBF items, but they are not using selective rehearsal to perform this task. The ability to selectively rehearse the TBR items becomes available after fifth grade. Based on the results of Bray et al. (1983), it can be concluded that children become efficient inhibitors before they become efficient selective rehearsers. These results discredit the selective rehearsal interpretation of directed-forgetting effects in a blocked-cued task by showing that mature selective rehearsal need not be developed in order for efficient inhibition of the TBF items to be found. This study was extended by Bray et al. (1985), who used the same procedures with fifth, ninth, and twelfth graders. In this study, a ten-window projection device was used to present the items and pause time was again as-
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sessed. The recall accuracy data replicated that of Bray et al. (1983), with all ages producing higher recall accuracy in the Forget condition than in the Probe 2 condition. No differences in recall in the Forget, Precued, and Control conditions were found at any age. These results indicated that the TBF items did not hinder the recall of the TBR items at any ages. All ages in this study could produce directed-forgetting effects. As an additional analysis, students were divided into groups depending on whether or not they spontaneously rehearsed as they learned the items. Out of a total of 16 possible participants in each group, there were four fifth-grade rehearsers, ten ninth-grade rehearsers and eleven twelfth-grade rehearsers. Both the rehearsers and nonrehearsers produced directed-forgetting effects. These findings confirm those of Bray et al. (1983), suggesting that the ability to use a forget cue to decrease the interference of TBF information in TBR item recall is mature by fifth grade, and this ability is not due to mature selective rehearsal of the TBR items. Bray and Ferguson (1976) investigated directed-forgetting in 7-year-old children using an eight-window testing console. Study was not subject paced, so selective rehearsal data was not available from this study. Every item was presented for 3 s. Recall accuracy was significantly higher in Forget than in the Probe 2 condition, indicating that a facilitation in recall was provided by the forget cue. However, the Precued condition recall was equal to that of the Forget condition, and the Control condition recall was lower than that of both the Precued and Forget conditions. Recall accuracy was facilitated in the Forget condition above that of the Probe 2 condition, but some interference was still produced by the TBF items in the Forget condition. Contrary to Bray et al. (1983), it can be concluded that some inhibitory ability can be found in 7-year olds, but in accord with Bray et al. (1983), inhibitory ability does not mature until later in childhood. Bray et al. (1978) tested 14-year-olds with a ten-window projection console. In this study, they used only the Forget condition to study the amount of interference produced by the TBF items in the recall of the TBR items as the number of TBF items increased. The number of items presented before and after the color change was varied in the forget trials. Either 0, 2, 4, or 6 TBF items were presented before a color change. After the color change, either 2, 4, or 6 TBR items were presented. This produced the following combination of trials: F0:R2, F0:R4, F0:R6, F2:R2, F4:R2, F6:R2, F4:R4, F6:R4. For example, in the F2:R2 trial, two items were presented, the color background changed indicating that the previously presented words were TBF, and then two items were presented which were TBR. Some trials did not include a color change (e.g., F0:R2, F0:R4, and F0:R6) which increased the likelihood that participants encoded all of the items. There was no interference in the recall of the TBR items in trials which included TBF items. As the number of TBF items increased, there continued to be no interference of the TBF items. In other words, there was no differ-
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ence in the number of TBR items recalled as a function of the number of TBF items presented prior to the TBR items. By age 14, adolescents can use a forget cue to eliminate the interference of up to six TBF items in the recall of the TBR items. If efficient inhibition is the mechanism producing directed-forgetting effects in these studies, there should be equal recognition of the TBF and TBR items. Bray et al.’s studies, however, focus on the fate of the TBR items and the availability of the TBF items was not assessed. The work reported by Bray and his colleagues calls into question selective rehearsal as the mechanism responsible for efficient forgetting in a blocked-cued task by demonstrating that efficient directed-forgetting is produced before selective rehearsal becomes mature. However, definitive conclusions concerning the role of retrieval inhibition in directed-forgetting cannot be made from this series of studies because the availability of the TBF items in memory was not assessed. We (Harnishfeger & Pope, 1996) conducted a developmental directedforgetting study using blocked cuing in which the recall and recognition of both the TBF and TBR items was assessed in order to determine the role of retrieval inhibition in the development of directed-forgetting. We predicted that as inhibitory ability becomes mature, fewer TBF items would be produced at recall, but both the TBF and TBR items would be equally recognizable. In our study, 20 unrelated items were presented verbally in two 10item sets to first, third, fifth graders, and adults. There were three conditions: the Remember–All, Forget–All, and Forget–Only conditions. (The first word in the condition name refers to the instruction given following the presentation of the first item set. The second word in the condition name refers to the instruction given at recall.) In the Remember-All condition, children and adults were presented the first item set and then they were told to continue trying to remember the words and also to remember the remaining words to be presented (set two). At recall, they were asked to recall all of the words that they had heard. Children and adults in the Forget–All condition were told, following the presentation of the first item set, to forget the first ten words that they had heard and to remember only the second item set. At recall, they were asked to recall all of the words, including the words they had been told to forget. Participants in the Forget–Only condition were told to forget the first ten words or the first item set and to remember only the second item set. At recall, they were asked to recall, only the words that they had been told to remember (set two). Following the recall test, participants in each condition completed a recognition test of all the words included in the list plus 20 unrelated foils. We argued that efficient directed-forgetting would be produced if: (1) The within-participant comparison in the Forget–All condition revealed greater recall of the second item set than of the first item set, indicating that the
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TBF items were inhibited in comparison to the TBR items. (2) The betweenparticipant comparison yielded greater recall of the first item set in the Remember–All condition than in the first item set of the Forget–All condition. This would indicate that the items in the first item set (TBF items) in the Forget–All condition are inhibited in comparison to the items in the first item set (TBR items) of the Remember–All group.3 A comparison between the number of TBF items produced in the Forget–All and Forget–Only conditions was used as an additional measure of inhibitory ability. Efficient inhibitors should be able to withhold an inhibited but remembered response in the Forget–Only condition. Thus, more TBF items should be recalled in the Forget–All condition in comparison to the Forget–Only condition in individuals who are efficient inhibitors. The adults and the fifth graders produced both the within- and betweenparticipant inhibition effects, indicating that inhibitory ability is functioning by fifth grade. Only the first comparison (i.e., significantly higher recall in the first list-half than in the second list-half of the Forget–All condition) was significant for the third graders. Neither effect was found for the first graders. There was no difference in the number of TBF items produced in the Forget– Only and the Forget–All conditions in each of the children’s groups. Adults, however, recalled fewer TBF items in the Forget–Only than in the Forget– All condition. Although fifth graders can produce adultlike between- and within-participant inhibition effects, their inhibitory ability is not as mature as adults because they did not withhold inhibited but remembered items when asked to do so. Some inhibitory ability is present by third grade, a bit more inhibitory ability is mature in fifth grade, but inhibitory efficiency continues to develop between fifth grade and adulthood. The critical element of our study for this discussion was the inclusion of a recognition test following the recall test. This was included to determine if the TBF items, although not produced at recall, were encoded to some degree in memory. If this is the case, then selective rehearsal could not be the mechanism responsible for directed forgetting; rather, inhibition must be the process activated by the forget cue because, although the TBF items were not recalled, they were encoded to some degree. The results indicated that recognition was high and there was no difference in recognition by item type or across age level. There were slightly more items recognized in the first item set than in the second item set of the Remember–All condition, indicating a primacy effect. There were, however, 3
A preferable method of analyzing the data in this experiment would have been to examine the differences between TBR and TBF item recall at each age. A smaller difference in TBR and TBF item recall in the Forget conditions at younger ages and a greater difference at older ages would indicate inhibitory efficiency at older ages. This would be statistically more sound because it would eliminate the reliance on accepting the null hypothesis that there is no difference in TBR and TBF recall at young ages.
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no differences in recognition across item sets in the remaining conditions. Therefore, the results of this study support the conclusion that efficient inhibition produces directed-forgetting effects in a blocked-cued task. Conclusions Bray’s studies argue against the selective rehearsal explanation of blocked-cued directed-forgetting by discovering that efficient forgetting can be produced without mature selective rehearsal. These results point to an alternate mechanism, namely retrieval inhibition, which is responsible for directed-forgetting using blocked-cuing. Bray et al.’s methods, however, do not allow for the investigation of such a mechanism because the availability of the TBF items was not assessed. We (Harnishfeger & Pope, 1996) directly investigated the role of retrieval inhibition in a block cued directed-forgetting study by measuring the recall and the recognition of both the TBF and TBR items. We found that, although the TBF items are not produced at recall, they are available in recognition memory, indicating that the TBF items are encoded to some degree. Evidence from both Harnishfeger et al. and Bray et al. suggests that retrieval inhibition has reached a functional level by fifth grade, with some evidence suggesting that some inhibitory ability may be available as early as first or second grade (Bray & Ferguson, 1976). It can also be concluded that inhibitory ability continues to develop between childhood and adulthood. ‘‘Only’’ Cued Developmental Directed-Forgetting Studies Two studies with children have investigated the ‘‘Only’’ cue in a directedforgetting task (Howard & Goldin, 1979; Posnansky, 1976). Posnansky (1976, Exp. 1) used item-by-item cuing in a directed-forgetting task with third and seventh graders in which an ‘‘only’’ cue was presented at recall. This study was a test to determine if the selective search interpretation of directed-forgetting proposed by Epstein (1972) or the selective rehearsal interpretation of directed-forgetting proposed by Bjork (1972) was responsible for directed-forgetting effects. She presented 16 words on index cards. Each word was followed by either a green dot, indicating that the item was TBR, or a red dot, indicating that the item was TBF. She also varied the categorical construction of the list by presenting three types of lists. In the Category-Consistent list, the TBR and the TBF items were each made up of two semantic categories of items. In the CategoryInconsistent list, the TBF items and TBR items were made up of the same four categories, but the items were not separated into cue type by category. In the Noncategorized items, the lists were made up of unrelated items. Each item was presented twice to participants during input. Following list presentation, participants were asked to recall either only the TBR items (Recall– Only condition) or all of the items including the TBF items (Recall–All condition). A second recall test was given in which all participants (both the
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Recall–All and Recall–Only conditions) were asked to recall all of the items that they could remember. A recognition test which included the 16 items and 16 foils was presented immediately following the second recall and then an additional recognition test was given after a 5-min delay. There was greater TBR than TBF recall in both the Recall–Only and Recall–All conditions at both ages. More TBR items were recalled in the Recall–Only condition at both ages than in the Recall–All condition, indicating that the ‘‘only’’ instruction facilitated TBR recall. More items were recalled from the category consistent list than from the other two list types. At second recall, in which all of the children were asked to recall both the TBR and TBF items, more TBR items were again recalled by the children who were previously in the Recall–Only group than the Recall–All group. Recognition was equal for both the TBF and TBR items both immediately after the second recall and again following a 5-min delay. Posnnasky interpreted these data as being the result of an ‘‘only’’ effect. She suggested that the ‘‘only’’ cue presented at recall in the Recall–Only condition reduced the interference from the TBF items. This limited the search set at recall to only the TBR items and increased the recall of the TBR items. However, this explanation of the results is not logical based on the item-by-item cuing method used to tag items as TBR and TBF. The TBF items should not be available in memory in an item-by-item cuing task because they should not have been rehearsed during item learning. Therefore, the TBF items should not decrease TBR recall in the Recall–All condition. However, the multiple presentations of the items at input probably produced sufficient encoding of the TBF items to make them available in memory. As discussed earlier in this paper, an ‘‘only’’ cue given at recall may produce directed-forgetting effects through retrieval inhibition of the TBF items. All of the items must have been encoded in memory to some degree if this is to occur. Because the multiple presentations probably allowed for the encoding of both the TBR and TBF items, Posnansky’s interpretation of the data was probably correct. The ‘‘only’’ cue at recall reduced the interference from the TBF items so that more TBR items could be recalled. The ‘‘only’’ cue probably produced these results through inhibition of the TBF items. The results of Bray and Ferguson (1976) suggest that some efficient inhibition may be mature early in childhood. Posnansky found efficient inhibition in third grade. In a second study, Posnansky (1976, Exp. 2) used the ‘‘only’’ cue to determine if it could facilitate the recall of the TBR items in both third and seventh graders in a traditional ‘‘only’’ cued condition (as outlined in the second section of this paper). Eight different eight-item lists were presented to thirdgrade children and eight different ten-item lists were presented to the seventh graders in this study. To signify list halves, the first four or five items (Group A) were presented written in red ink and the second four or five items (Group B) were presented written in green ink. The colors were used to signify item
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groups to the children instead of the letters A and B. The three conditions used in the previous study were again used in Experiment 2. These are the Category-Consistent condition, the Category-Inconsistent condition, and the Noncategorized condition. Each child participated in eight different studytest trials in this experiment. Two study-test trials were completed with each of the following recall instructions using different lists in each study-test trial: recall Group A, recall Group B (‘‘Only’’ conditions), recall Group A then Group B, or recall Group B then Group A (Controls). Following the eight study-test trials, recall of all items (both TBR and TBF) was assessed. A recognition test of all items was presented following the second recall test in all of the conditions. The third graders recalled an equal number of TBR items under the ‘‘only’’ instructions and in the Control. That is, there was no facilitation of the third graders’ recall of TBR items in the ‘‘Only’’ Condition over the Control. The seventh graders, however, recalled more TBR items under the ‘‘only’’ instructions (with either list A or B assessed at recall) than under the Control instructions. There was no interaction of the type of categorization of the list and the type of recall cue. Recognition was equal across items types for both age groups. The TBF items were available to some degree in the seventh graders’ memory, although they were not recalled during the first or second recall trials. Posnansky concluded that seventh graders could make use of an ‘‘only’’ cue to reduce the interference from the TBF items in the recall of the TBR items. In addition, she argued that this reduction in interference of the TBF items was not due to selective rehearsal because the TBR items were not indicated until recall and could not be selectively rehearsed. Furthermore, the TBF items are not ‘‘erased’’ from memory because they are available in recognition memory. She labeled this phenomenon ‘‘selective processing at recall.’’ Selective processing at recall could be achieved by retrieval inhibition of the TBF block of items. The TBF item block is inhibited, producing low recall of the TBF items. In addition, the TBF items do not hinder TBR item recall and therefore TBR item recall is high. Because no ages were tested between third and seventh grade, additional investigations need to be completed in order to confirm the specific age at which efficient inhibition develops within this task. Efficient inhibition was found by third grade in Posnansky’s first study, in which item-by-item cuing was used to present items and an ‘‘only’’ cue was given at recall. However, efficient inhibition was not found until seventh grade in a traditional ‘‘only’’ cued task. Because of the multiple presentations of each item in Posnsnaky’s first study, the recall of the items was probably not as resource consuming as recall of the items in her second study. If efficient inhibition is a resource consuming process (cf. Engle, 1996; Engle, Conway, Tuholski, & Shisler, 1995), then the low resource demands
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of this retrieval task may have allowed for efficient inhibition to be produced in the first study. Future research should investigate this issue. Howard and Goldin (1979) reported a study with kindergartners that may be classified as a version of an ‘‘only’’ cued directed-forgetting study. The purpose of this study was to assess kindergartners’ ability to allocate their mental resources to TBR information either during initial encoding of information or following encoding of information. In this study, children were asked to help a secret agent named ‘‘Amy’’ remember what she needs to wear when she meets a messenger who will be giving her secret documents. There were four accessories or dimensions which Amy could use to identify herself to the messenger: her hat, belt, neck accessory, or flower. There were four versions of each dimension (e.g., different style of hat, belt, neck accessory, or flower). Each child was presented with either one, two, or four of dimensions at input and then tested on either one, two, or four of the dimensions at recall. The combinations of input dimensions and output dimensions yielded the following conditions, in which the first number refers to the number of dimensions presented at input and the second number refers to the number of dimensions requested at recall: 1/1, 2/1, 4/1, 2/2, 4/2, 4/4. For example, in the 4/1 condition, the child would be told at input that he/she needed to remember the type of Amy’s hat, belt, neck accessory, and flower. At recall, the child would be asked only to recall one dimension, such as her flower color. Children were also presented with the dimensions that were cued as TBR either before (Cue Before) or after (Cue After) the presentation of the dimensions in each trial. In the Cue Before condition, the children were initially told which dimensions would be tested and then they were presented with the dimensions to be studied. For example, in the 4/2 Cue Before condition, children were told that only two dimensions would be relevant, say the belt and the hat. They were then presented with versions of all four dimensions. Following item presentation, a picture of Amy without accessories was presented and the children were asked to fill in the correct responses for only the items which were TBR (belt and hat). This condition manipulates selective rehearsal, because children know which items will be tested before item input and so they should study only those items. Children in the Cue After condition were presented with either one, two, or four dimensions. The children were not told which dimensions would be tested at recall. Therefore, they had to study all of the presented dimensions. At recall, they were tested on either one, two, or four of the presented dimensions. For example, in the 4/2 Cue After condition, the children were presented with an example of all four clothing items at study. At recall, the child was asked to recall the examples of only two of the clothing items. The ‘‘only’’ condition in this experiment is manipulated in the Cue After conditions in which more items are presented than are tested. Thus, the 4/1, 4/2, and 2/1 conditions can be considered the ‘‘only’’ cue conditions,
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because more items are presented than requested at recall. The 1/1, 2/2, and 4/4 conditions can be considered the controls because all items are presented at input and all items are requested at output, making all of the items TBR. The results of this study were presented in terms of the number of errors produced at recall given the number of items presented at input and requested at recall. The logic behind reliance on the error data is that if the cues are used to successfully eliminate the interference from the nontested (or TBF) items, as the number of TBF items increases, errors should not increase. This should be the outcome because processing is devoted exclusively to the TBR items. There should also be a decrease in errors as the number of TBR items decreases, because there are fewer items to be processed. In the Cue Before condition, the children were able to eliminate all interference from the TBF items. There was no difference in the number of errors produced as the number of dimensions presented increased. This occurred because children were able to study only those dimensions which were TBR. There was also a decrease in errors as the number of dimensions tested (or TBR items) decreased. Howard and Goldin interpreted these results as an indication that kindergarten children could allocate their mental resources only to the TBR information if it was indicated during encoding. That is, the children selectively rehearsed the TBR items and did not rehearse the TBF items. In the Cue After condition, the number of errors increased as both the number of items presented and the number of items tested increased. Also, the most errors were made in the 4/1 and 4/2 conditions (‘‘Only’’ conditions) when four dimensions were presented but only 1 or 2 were required at recall. In contrast, fewer errors were made when four items were presented at input and all four were tested at recall (Control conditions). Thus, the interference from the TBF items was not eliminated at recall by the ‘‘only’’ cue because more errors were produced in the ‘‘Only’’ Conditions than in the Control Conditions. Howard and Goldin interpreted these results as indicating that kindergartners could not selectively allocate their mental resources to the TBR information after both the TBR and TBF information had been encoded. In other words, the kindergartners could not inhibit the TBF items and recall only the TBR items. Conclusions From Posnansky’s work it appears that both the TBR and TBF items in an ‘‘only’’ cue directed-forgetting study are available to some degree in memory through recognition tests, but the TBR items are not recalled following item learning. The ‘‘only’’ cue probably manipulates retrieval inhibition in an ‘‘only’’ cued task. Traditional ‘‘only’’ cued directed-forgetting tasks produce directed-forgetting effects by seventh grade. However, the results of Posnansky’s first study suggest that efficient directed-forgetting with an ‘‘only’’ cued task may be found as young as third grade. Howard and Gol-
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TABLE 2 Directed-Forgetting Cuing Methods and the Cognitive Processes Which Produce DirectedForgetting Effects Cuing method
Recall patterns
Recognition patterns
Cognitive process
Item-by-item
TBR . TBF
TBR . TBF
Blocked
TBR . TBF
TBR 5 TBF
‘‘Only’’
TBR . TBF
TBR 5 TBF
Selective rehearsal of TBR items and nonrehearsal of TBF items. Retrieval inhibition of TBF items and selective rehearsal of TBR items. Retrieval inhibition of TBF items. TBR items are not selectively rehearsed.
din’s work confirms this conclusion. They reported that kindergarten age children cannot reduce the interference from TBF items in TBR item recall. In other words, kindergarten age children cannot inhibit the TBF items. CONCLUSIONS The purposes of this review were: (1) to end the confusion over the cognitive processes responsible for directed-forgetting in the three types of directed-forgetting tasks, (2) to highlight the role of cognitive inhibition in the blocked and ‘‘only’’ cued directed-forgetting tasks, and (3) to review and reinterpret the developmental directed-forgetting literature within this framework. Table 2 presents a summary of the directed-forgetting cuing methods and the cognitive processes which produce directed-forgetting using each cuing method. We propose that selective rehearsal produces directed-forgetting effects in item-by-item cued procedures. Evidence supporting this proposal comes from the adult literature in which comparable recall and recognition of TBR and TBF items have been found (Davis & Okada, 1971). In item-by-item cued tasks, the TBF items are not rehearsed during list presentation and therefore they are not available in memory, whereas the TBR items are rehearsed and available in memory. This selective rehearsal pattern produces greater recall as well as recognition of the TBR than the TBF items. Additional evidence for the selective rehearsal mechanism was found in the greater pause times following the presentation of the TBR items than of the TBF items. This evidence indicates that the TBR items are more likely to be rehearsed at input than are the TBF items. Retrieval inhibition is the mechanism responsible for directed-forgetting effects in blocked cuing procedures. This conclusion is based on the differential recall and recognition patterns of the TBR and TBF items. The TBR
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items are more likely to be recalled than the TBF items, but both item types are equally likely to be recognized (Geiselman et al., 1983; Harnishfeger & Pope, 1996). Because the TBF items are recognized equally as well as the TBR items, the TBF items are available in memory to some degree but are not produced at recall. That is, the TBF items are inhibited at recall. Additional evidence for an inhibition interpretation of blocked-cued directed-forgetting effects comes from Bray et al.’s work which suggests that this effect is not due to mature selective rehearsal. Retrieval inhibition is also the mechanism responsible for directed-forgetting effects in ‘‘only’’ cued procedures. Greater recall in an ‘‘only’’ condition, as compared to a control condition with equal recognition of both item types, has been found using the ‘‘only’’ cue (Block, 1971; Posnansky, 1976, Exp. 2). Children can produce directed-forgetting effects using selective rehearsal in an item-by-item cuing procedure by first or second grade (Foster & Gavelek, 1983; Lehman & Bovasso, 1993). The developmental work in this area suggests that inhibition is sufficiently developed by fifth grade, allowing directed-forgetting effects to be produced by this age in blocked cuing tasks (Bray et al., 1983; Harnishfeger & Pope, 1996). The developmental work with ‘‘only’’ cued directed-forgetting tasks suggests that the ability to inhibit TBF items in an ‘‘only’’ cued procedure develops between third and seventh grade. DIRECTIONS FOR FUTURE RESEARCH We suggest that future research should focus on three topics: (1) correcting the problems associated with directed-forgetting methodologies, (2) the inhibition mechanism, and (3) applications for directed-forgetting research. The directed-forgetting task itself is problematic. For example, in a blocked cuing task, the TBF items are always the first block of items presented to participants. Therefore, the cuing of items is confounded with position of the items. The ‘‘only’’ cued directed-forgetting task handles some of these problems by cuing items following item presentation. Cuing is an issue in item-byitem cued tasks as well. Items in these tasks are usually cued randomly with no more than two or three items being cued similarly in a sequence. Different results may be obtained by cuing items individually in a nonrandom fashion. Another problem with the directed-forgetting task is that recognition must follow recall. If the order of recognition and recall are reversed, with recognition preceding recall, the inhibited items will be released from inhibition and directed-forgetting effects in recall will not be found. However, this order of task presentation may affect item output. We do not believe that these methodological problems are great enough to warrant not using this methodology for future investigations. However, one should be aware of such downfalls before utilizing one of these techniques. Future research using directed-forgetting can also shed light on the inhibi-
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tion mechanism. Differences in directed-forgetting performance in the ‘‘only’’ and blocked-cued directed-forgetting tasks would be a place to begin investigations of the retrieval inhibition mechanism. Both tasks utilize blocked cuing to produce directed-forgetting effects. The difference in the two tasks is in the placement of the forget cue. Because the forget cue is placed between the blocks of items presented in a blocked cuing task, processes in addition to retrieval inhibition are probably affecting item recall in this task. The role of other cognitive processes in retrieval inhibition could lead to insights into the mechanism of inhibition. In addition, both cuing methods rely on the presentation of items in sets or groups to produce retrieval inhibition. The influences of set differentiation of the TBR and TBF items on directed-forgetting could give insight into the conditions necessary for efficient retrieval inhibition. Another goal of future work should be to assess the multiple versus single process nature of the inhibition mechanisms. Is inhibition in behavior distinct developmentally and physiologically from inhibition within cognition? Are there different forms of inhibition that function within motor, perceptual, and linguistic domains? Or is inhibition a single process that is early developing and that can function in any task that is within the capacities of a child? Behavioral or motoric abilities develop early in life. Cognitive, perceptual, and linguistic abilities develop later. The behavioral and motoric forms of inhibition develop earlier than the cognitive, perceptual, and linguistic forms of inhibition (Dempster, 1993). What may be producing these developmental patterns is that inhibition is developed and is being applied to the areas of mastery in the child. Alternatively, evidence for the multiple process view comes from recent work by Diamond (1991b). She suggests that tasks that require inhibition and working memory may be controlled by the dorsolateral prefrontal cortex, whereas other types of inhibition are not controlled by this region of the brain. This argument points to the potential distinctiveness of inhibition tasks which involve memory from inhibition found in other domains. Finally, the directed-forgetting task can also be used to shed light in more applied areas. For example, there is a growing body of literature on the role of repressed memories form childhood in eyewitness testimony (Ceci & Bruck, 1995). Repressed memories are memories from earlier in life that resurface following a period during which the memory was not retrievable. These memories are thought to be relatively complete and accurate. However, there is evidence to suggest that memories from earlier in life that are suddenly recalled may not be repressed memories at all. It is doubtful that a type of memory exists that can be completely blocked from consciousness and that is not affected by traditional forgetting mechanisms such as interference, development, and decay (Ceci & Bruck, 1995). Instead, memories that are labeled as being previously ‘‘repressed’’ could be false memo-
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ries with no related memory initially encoded. The memory retrieved could have been encoded during investigative interviews or therapy. Alternately, repressed memories could be memories that have been suppressed or inhibited. It is the suppressed memories that directed-forgetting can be a useful tool in investigating because suppressed memories should be able to be released from inhibition. The ‘‘only’’ and blocked-cued versions of the directed-forgetting task can be used to investigate the concept of a ‘‘release from inhibition.’’ Previous research has suggested that the best method of releasing a thought from inhibition is by re-presenting the previously inhibited thought to participants (Basden et al., 1993; Bjork, 1989; Epstein & Wilder, 1972; Geiselman & Bagheri, 1985; Geiselman et al., 1985; Reed, 1970). An ‘‘only’’ or blocked-cued directed-forgetting task could be used to implant memories that are then inhibited. Weeks, months, and years later, participants could be re-presented memories that had been previously inhibited, along with memories that were not previously inhibited (i.e., foil memories). The participants’ precision in correctly identifying the previously inhibited memories could give us insight into the likelihood that an inhibited or suppressed thought can be released with accuracy. In addition, previous research has found that both encoding and retrieval manipulations affect the quality of a stored trace (Brainerd et al., 1990). Certain methods of encoding the inhibited thought, as well as certain methods of releasing the inhibited thought from memory, may be superior in terms of retrieving an accurate memory. Children of different ages could also be tested to determine the accuracy of releasing thoughts from inhibition that have been inhibited at different ages of encoding. Recall that the cognitive inhibition theory predicts that children at young ages cannot inhibit information. This would suggest that young children would be good witnesses because all of their memories should be uninhibited. However, there is growing evidence that efficient inhibition may be earlier developing than predicted by the inefficient inhibition hypothesis (Tipper & MacLaren, 1990; Tipper et al., 1989). This suggests that even young children can inhibit memories. There is also evidence that children at younger ages forget information more quickly than children at older ages and adults (Brainerd et al., 1990; Howe, 1991; Howe, Kelland, Bryant-Brown, & Clark, 1992). Inhibited memories, just like any other memory, should be affected by forgetting. This suggests that inhibited memories, as well as uninhibited memories in children, are less stable over time than inhibited or uninhibited memories in adults. Therefore, the directed-forgetting task can be used to investigate the ages at which information can be inhibited by children of different ages, as well as how developmental trends in forgetting affect children’s ability to release that information from inhibition. Participants could also be asked to recall the previously inhibited memo-
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ries implanted through a directed-forgetting task without the re-presentation of previously inhibited memories. This type of test could be conducted to determine the likelihood that memories encoded at certain ages, and memories that are years old, resurface without additional help. It could also help us to learn about the time frame in which previously inhibited memories can resurface in a close to accurate form. Errors in recall should also be analyzed to determine the likelihood that false memories are retrieved. By comparing the type of false memories retrieved with the initial event, we might also be able to determine the relationship of the false memories to the actual event. Memories may be recovered that are false, but fall within a ‘‘theme’’ that was alive during an individual’s childhood. REFERENCES Basden, B. H., Basden, D. R., & Gargano, G. J. 1993. Directed-forgetting in implicit and explicit memory tests: A comparison of methods. Journal of Experimental Psychology: Learning, Memory, and Cognition, 19(3), 603–616. Bjork, R. A. 1989. Retrieval inhibition as an adaptive mechanism in human memory. In H. L. Roediger & F. I. M. Craik (Eds.), Varieties of memory and consciousness. Hillsdale, NJ: Erlbaum. Bjork, R. A. 1972. Theoretical implications of directed forgetting. In A. W. Melton & E. Martin (Eds.), Coding processes in human memory. Washington, DC: Winston. Bjork, R. A. 1970. Positive forgetting: The noninterference of items intentionally forgotten. Journal of Verbal Learning and Verbal Behavior, 9, 255–268. Bjork, R. A., & Geiselman, R. E. 1978. Constituent processes in the differentiation of items in memory. Journal of Experimental Psychology: Human Learning and Memory, 4(4), 347–361. Bjork, R. A., & Woodward, A. E. 1973. Directed-forgetting of individual words in free recall. Journal of Experimental Psychology, 99(1), 22–27. Bjorklund, D. F., & Harnishfeger, K. K. 1990. The resources construct in cognitive development: Diverse sources of evidence and a theory of inefficient inhibition. Developmental Review, 1, 48–71. Block, R. A. 1971. Effects of instructions to forget in short-term memory. Journal of Experimental Psychology, 89(1), 1–9. Brainerd, C. J., & Reyna, V. F. 1993. Domains of fuzzy trace theory. In M. L. Howe & R. Pasnak (Eds.), Emerging themes in cognitive development: Vol. 1. Foundations. New York: Springer-Verlag. Brainerd, C. J., Reyna, V. F., Howe, M. L., & Kingma, J. 1990. The development of forgetting and reminiscence. Monographs of the Society of Research in Child Development, 55 (Serial No. 222). Bray, N. W., & Ferguson, R. P. 1976. Memory strategies used by young normal and retarded children in a directed forgetting paradigm. Journal of Experimental Child Psychology, 22, 200–215. Bray, N. W., Hersh, R. E., & Turner, L. A. 1985. Selective remembering during adolescence. Developmental Psychology, 21(2), 290–294. Bray, N. W., Justice, E. M., & Simon, D. L. 1978. The sufficient conditions for directed forgetting in normal and educable mentally retarded adolescents. Intelligence, 2, 153– 167.
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Bray, N. W., Justice, E. M., & Zahm, D. N. 1983. Two developmental transitions in selective remembering strategies. Journal of Experimental Psychology, 36, 43–55. Bruce, D., & Papay, J. P. 1970. Primacy effect in single-trial free recall. Journal of Verbal Learning and Verbal Behavior, 9, 473–486. Case, R. 1985. Intellectual development: Birth to adulthood. New York: Academic Press. Case, R., Kurland, M., & Goldberg, J. 1982. Operational efficiency and the growth of shortterm memory span. Journal of Experimental Child Psychology, 33, 386–404. Cassel, W. S., & Bjorklund, D. F. 1995. Developmental patterns of eyewitness memory and suggestibility: An ecologically based short-term longitudinal study. Law and Human Behavior, 19(5), 507–532. Ceci, S. J., & Bruck, M. 1995. Jeopardy in the courtroom: A scientific analysis of children’s testimony. Washington, DC: APA. Clark, J. M., & Johnson, C. J. 1994. Retrieval mechanisms in the development of instance and superordinate naming of pictures. Journal of Experimental Child Psychology, 57, 295–326. Cummings, E. M., & Bjork, E. L. 1983a. Perseveration and search on a five-choice visible displacement hiding task. Journal of Genetic Psychology, 142, 283–291. Cummings, E. M., & Bjork, E. L. 1983b. Search behavior on multi-choice hiding tasks: Evidence for an objective conception of space in infancy. International Journal of Behavioral Development, 6, 71–87. Davis, J. C., & Okada, R. 1971. Recognition and recall of positively-forgotten items. Journal of Experimental Psychology, 89, 181–186. Dempster, F. N. 1993. Resistance to interference: Developmental changes in a basic processing mechanism. In M. L. Howe & R. Pasnak (Eds.), Emerging themes in cognitive development, Vol. 1: Foundations. New York: Springer-Verlag. Diamond, A. 1991b. Frontal lobe involvement in cognitive changes during the first year of life. In K. R. Gibson & A. C. Petersen (Eds.), Brain maturation and cognitive development. New York: Aldine de Gruyter. Diamond, A. 1991a. Neuropsychological insights into the meaning of object concept development. In S. Carey & R. Gelman (Eds.), The epigenesis of mind: Essays on biology and knowledge. Hillsdale, NJ: Erlbaum. Diamond, A., Cruttenden, L., & Neiderman, D. 1994. AB with multiple wells: 1. Why are multiple wells sometimes easier than two wells? 2. Memory or Memory 1 Inhibition. Developmental Psychology, 30(2), 192–205. Elmes, D. G., Adams, C., & Roediger, H. L. 1970. Cued forgetting in short-term memory: Response selection. Journal of Experimental Psychology, 86, 103–107. Engle, R. W. 1996. Working memory and retrieval: An inhibition-resource approach. In M. Marschark (Ed.), Working memory and human cognition. New York: Oxford. Engle, R. W., Conway, A. R. A., Tuholski, S. W., & Shisler, R. J. 1995. A resource account of inhibition. Psychological Science, 6(2), 122–125. Epstein, W. 1972. Mechanisms of directed-forgetting. In G. H. Bower (Ed.), The psychology of learning and motivation. New York: Academic Press. Epstein, W. 1969. Poststimulus output specification and differential retrieval from short-term memory. Journal of Experimental Psychology, 82(1), 168–174. Epstein, W., & Wilder, L. 1972. Searching for to-be-forgotten material in a directed-forgetting task. Journal of Experimental Psychology, 95, 349–357. Epstein, W., Massaro, D. W., & Wilder, L. 1972. Selective search in directed forgetting. Journal of Experimental Psychology, 94(1), 18–24.
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