Repetition Priming and Frequency Attenuation in Lexical Access

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Repetition priming effects in lexical decision tasks are stronger for low- ... This hypothesis is supported by the demonstration of constant repetition effects.
Copyright 1984 by the American Psychological Association, Inc.

Journal of Experimental Psychology: Learning, Memory, and Cognition 1984, Vol. 10, No. 4, 680-698

Repetition Priming and Frequency Attenuation in Lexical Access Kenneth I. Forster and Chris Davis Monash University, Victoria, Australia Repetition priming effects in lexical decision tasks are stronger for low-frequency words than for high-frequency words. This frequency attenuation effect creates problems for frequency-ordered search models that assume a relatively stable frequency effect. The suggestion is made that frequency attenuation is a product of the involvement of the episodic memory system in the lexical decision process. This hypothesis is supported by the demonstration of constant repetition effects for high- and low-frequency words when the priming stimulus is masked; the masking is assumed to minimize the influence of any possible episodic trace of the prime. It is further shown that long-term repetition effects are much less reliable when the subject is not required to make a lexical decision response to the prime. When a response is required, the expected frequency attenuation effect is restored. It is concluded that normal repetition effects consist of two components: a very brief lexical effect that is independent of frequency and a long-term episodic effect that is sensitive to frequency. There has been much recent interest in the fact that in a lexical decision experiment, where subjects are required to classify letter strings as words or nonwords, there is a substantial increase in both the speed and the accuracy of classification for words that are presented more than once during the experiment, even though considerable time may have elapsed between successive presentations (Forbach, Stanners, & Hochhaus, 1974; Kirsner & Smith, 1974; Scarborough, Cortese, & Scarborough, 1977). This phenomenon is referred to as the repetition effect. There are basically two different approaches to the repetition effect. On the one hand, it is seen as the product of a temporary modification to the process of lexical access (e.g., Forbach et al., 1974). As a result of recent activation, the lexical representation of a word is left in a state of increased accessibility. This priming effect can then be used as a powerful diagnostic tool for analyzing the

structure of the mental lexicon and the mechanisms of access (e.g., Morton, 1979, 1980; Scarborough, Gerard, & Cortese, 1979). On the other hand, it can be seen as a useful technique for studying memory processes (Jacoby & Dallas, 1981; Jaqoby & Witherspoon, 1982). On this view, the first presentation of a word (the prime) establishes an episodic memory trace mat is contacted when the same word (the target) is presented again. In some way this trace produces a facilitative effect on perceptual tasks such as lexical decision or accuracy of report with brief exposure. The important aspect of this account for present purposes is that the repetition effect can be explained without assuming that the lexical representation of the target word is altered in any way. These two different approaches can lead to very different interpretations of the same data. Consider, for example, the problem of cross-modal transfer. Morton (1979, 1980) claims that there is no repetition effect at all when the two presentations of the target word are in different modalities. Because Morton This article is based in part on research reported by the second author as part of an honors thesis at Monash treats the repetition effect as a purely lexical University. The research was supported by a grant from effect (i.e., as occurring totally within the the Australian Research Grants Scheme. mental lexicon), he is forced to postulate that The authors wish to thank Don Mitchell, Di Bradley, each word has a separate lexical representaand Don Thomson for extensive discussion and comments. Requests for reprints should be sent to Kenneth I. tion (logogen) for each input modality. Hence, Forster, Department of Psychology, Monash University, auditory presentation of a word leads to Clayton, Victoria, Australia 3168. residual activation in its auditory input lo680

REPETITION PRIMING

gogen but not in its visual input logogen. However, if repetition is seen as the result of the influence of episodic memory traces, then quite different conclusions are possible. For example, it could be argued that when the target word is presented visually, then only the memory traces of previous visual presentations can produce a facilitative effect. Hence, the lack of cross-modal transfer may have no implications at all for the structure and organization of the mental lexicon. The same arguments apply to the fact that there is no transfer from picture naming to lexical decision. That is, saying "dog" in response to a picture of a dog produces no facilitation for subsequent lexical decisions on the word dog (Scarborough et al., 1979). On a purely lexical interpretation, this means that quite different logogens must be activated by pictures and by words. But on an episodic interpretation, this result may mean only that the episodic trace of the picture naming experience has no effect in the lexical decision situation, either because the episodic trace is not activated by seeing the word dog, or because it is not activated rapidly enough, or because it is simply irrelevant. Similar problems arise in the interpretation of what is referred to here as the frequency attenuation effect. As shown by Scarborough et al. (1977), low-frequency words benefit far more from repetition than do high-frequency words. If we adopt a purely lexical interpretation of this effect, then the conclusion is that the accessibility of a lexical representation is a highly dynamic, labile property. This is not what would be expected from lexical search theories (Becker, 1979; Forster, 1976; Stanners & Forbach, 1973), which assume that the frequency effect reflects reasonably static organizational properties of the mental lexicon, with high-frequency words being located earlier in the search path than lowfrequency words. Such theories would have to be modified substantially to accommodate the frequency attenuation effect. However, if the repetition effect is not a true lexical effect, this may not be necessary. For example, it is well known that in tests of recognition memory (old-new classification), subjects are more certain whether they have recently seen a low-frequency word than a high-frequency word (e.g., Glanzer & Bowles, 1976; Gregg,

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1976; Scarborough et al., 1977). This advantage for low-frequency words in episodic tasks may be directly responsible for the frequency attenuation effect, perhaps because the episodic traces of low-frequency words can be contacted more efficiently. From the viewpoint of theories of lexical access, it is therefore necessary to assess whether any particular property of the repetition effect reflects alterations to the organization of lexical entries or whether it reflects influences from episodic memory traces that are quite external to the lexical processor itself. It has been argued that episodic influence can be ruled out on the ground that variables that normally affect the strength of the episodic trace do not alter the repetition effect (e.g., Jacoby & Dallas, 1981; Jacoby & Witherspoon, 1982; Scarborough et al., 1977). However, these experiments might have succeeded only in showing that the way in which an episodic trace is utilized might vary across tasks. For example, it could be that the lexical decision task is much more sensitive to the existence of episodic memory traces than is an episodic task such as old-new classification, and hence, trace strength is less relevant in the lexical decision task. Although this evidence in inconclusive, there is clear evidence that episodic factors are sometimes involved. Jacoby (1983) found that as the proportion of words common to the study and test lists was increased, the magnitude of the repetition effect increased. This is quite incompatible with a purely lexical interpretation, because the only necessary and sufficient condition for a repetition effect should be the previous activation of lexical representations. More compelling is the evidence produced by Feustal, Shiffrin, and Salasoo (1983). They pointed out that a lexical view predicts no repetition effect for nonwords because nonwords do not have lexical representations, by definition. However, some studies have reported small effects for nonwords (e.g., Besner & Swan, 1982; Kirsner & Smith, 1974; Scarborough et al., 1977), although others have not (e.g., Forbach et al., 1974). Feustal et al. pointed out that small or non-existent effects may be expected because accessing an episodic trace may well inhibit the no response required for nonwords. By designing tasks that eliminate this prob-

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lem, they were able to demonstrate clear and reliable repetition effects for nonwords. This evidence suggests at least that the repetition effect is a composite effect. However, there is also evidence for a stronger conclusion, namely, that there is no purely lexical repetition effect. Oliphant (1983) compared the repetition effects in two situations. In the first condition, subjects made lexical decisions on the same word on two separate occasions, and normal repetition effects were obtained. In the second condition, the subjects were asked to read the instructions for the experiment aloud. Some of the words in the instructions were then presented for lexical decision. No repetition effect was observed, despite the fact that the entries for these words must have been-accessed during the reading of the instructions. Oliphant's conclusion was that the repetition effect was not an automatic effect of recent exposure to a word, but depended on the subject's awareness of repetition and the development of strategies to speed up processing of repeated words. Once the possibility of episodic involvement is conceded, we can no longer be certain of any of the properties of a purely lexical repetition effect because there is no way to decide which properties are produced by the episodic component. The only way to remedy this situation is to attempt to minimize the contribution of episodic factors and to see what properties remain. The aim of the present series of experiments is to examine the frequency attenuation effect under these conditions. One way to minimize episodic influences is by masking the priming stimulus (the first presentation) so that subjects are unable either to report it or to recognize it. Although this does not necessarily mean that no episodic trace of the prime exists, it does imply that it is relatively inaccessible. Hence, any subsequent effect of this prime on the processing of the same word would be relatively free of episodic contamination. Precisely the same lope was successfully applied by Balota (1983) to the problem of contextual effects in episodic recognition. Balota was able to show that the inhibiting effects of a change of context on episodic recognition were absent when the initial context was masked, even

though this masked context produced reliable semantic priming effects. Masked repetition effects were successfully obtained by Evett and Humphreys (1981). In these experiments, a sequence of four brief stimuli was presented: mask; prime, target, mask. The prime and the target were either the same word or were different, but they were always presented in a different case. Pattern masks were used, and performance was measured by accuracy of report of the target stimulus. Significant repetition 'effects were observed, despite the fact that the prime and target stimuli were in different cases. The first experiment employed an adaptation of the Evett and Humphreys technique to study frequency attenuation without episodic contamination. Instead of using accuracy of report of a masked target as the dependent measure, lexical decision time was used, and the target item was freely available. If the frequency attenuation effect is a genuine lexical effect, then elimination of the episodic trace of the prime should have no effect, that is, masked repetition effects should also be greater for low-frequency words. Experiment 1 Each trial consisted of a sequence of three stimuli; the first two were in lowercase letters, and the third was in uppercase letters. The third stimulus was the target stimulus that had to be classified as a word or as a nonword. The second stimulus was the prime and was either identical to the target stimulus (but in lowercase letters) or was different. The first stimulus was always a neutral word, unrelated to any other in the sequence. Both the first and third items were presented for 500 ms, whereas the prime was presented for 60 ms. The only purpose of the first word was to act as a forward mask for the prime. A pilot experiment using this technique established that words preceded by an identical prime in a different case were responded to 35 ms faster than were words preceded by a nonidentical prime. There was no repetition effect for nonwords; the difference was 4 ms in the wrong direction. The durations of the three stimuli were chosen by the experimenters so that the prime appeared invisible to them and the subjects of the pilot study. To check this, two further pilot studies were

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conducted to assess the amount of informa- sequential display of the three members of a triad; each member was displayed in the center of the screen. The tion available to awareness. In the first of durations the first and third members was 500 ms, these additional pilot studies, subjects were whereas theof second member was displayed for 60 ms. told that the sequence in fact consisted of Each member was displayed immediately after the prethree stimuli. Their task was.merely to guess ceding member. The subject was instructed to classify the item in whether the second item contained the same uppercase (the third member) as a word or a sequence of letters as the third item. Twelve nonword. Itletters was explained that this would always be the subjects were tested with a set of 60 words final member, but no mention was made of the number and 60 nonwords. The overall error rate was of items in the total sequence. Each trial was initiated 41%, Some subjects reported that they occa: by the subject, and feedback was provided concerning both accuracy and speed of response. Subjects indicated sionally managed to see one letter in the their decisions by a selective button press, with the prime, and if the target stimulus contained preferred hand used for yes decisions. A different pseuthat letter, they responded same. This might dorandom sequence was prepared for each subject, and have accounted for the slightly better than a set of 10 practice items was included. Subjects were either the first or the second set of item's, so that chance performance. In the second additional given no test pilot study, the same materials were used, subject. item was responded to more than once by any but subjects were required to guess whether Subjects. A total of 28 volunteer undergraduates the second stimulus was a word. Twelve sub- served as subjects. Any subject making more than 20% jects were used, and it is worth noting that errors was rejected. No subject had participated in any all subjects commented on the extreme diffi- of the pilot studies. culty, if not absurdity, of the task. In fact, the overall error rate was 50%, and no subject Results made fewer than 45% errors. Hence, it seems In this experiment, as in subsequent exsafe to conclude that very little precise information about the prime as a whole was periments, the effects of outliers were curtailed by cutoffs established 2 standard deviations available for conscious recall. above and below the mean of each subject. Data from trials on which an error occurred Method were discarded. Separate analyses of the subMaterials and design. The target items consisted of 60 words and 60 legal nonwords, Half of the words were ject and item means were carried out and high-frequency words, chosen at random from a frequency were combined to form F'min values according range of 40-60 occurrences per million (Kucera & Francis, to the procedure recommended by Clark 1967). Half were low-frequency words, chosen at random from a frequency range of 1-2 occurrences per minion. (1973). Mean lexical decision times and error rates These words were all judged by the experimenters to be within the working vocabulary of the typical subject (e.g., for both words and nonwords are shown in ADORE, HEAVE, ARID, FROCK). A ,S6t Of 120 triads W8S Table 1. The results for the words were constructed; the third member was one of the above analyzed in a 2 X 2 X 2 factorial design; the target items in uppercase letters. The second member was either the same letter sequence as the third or was a factors were groups (subject groups in the different sequence of the same length. In this latter case, analysis of subject means, item groups in the it was a word if the target item was a word, otherwise it analysis of item means), frequency (high vs. was a nonword. The second member was presented in low), and repetition (repeated vs. nohrelowercase letters, and hence was physically different from peated). the third in all triads. The first member was a randomly For words, lexical decision times were faster chosen dummy word in lowercase letters. All targets were (598 ms) if they were immediately preceded 4-?6 letters in length. A second set of 120 triads was constructed that had by the same word than if they were not (640 the same target items as the first but had different ms); this effect was significant, F' (l, 56) = min preceding items. These triads were constructed so that if a triad in the first set contained a repetition (e.g., absent 15.41, p < .001. There was also a significant circle CIRCLE), its corresponding member in the second main effect of frequency; high-frequency set did not (e.g.,; beam device CIRCLED and vice versa. words were classified faster (573 ms) than Thus, it was possible to examine performance on the were low-frequency words (665 ms), F'mi«(l, same set of items in both the repeated and nonrepeated 64) = 23.66, p < ,001. However, there was conditions. • Procedure, Items were presented on a computer- no significant interaction between these main controlled video display. Each trial consisted of the effects; the repetition effect for high-frequency

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KENNETH I. FORSTER AND CHRIS DAVIS

Table 1 Experiment 1: Mean Lexical Decision Times (KT in Milliseconds) and Percentage of Errors for Repeated and Nonrepeated Items Using Masked Primes Item type High-frequency words Repeated

Example

absent avoid

RT

error

550

2.9

595

4.5

45

1.6

646

15.3

684

21.2

38

5.9

687

6.9

679

6.0

AVOID

Nonrepeated

bullet taste AVOIP

Repetition effect Low-frequency words Repeated

cloud heave HEAVE

Nonrepeated

cape exalt HEAVE

Repetition effect Nonwords Repeated

brass tovid TOVID

Nonrepeated

. complete astol TOVID

Repetition effect

-8

-0.9

words (45 ms) was slightly larger than the effect for low-frequency words (38 ms, F'min < 1). Analysis of the error rates for words shows the expected higher error rate for low-frequency words, and although there is a trend toward fewer errors for repeated items, this effect was not significant, FJnin(l", 68) = 3.25, p > .05. The Frequency X Repetition interaction was not significant. The results for nonwords were analyzed in a 2 X 2 design; the factors were Groups and Repetition. It is clear that nonwords do not show a repetition effect, because repeated nonwords took slightly longer to classify than did nonrepeated nonwords, and repeated nonwords produced slightly more errors. Neither of these effects was significant (tfnta < I)-

Discussion The results of this experiment confirm the findings of Evett and Humphreys (1981) in demonstrating that significant repetition effects can be obtained even when the prime is heavily masked and is unavailable for con-

scious report. In addition, the results suggest that the nature of the priming effect is different from that observed in more conventional repetition studies where the priming stimulus is not masked (e.g., Scarborough et al., 1977). The difference is that equal priming effects are observed for both high- and low-frequency words. The primary purpose of masking the prime was to prevent the possibility that episodic traces of the prime might influence the decision process. If this goal has in fact been achieved, then the results suggest that the attenuation of the frequency effect produced by repetition can be attributed to episodic factors. Before we consider the implications of this conclusion, there are a number of alternative interpretations that should be considered. First, it should be noted that Evett and Humphreys (1981) interpreted their findings in terms of graphemic priming effects. Logogens are assumed to be partially activated by the presence of letters in specific positions, regardless of visual format (case). Hence, the logogen for STATE will be activated by prior exposure to a similar word, such as STARE, and even by prior exposure to a nonword such as STAFE. This increase in activation may well be a very temporary phenomenon, only detectable with very short intervals between the prime and the target. It may also have nothing to do with the normal repetition effects observed in experiments employing much longer intervals with many intervening items, that is, the repetition effect observed in this experiment might be a much more limited phenomenon. In the extreme case, it could even be suggested that the priming action is limited merely to the detection of the graphemic form of the test stimulus, and hence, it is not at all surprising that equal priming effects are observed for high- and low-frequency words. In order to show that the effects observed in this experiment are genuine word-repetition effects, it is therefore necessary to show that the priming is not the result of a letterrepetition effect or of a graphemic priming effect. The letter-repetition interpretation seems unlikely, because this should have produced priming effects for nonwords as well as words. However, this evidence is irrelevant

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to the graphemic priming interpretation, because this depends on the existence of a logogen corresponding to the target stimulus. The only way to test this hypothesis is to repeat the first experiment using graphemically similar prime-target word pairs. If no facilitation is produced, then the conclusion that we are dealing with a genuine wordrepetition effect is strengthened. The next experiment was designed to examine this issue. Experiment 2 The priming effect observed in the first experiment might have been a genuine wordrepetition effect in the sense that it was due to the repeated access of the same lexical entry. Alternatively, it might simply have arisen from the graphemic overlap between the prime and the target; this overlap could have produced a letter-repetition effect, because the same letters had to be processed for both stimuli, or it could have produced a graphemic priming effect, in which the processing of the prime produces activation in the logogens of all graphemically similar words. If either of these alternative explanations is correct, then it should be possible to demonstrate transfer effects between similar primes and targets such as lump-UMP, as shown by Evett and Humphreys (1981) in a tachistdscopic accuracy task. As in the first experiment, a lexical decision task was used, and the prime was masked by its surrounding context. Priming effects for both word and nonword targets was examined.

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(e.g., bend-BOND, peck-PACK, dusk-oiSK). For the dissimilar pairs, the prime was chosen from the same frequency range as the target. For nonwords, the prime was always either a similar nonword (e.g., mulp-MiLP, cusk-cisic, tasm-TiSM), or a dissimilar nonword (e.g., leng-QRAD, trie-STOL, nout-SAMP). As in Experiment 1, these pairs were preceded by a dummy word. The lengths of all three items in each triad were the same (4 letters). Again, two sets of materials were constructed so that targets preceded by a similar prime in one set were preceded by a dissimilar prime in the other, and vice versa. Procedure. The method of presentation and testing was exactly the same as in Experiment 1. Subjects. A total of 24 undergraduate volunteers who had not participated in any of the preceding experiments was used. Half were run with one set of materials, and half were run with the counterbalanced version.

Results The mean lexical decision times for the target items are shown in Table 2. These results show that there is a difference of only 1 ms (in the wrong direction) for the word targets as a function of similarity, whereas for nonword targets, the effect is only 7 ms. Neither of these differences was significant (^"min < 1). There were also no significant effects of similarity on the error rates, Further analysis of the results for the similar words condition showed no effect of the frequency of the prime. Words preceded by a similar prime of higher frequency were responded to slightly slower (528 ms) than were words preceded by a similar prime of lower frequency (520 ms), but this difference was not significant (F'mia < 1).

Discussion

These results indicate that graphemic overlap between the prime and the target produces Materials and design. A total of 60 triads was con- very little impact on lexical decision times structed as in Experiment 1 except that instead of having for the target. This indicates that the priming half of the primes identical to the target, they differed from the target by one medial letter. Half of the targets effect observed in Experiment 1 was not due were words chosen from a frequency range of 20-30 either to a letter repetition effect or to graoccurrences per million; half were legal nonwords. Half phemic priming. In order for the prime to of the word targets were preceded by a briefly presented influence lexical decisions, the target must be dissimilar prime that had no more than one letter in the same position as the target (e.g., cure-MALE, bowl-piLE, a word (because no priming occurred for tire-LOST), The remaining targets were preceded by a nonwords in Experiment 1), and the prime similar prime in which only one letter differed from the must be identical to the target. These proptarget. Because it was difficult to control the frequency erties appear to meet the requirements of a of such similar pairs precisely, it was decided to manipulate genuine word-repetition effect. this variable systematically. Half of the similar primes It should be noted that these results are in were higher in frequency than the target (e.g., line-LANE, past-POST, hall-HELL), and half were lower in frequency sharp contrast to those of Evett and Hum-

Method

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KENNETH I. FORSTER AND CHRIS DAVIS

Table 2

Experiment 2: Mean Lexical Decision Times (RT in Milliseconds) and Percentage of Errors for Items Preceded by Graphemically Similar and Dissimilar Masked Primes Item type

Example

RT

error

Words Similar prime

harm lack

524

11.0

523

14.2

1

3.2

552

7.1

559

2.1

7

-5.0

LOCK

Dissimilar prime Priming effect Nonwords Similar prime

harm bowl LOCK

dirt nila NELA

Dissimilar prime Priming effect

dirt wold NELA

it seems much less likely that such a conflation of prime and target would occur. Because the only effect observed with the lexical decision task is an effect of identical repetition, we must assume that the same effect would have occurred in Evett and Humphreys' experiment. However, the remaining effects in their experiment may be attributable to conflation. It is also worthwhile noting that Feustal et al. (1983) reported small but significant priming effects produced by graphemic overlap of the prime and target. In this case, however, the prime and target were separated by a number of intervening items, so rather different mechanisms must be involved. They also used an identification accuracy task, and it may be that graphemic similarity effects are restricted to this type of task. The results of this experiment are also relevant to studies dealing with conflicting graphemic and phonemic overlap. While Meyer, Schvaneveldt, and Ruddy (1974) found no significant facilitation for pairs such as BRIBE-TRIBE, subsequent investigators have reported such effects (Hillinger, 1980; Shulman, Hornak, & Sanders, 1978). One possible reason for the discrepancy may be that the location of the difference between the prime and target varies (medial in the present case, initial in all others). However, a more: likely reason is that strategic factors play a role in these experiments but are most unlikely to be involved in the current experiment because presumably, awareness of the nature of the prime would be a necessary precondition for the development of a successful strategy that exploited the relation between the prime and the target.

phreys (1981). They found that similar primes produced facilitation for target identification, whether the prime was a word or a nonword. The most obvious difference between the experiments is that Evett and Humphreys used an accuracy response measure, and the target word also was masked. One possible consequence of this is that the subjects might have combined information from the prime and the target. For example, suppose that the target word is STATE, and the subject manages to identify only the last three letters. Suppose, also, that he has identified the first two letters of the prime as st. If these partial identifications are combined, the correct word is produced, whether the prime was the identical word STATE, a similar word STARE, or even a similar nonword STAFE. Such a combination Experiment 3 strategy need not, of course, be intentional. This interpretation is best supported by The repetition effect observed in Experithe fact that priming was produced by gra- ment 1 with masked primes was insensitive phemically similar nonwords. Furthermore, to word frequency, that is, there was no as the authors noted, subjects occasionally attenuation of the frequency effect for remade errors by inserting letters from the peated items. This result suggests that when prime into the target (e.g., responding STRING episodic involvement in the repetition effect to the prime-target pair yoing-STRiPE). The is minimized, frequency attenuation effects fact that this involves a change of case simply are also minimized. indicates that subjects are using abstract This conclusion would be strengthened if properties rather than physical properties. it could be shown that frequency attenuation However, in a lexical decision task, where effects are found for the same experimental the target is not masked but is freely available, items when the prime is not masked, and the

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repetition effect is produced in the normal way. This is the aim of the present experiment. The design of the experiment consisted of two phases. In Phase 1, words and nonwords were-presented in lowercase letters for lexical decision. In Phase 2, the same items were presented again, along with an equal number of items that appeared for the first time. All items in Phase 2 were presented in uppercase letters, so that there was a shift in case between the first and second presentations. Although changes in the physical format of the stimuli are not particularly critical for the repetition effect (Feustal et al, 1983; Scarborough et al., 1977), this procedure makes the conditions of this experiment more comparable with those of Experiment 1, where primes and test stimuli also differed in case. The two-phase procedure was chosen in preference to a single list design with intralist repetition in order to minimize possible strategic effects. In the two-phase design, all primes will have been presented before any repetition occurs, and hence the encoding of the primes cannot be affected by the subject's perception of repetition. However, in a single list design, the subjects will have noted the fact that items are repeated quite early in the list, and hence might attend more closely to subsequently presented primes.

Method Materials and design. The experimental items were the same as those used in Experiment t. Throughout the experiment, subjects were presented with a single word or nonword for lexical decision. The experiment consisted of two phases. In Phase 1, subjects were presented with 15 high-frequency words, 15 low-frequency words, and 30 nonwords, all in lowercase letters. In Phase 2, the same items were presented again in uppercase letters, along with an equal number of words and nonwords that appeared for the first time. Two sets of materials were constructed. For both sets, Phase 2 consisted of the' same set of 120 items. Half of these items were randomly chosen for inclusion in Phase 1 for the first set, and the other half were chosen for the second set. Thus, materials were counterbalanced across the Repetition factor. From the subject's point of view, the division of the experiment into phases was to clearly separate the lowercase items from the uppercase items. Subjects. A total of 28 volunteer undergraduates (the same number as in Experiment 1) served as subjects and were paid. Subjects were assigned to one set of materials or the other in the order of their appearance at the laboratory.

Table3 Experiment 3: Mean Lexical Decision Times (RT in Milliseconds) and Percentage of Errors for Words and Nonwords in Phase 2 Preceded by Primes in Phase 1

Item type High-frequency words Repeated Nonrepeated Repetition effect Low-frequency words Repeated Nonrepeated Repetition effect Nonwords Repeated Nonrepeated Repetition effect

RT

% error

50L 531 30

2.9 4.8 1.9

552 615 63

12.4 21.9

606 598 -8

4.3 2.0

9.5

-2.3

Note, Lexical decision required for primes.

Results and Discussion The mean lexical decision times for both words and nonwords in Phase 2 are given in Table 3. The effect of word frequency (68 ms) was significant, F'min(l, 57) = 26.05, p < .001, as was the effect of repetition (47 ms), F'min(l, 40) = 21.56, p< .001. There was also a significant interaction between these main effects, Fmin(l, 44) = 5.06, p < .05; high-frequency words snowed a smaller repetition effect (30 ms) than did low-frequency words (63 ms). However, both of these individual repetition effects were highly significant: for high-frequency words, Fmin(l, 51) = 8.85, p < .01, and for low-frequency words, F'minU, 39)= 17.87, p .05. This suggests that repetition produces a spurious familiarity effect for some subjects but not all subjects. The error results show a very similar pattern. As expected, more errors were made on low-frequency words than were made on highfrequency words, FJninO, 81) = 22.75, p < .001. Repetition reduced the total number of errors for words, Fmin(l, 57) = 6.87, p < .05, and tended to reduce the number of errors for low-frequency words to a greater extent

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KENNETH I. FORSTER AND CHRIS DAVIS

than it did for high-frequency words, although this interaction effect was marginal, F'mm(l, 62) = 3,40, p < .10 (both subject and item analyses were significant). For nonwords, however, the inhibitory effect of repetition was very strong, f"min (1, 60) = 12.36, These results clearly demonstrate that the experimental items used in Experiment 1 produce a frequency attenuation effect when the repetition effect is induced in the standard manner. Hence, the absence of frequency attenuation in Experiment 1 cannot be attributed to item sampling errors nor can it be attributed to a lack of power, because the power of this experiment was designed to be the same as that of Experiment 1. Hence, it seems reasonable to conclude that the procedure of masking the prime is responsible. It may be suggested that masking the prime does not really alter the size of the repetition effect at all but instead prevents access for a proportion of the low-frequency primes, thereby lowering the average repetition effect for low-frequency words from the 63-ms value observed in the present experiment to the value of 38 ms observed in Experiment 1. This value of 38 ms represents a composite value from items where the prime was accessed (each producing a "normal" repetition effect of 63 ms) and from items where the prime was not accessed (producing a repetition effect of zero). Two features of the results suggest that this is not the correct interpretation. First, it would be expected that masking would also reduce the repetition effect for high-frequency words, although not to the same degree. However, the reverse is the case, because the effect for high-frequency words with masked primes in Experiment 1 (45 ms) was greater than in the present experiment (30 ms). Second, it should be the case that for low-frequency words with masked primes, the variances of the decision times for repeated items should be much greater than those for nonrepeated items (because the former are bimodally distributed). To test this hypothesis, the item variances were calculated separately for each subject in Experiment 1. The obtained mean variances were very similar: 160.7 for repeated low-frequency words and 150.6 for nonrepeated low-frequency words (12 of the 28 subjects failed to show this trend). Moreover, when high-fre-

quency words were included as a control, half of the subjects showed, a greater repetition-induced increase in variance for lowfrequency words than they did for highfrequency words, and half showed the opposite effect. Masking the prime was intended to minimize any possible episodic contamination of the repetition effect. If this was the only consequence of masking, then we should infer that frequency attenuation is a byproduct of an episodically mediated process. However, it may be that the procedures of Experiments 1 and 3 also differ in other ways. For example, the delay between the prime and target was only 60 ms in Experiment 1, whereas in this experiment, it could have ranged from 5 min to 10 min. It is therefore possible that frequency attenuation only occurs with long delays between presentations. This possibility cannot be ignored, although it has been argued that the standard repetition effect is quite unaffected by:lag (e.g., Feustal et al., 1983; Jacoby & Dallas, 1981; Scarborough et al., 1977, 1979). In addition, Berger (1980) showed clear frequency attenuation effects when the lag in a standard repetition design was only one item. A more crucial difference between the two experiments is the fact that in the current experiment, subjects were required to make a lexical classification of both the prime and the target, whereas in the first experiment, no specific response to the prime was required (nor was it possible make such a requirement, because the prime was not visible). This raises the interesting possibility that frequency attenuation effects may be restricted to designs that require a specific decision to be made about the prime. This possibility can be examined by repeating the present experiment without requiring the subject to respond in any way to the prime. This was attempted in the next experiment. Experiment 4 The purpose of this experiment was to determine whether the frequency characteristics of the standard repetition effect depend on the type of response that must be made to the prime. The design of this experiment paralleled that of Experiment 3 in that there were two phases: The primes were presented in Phase 1, and the effects of these primes

689

REPETITION PRIMING

were assessed in Phase 2. The only difference between the experiments was that the primes were not presented for lexical decision. Instead, they were presented as part of the context for another target word altogether. So, for example, a subject might have received the following combination: Phase 1: doctor-(annoy)-ANNOY, Phase 2: DOCTOR. In both phases, the task is to make a lexical decision to the target in uppercase letters. The items in Phase 1 were presented under the same conditions as in Experiment 1; the parentheses indicate the masked word. The question is whether the initial experience of doctor as a context item would serve as a prime for later classification of DOCTOR in Phase 2, and whether this effect would be sensitive to frequency. Method The design of this experiment was similar to that of Experiment 3. There were two phases; the primes were presented in Phase 1, and the targets were presented in Phase 2, The materials and procedure for Phase 2 were identical to Experiment 3; 60 words and 60 nonwords were presented for lexical decision. The items in Phase 1 were structured in the same way as the items in Experiment 1: two context items followed by a target item that had to be classified as a word or as a nonword. The duration of the first and last members of this triad was 500 ms; the middle member was presented for 60 ms. The first two members were in lowercase letters, while the third member was in uppercase letters. Half of the words and nonwords presented for lexical decision in Phase 2 were also presented in Phase 1 as an initial member of a triad (for which no response was required). As before, two sets of materials were constructed with a different half of the items repeated across the two phases. In addition, IS of the word targets in Phase 1 were preceded by a masked repetition of the same word in different case, and a further 15 of the word targets were preceded by a different word of the same length. Items repeated in this way in the first set of materials were nonrepeated in the second set, and vice versa. The remaining targets in Phase 1 were irrelevant to the experiment. The instructions to subjects emphasized that in Phase 1, a lexical decision was required only for the item in uppercase letters, but subjects were asked to read the material that preceded this item. It was further explained that in the second phase, only single words, and nonwords would be presented. As in Experiments 1 and 3,28 volunteer undergraduates served as subjects.

Results and Discussion The mean lexical decision times and error rates are given in Table 4 for the word targets

Table 4 Experiment 4: Mean Lexical Decision Times (PT in Milliseconds) and Percentage of Errors for Word Targets in Phase 1 Preceded by a Masked Prime and for Word Targets in Phase 2 Preceded by a Context Prime in Phase 1 Item type Phase 1 word targets: Masked priming Repeated Nonrepeated Repetition effect Phase 2 targets: High-frequency words Repeated Nonrepeated Repetition effect Low-frequency words Repeated Nonrepeated Repetition effect

RT

error

558 610 52

1.0 1.6 0.6

569 577 8

5.0 4.5 -0.5

618 646 28

12.6 19.1 6.5

in Phase 1 preceded by a masked prime and for the word targets in Phase 2 preceded by an earlier presentation of the same word as a context item in Phase 1. Consider first the masked repetition effects during Phase 1. It is shown in Table 4 that primed items were classified faster (558 ms) than were unprimed items (610 ms). This masked repetition effect of 52 ms was highly significant, Fmin(l, 53) = 15.54, p< .001, and confirms the results of Experiment 1. Considering next the results in Phase 2, it can be seen that overall, words repeated across phases were responded to faster (593 ms) than were unrepeated words (611 ms), but this 18-ms effect of•. repetition was only marginally significant, Fmin(l, 76) = 3.57, p< .10 (significant effects were obtained in both the subject and item analyses). Highfrequency words produced faster responses than did low-frequency words, f'min(l, 81) = 25,76, p < .001, but there was no significant Repetition X Frequency interaction (jF'min < 1; nonsignificant results were obtained in both subject and item analyses). Considering the repetition results for high- and low-frequency words separately, there was an effect of only 8 ms for high-frequency words, which was not significant (F'min < 1), while for lowfrequency words, there was a nonsignificant effect of 28 ms, F'mln(l, 37) - 2.77, p > .05 (a significant subject effect was obtained).

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These results appear to indicate that the normal repetition effect is very weak under the conditions of this experiment. The same materials in Experiment 3 produced highly significant repetition effects for both highfrequency words and low-frequency words. Comparison across the two experiments showed that the effect for low-frequency words in Experiment 3 (63 ms) was significantly greater than the corresponding effect with the same items in the present experiment, Fmin(l, 77) = 4.14, p < .05, while the effect for highfrequency words uv Experiment 3 (24 ms) did not differ significantly from the present effect, F'minO, 76) = 2.46,> > .05, although both subject and item analyses did produce significant differences. These results strongly suggest that the magnitude of the repetition effect is influenced by the response required to the prime (especially for low-frequency words). If subjects are merely required to silently read the prime, then the repetition ..effect is weak compared with a condition in which subjects must classify the prime. Unfortunately, this weakening of the effect makes it difficult to answer the question of central interest: Do lowfrequency words show the same repetition effect as high-frequency words? The lack of a significant Repetition Effect X Frequency interaction is not very informative, because there is no clear repetition effect for either word class. Nevertheless, the results of this experiment fit quite well with the general argument that the standard repetition effect is contaminated by episodic factors. If repeated access of the same lexical entry was the sole determinant of repetition effects, then the present experiment should have produced results comparable with those of Experiment 3, which it clearly did not. It seems that the only way to resist this argument is to argue that subjects did not necessarily process the context words in Phase 1 and hence did not access the relevant entries. But if this were the case, it would be hard to explain why there was such a strong masked repetition effect for the target items in Phase 1 (if the masked item was processed enough to have an effect, the much more visible context item should have been processed also). The failure to find a clear repetition effect using nontarget primes is consistent with the findings of Oh'phant

(1983), who failed to find repetition effects when the primes were presehted as part of the instructions for the experiment. This result implies that subjects need to perceive the primes as somehow relevant; to task performance before a strong repetition effect occurs. It would perhaps be premature to conclude from these experiments that there is no repetition effect with nontarget priming (more powerful designs might well'detect a small effect) nor would it be proper to conclude that targets are the only adequate primes. What can be concluded is that nonlexical factors are almost certainly involved in the standard repetition effect. Experiment 5 The masked repetition effects observed in Experiment 1 and in Phase 1 of Experiment 4 were obtained when the prime and target were immediately adjacent. Obviously, if this effect really reflects a temporary increase in the accessibility of a lexical entry, then the same result should be obtained when other items are interpolated between the prime and target. If a masked repetition effect occurs under these conditions, then several alternative explanations of the effect can be eliminated. One such possibility is that the effects are really due to some kind of differential masking effect. For example, it could be that the visual similarity of the lowercase and uppercase versions of the same letter is greater than the average similarity of the lowercase and uppercase versions of different letters. Hence, "repeated" items are really successive presentations of visually similar forms. Because the prime presumably produces a forward masking effect on the target, it is possible that this masking effect is less for repeated items due to greater visual similarity. However, if the prime is no longer adjacent to the target and if the target is always preceded by a constant stimulus, then any such effects should be eliminated. A similar argument applies to the possibility of graphemic priming effects, because these would not be expected to persist across intervening items. It should be noted that evidence has already been produced against both of these proposals. If suich effects occurred, then nonwords should have shown the same repetition effects as did words in

691

REPETITION PRIMING Experiment 1, and graphemically similar primes should have produced facilitative effects in Experiment 2. For these reasons, it was decided to attempt to replicate the findings of Experiment 1 using nonadjacent primes and targets. Quite apart from the arguments just presented, it would also be desirable to replicate the independence of masked repetition effects and frequency. , Target items in this experiment were preceded by five context items, with the prime located in Positions 2, 3, or 4. A further manipulation involved the duration of the prime; This was presented either for 60 ms (as in Experiment 1) or for the same duration as the other context items (500 ms). These latter primes are, of course, perfectly visible and correspond to the unmasked primes used in Experiment 4. It will be recalled that these primes did not produce a clear repetition effect. The present experiment examines whether the same result occurs with a much reduced lag. Method Materials and design. A total of 192 target items was selected; half were words, and half were legal nonwords. The words were either drawn from a high-frequency range (65-90 occurrences per million) or a low-frequency range (below 5 occurrences per million). A context of 5 items was constructed for each target, consisting of 4 words and 1 legal nonword. For all targets, either the 2nd, 3rd, or 4th context item was the prime. In repeated trials/the prime was the same as the target but was in a different case. For nonrepeated trials, the prime was a completely different item. For repeated nonword trials, only 1 nonword was included in the context (the prime), and this occurred equally often in Positions 2-4. thus, every context contained t nonword, thereby preventing the presence of a nonword from signalling to the subject that the target item would be a nonword. Context items were presented in lowercase letters, and target items were presented in uppercase letters. The lengths of the context items were always matched to the length of the target. For repeated trials, half were designated as masked repetitions, and half were designated as unmasked repetitions. Two sets of materials were constructed, so that materials were counterbalanced across the Repetition factor, Thus, a repeated item in one.set was preceded by the same context in the second set except for the repetition. For example, if the first set contained the following repeated word item: contact-kitehen-chomple-trivial-dentist-KiTeHEN, the second, set contained the corresponding nonrepeated word item: contact-develop-chomple-trivial-dentist-KiTCHEN,

Tables Experiment 5: Mean Lexical Decision Times (KT in Milliseconds) and Percentage of Errors for Items Preceded by Identical or Different Primes Using Both Masked and Unmasked (no mask) Primes Masked prime Item type High-frequency words Repeated Nonrepeated Repetition effect Low-frequency words Repeated Nonrepeated Repetition effect Nonwords • Repeated . Nonrepeated Repetition effect

Unmasked prime

RT

error

RT

error

475 488 13

3.5 4.2 0.7

459 477 18

1.9 3.8 1.9

500 513 13

9.6 13.8

484 519 35

550 538 -12

4.2 9.8 6.1 -3.7

548 549 1

4.5 11.2

6.7 7.9 6.7 -1.2

random to these conditions. In each set, there were eight word conditions (Frequency X Masking X Repetition), with 12 items in each condition. For nonwords, there were four conditions (Masking X Repetition), with 24 items in each condition. Procedure. The sequence of five context items was presented at a rate of 500 ms per item except for the masked prime, which was presented for only 60 ms, Unmasked primes were presented for 500 ms, as was the target. The only departure from the general conditions of Experiment 1 was that a 500-ms warning signal was introduced immediately prior to the target, in order to reduce uncertainty about which item was the target. Subjects were instructed to read passively the context items, and to classify the uppercase item following the warning signal (a pair of separated angled brackets) as a word or nonword. ' Subjects. A total of 26 volunteer undergraduates served as subjects and were-paid for their participation in the experiment. Subjects were assigned to the two different sets of materials in the order of their appearance at the laboratory. Results

The mean lexical decision times and error rates for each condition are shown in Table 5. The results for words were analyzed separately for the masked and unmasked prime conditions and were collapsed over the position of the prime. For the masked priming condition, there was a significant main effect However, materials were not counterbalanced acro'ss of frequency, Fmin(l, 65) « 9.72, p < ;01, and the Masked-Unmasked factor; items were assigned at also a significant main effect of repetition,

692

KENNETH I. FORSTER AND CHRIS DAVIS

F'min(l, 54) = 4.39, p < .05. Because exactly the same repetition effect (13 ms) was observed for both high- and low-frequency words, there was, of course, no interaction between these main effects. The analysis of errors showed the usual effect of frequency; low-frequency words produced more errors, •F'minO, 63) = 10.06, p < .01. However, no other effects were significant or even approached significance. For the unmasked condition, there was again a significant main effect of frequency on lexical decision times, Fmin(l, 64) = 10.22, p < .01. There was also a significant repetition effect, .FminO, 66) = 13.93, p < .001. In this case, the repetition effect for low-frequency words (35 ms) was nearly twice as large as the effect for high-frequency words (18 ms), although this interaction effect failed to reach significance, F'mia(l, 59) = 2.11, p> .05. Significance was reached for the item analysis, F(\, 44) = 4.56, p < .05, but not for the subject analysis, F(\, 24) = 3.92, p > .05. Analysis of the errors showed significant effects for frequency and repetition, but no significant interaction. Several features should be noted. Although the repetition effect with masked primes (13 ms) is once again insensitive to frequency, it is much smaller than the effect observed in Experiment 1 (43 ms), the first pilot study (35 ms), and the effect observed in Phase 1 of Experiment 4 (52 ms). It could be that the increase in the interval between the prime and the target from 60 ms in the earlier experiments to a range of 1,060-2,060 ms in the present experiment is responsible. If so, then it suggests that the duration of the masked repetition effect is very limited. The results for nonwords are shown in Table 5. In the masked condition, there is clearly no repetition effect, whereas in the unmasked case, there is a reverse effect of repetition. Analysis of these results in a 2 X 2 X 2 factorial design, with Groups, Masking, and Repetition as factors, showed no significant main effects (F'min < 1). The Masking X Repetition interaction effect also was nonsignificant, Fmin(l, 58) = 2.12, p > .05, although the item analysis did show a significant effect, F(\, 92) - 5.40, p < .05. The failure of the subject analysis suggests that the interference effect observed for unmasked primes was

only observed for some subjects. A similar pattern of results was obtained for the errors, although none of the effects approached significance. Discussion The results of this experiment provide a clear replication of the results of Experiment 1. Masked primes again produce equal repetition effects (though small) for high- and low-frequency words. Because these effects were obtained when the prime and the target were separated by at least one intervening item, a graphemic priming interpretation is made less plausible. In addition, we can rule out visual interference effects because the material immediately prior to the target is held constant. The second result of interest is the fact that the unmasked primes do not show a significant frequency attenuation effect, although there is an obvious tendency in this direction. Although it would obviously be unwise to conclude that there is no attenuation at all, it does seem clear that the reliability of the frequency attenuation effect is affected by removing the requirement to respond to the prime. This is consistent with the argument that frequency attenuation is primarily an episodic phenomenon and that episodic effects are enhanced by requiring a response to tne prime. Clearly, more evidence is required to determine whether context items are capable of producing a standard, longterm, frequency-sensitive effect, but this goes beyond the scope of the present article. Finally, it should be noted that this experiment raises the possibility that lag effects can be demonstrated when subjects do not respond specifically to the prime. The unmasked primes in this experiment produced a highly significant repetition effect, whereas in Experiment 4, they did not. The most obvious explanation is that the present experiment involved a much shorter lag (an average of 2 intervening words) than did Experiment 4 (an average of 90 intervening items). If this proves to be the correct explanation, then we have further evidence that the nature of the repetition effect changes when subjects do not respond -specifically to the prime, because the standard repetition

693

REPETITION PRIMING

effect is insensitive to lag (e.g., Feustal et al., 1983; Jacoby & Dallas* 1981; Scarborough et al., 1977, 1979). Similar arguments apply to the masked repetition effect, which we have already suggested may be a very short-lived phenomenon. The next experiment attempts to establish this point more precisely. Experiment 6 When the masked prime occurs immediately prior to the target, a much larger repetition effect is observed compared with the conditions of Experiment 5, where as many as 3 words intervened. This suggests the possibility that the masked repetition effect is short-lived and that if sufficient items'intervened, no repetition effect would be observed. The present experiment was designed to test this hypothesis. Two lag values were used. In the first condition, 17 items were interpolated between the prime and the target, and in the second, only 1 item intervened. Method Items were constructed in the same way as in Experiment 5 except that the length of the context was increased to 19 words. The prime was located either in the second position (a lag of 17 items), or in the second-to-last position (a lag of 1 item). The duration of the prime was always 60 ms, and the duration of all other items was 500 ms. The target items consisted of 60 high-frequency words and 60 low-frequency words (drawn from the same ranges as in Experiment S), and 120 legal nonwords. As in Experiment S, a warning signal was provided 500 ms before the onset of the target. Materials were counterbalanced across the factors of Repetition and Lag. Subjects were told that it was important for them to read the context items. A total of 30 volunteer undergraduates served as subjects.

Table 6

Experiment 6: Mean Lexical Decision Times (RT in Milliseconds) and Percentage of Errors for Words Preceded by Masked Primes at a Short lag (1 Item) or a Long lag (17 Items) Item type High-frequency words Repeated (short lag) Repeated (long lag) Nonrepeated Low-frequency words Repeated (short lag) Repeated (long lag) Nonrepeated

RT

% error

445 460 458

5.7 3.3 5.0

490 501 511

14.0 11.7 15.3

At a lag of 17 items, however, the masked repetition effect of only 4 ms was not significant (F'min < 1; no significant item or subject effects were obtained). There was a significant effect of frequency, Fmin(l, 79) = 16.04, p < .001, but no Frequency X Repetition interaction (F'min < 1). These results confirm the expectation that the masked repetition effect dissipates rapidly because there is no detectable effect at a lag of 17 items (a delay of 9s). However, the effect at a lag of 1 item (17 ms) is still well below the values obtained in Experiments 1 and 4 (35-52 ms), where a lag of 0 was used. If the decay is a time-dependent process, then this suggests that most of the decay takes place within the first second. However, it is also possible that the decay is not timedependent but is the result of an interference effect produced by the intervening items. The present results do not permit a choice between these alternatives. General Discussion

Results and Discussion The results are shown in Table 6. With a short lag, a masked repetition effect of 17 ms was obtained. This was significant, F'm-m(l, 68) = 7.36, p < .01. There was a significant effect of frequency, F'min(l, 79) = 16.53, p < .001, but there was no significant Repetition X Frequency interaction (Fmin < 1; no significant effects were obtained in either the subject or item analyses). Apart from a significant effect of frequency, there were no other significant effects in the analysis of errors.

The experiments reported in this article have demonstrated that it is possible to produce repetition effects in a lexical decision task when the prime is masked and is unavailable for conscious report. This repetition effect differs from the normal effect in that it is insensitive to frequency (Experiments 1, 5, and 6) and is extremely short-lived (Experiment 6). It is not produced by some sublexical process such as letter priming, because no repetition effects were observed for nonwords, and there was no priming effect for graphemically similar words (Experiment 2). On the

694

KENNETH I. FORSTER AND CHRIS DAVIS

assumption that the main effect of masking the prime is to decrease the influence of any possible episodic trace of the prime, it can be concluded that the frequency attenuation normally produced by repetition is due to episodic influences. Increasing the duration of the prime (and hence making it visible) does not necessarily restore the frequency attenuation effect. At long lags (Experiment 4), the repetition effect itself was so weak that there was no reliable effect for either high- or low-frequency words considered separately, and hence no interaction could be expected. At very short lags (Experiment 5), a highly significant repetition effect was obtained, but there was no significant interaction with frequency, although there was an obvious trend in the expected direction., These experiments differ from the standard design in that the primes are not presented as target items but as part of the context of another irrelevant target word. Hence, it appears that frequency attenuation is more marked when the primes have been presented as target items, as was the case in Experiment 3, where a significant frequency attenuation effect was obtained under the same lag conditions as those of Experiment 4. These results can be explained by postulating that there are in fact two types of repetition effect in lexical decision tasks: a long-term effect and a short-term effect. The long-term effect requires that the prime be given special emphasis or salience (e.g., by presenting the prime as a target) and is sensitive to the frequency of the target word. The short-term effect requires no special status for the prime, is insensitive to frequency, and dissipates rapidly. We would further argue that the long-term effect is totally mediated by episodic factors, whereas the short-term effect is an automatic consequence of repeated access of the same lexical entry. This argument implies that there are no long-term lexical effects of repetition. This is necessary to explain why Oliphant (1983) obtained no repetition effect at all, even though it could be shown that the entries for the primes had been accessed. We now need to consider the possible mechanisms responsible for each of these effects. Consider first the long-term effect. Following Oliphant's (1983) suggestion that

the effect is strategic, it could be suggested that the locus of the episodic influence is at the decision stage of the lexical decision task. For example, as suggested by Jacoby and Dallas (1981), the fact that a repeated item accesses both a lexical entry and an episodic trace may increase the perceived familiarity of the word, which may in turn decrease decision time. To explain the frequency attenuation effect, we would need to postulate that the familiarity effect is enhanced for low-frequency words. There are several possible ways in which this may occur. For example, high-frequency words are already highly familiar, and hence the added familiarity of a recent encounter may have little impact. Or, it could be that the episodic traces of low-frequency words are either stronger or are accessed more rapidly. To explain why an increase in familiarity should decrease decision time, we need to show that there is some postaccess process that could be abbreviated of omitted. One possibility is the postaccess orthographic check (e.g., Forster, 1976), in which a candidate entry is finally checked to confirm that it is the correct entry. This process could be dispensed with altogether for repeated items, because it is highly unlikely that the candidate entry is incorrect but also happens to be the entry for a word previously presented in the experiment. This strategy may well depend on the subject's awareness that items are being repeated. Furthermore, the savings may be greater for low-frequency words, because the entries for these words ;take longer to access, and hence it is more;likely that the episodic trace will have been found in time to have any effect. Lexical access may be so rapid for high-frequency words that the postaccess check is well under way before the episodic trace is found. An alternative proposal is that the episodic trace modifies the access process itself, although the precise nature of such an effect is obscure. Within the framework of lexical search models, access time is controlled by position within the search set,:and it is therefore difficult to see how the mere existence of an episodic trace could influence access time without modifying the ordering of entries within the lexicon (the latter being ruled out on the assumption that there are no longterm lexical effects of repetition). Without

REPETITION PRIMING

any strong evidence that the effect occurs during access, the decision interpretation just offered seems preferable. If episodic retrieval is markedly contextsensitive, as suggested by the encoding specificity principle (Tulving & Thomson, 1973), then any change in the way in which the prime and the target are presented may reduce the accessibility of the trace of the prime, and hence may reduce the repetition effect. Carroll and Kirsner. (1982) reported stronger repetition effects when related words were presented in the same pairings on both occasions, which may be interpreted as an instance of such an effect. This notion might also explain why the repetition effect was so weak when the prime was presented as a context item (Experiment 4). When the target is presented, the episodic search may first scan the traces of previous target items. Only subsequently will the traces of other words be examined. This may mean that the episodic trace of the prime is not contacted rapidly enough to produce a reliable repetition effect. It is perhaps worth noting that most subjects appeared to be aware of the repetition in this experiment, so it could not be claimed that the episodic trace of the prime was not accessed; it must be that it was accessed less efficiently. If we are correct in claiming that longterm repetition effects are purely episodic, then much of the debate about the modalityspecific nature of the repetition effect loses its significance (e,g., Morton, 1979, 1980; Scarborough etal., 1979). Given the .contextual sensitivity of episodic memory, it is no longer surprising that presenting the prime and the target in different modalities should reduce the repetition effect. So, for example, the fact that picture naming does not facilitate subsequent word naming (Scarborough et al., 1979) may indicate only that episodic retrieval of the picture names was relatively slow when the same words were presented visually, A similar argument would apply to contrasts between auditory and visual presentations. The critical assumption is that episodic retrieval uses features of the test stimulus situation to direct its search, so that it first scans episodic traces that are contextually linked to the current test situation. We now turn to a consideration of the mechanism -underlying the short-term effect.

695

From the standpoint of a search model of lexical access, one may be tempted to postulate that the entries for recently encountered words are "promoted" to a higher position in the search path. However, as noted by Forbach et al. (1974), this would seem to indicate stronger effects for low-frequency words because high-frequency words may already be at the top or near the top of the search set. Because the short-term effect is insensitive to frequency, this proposal appears to be ruled out, as will all other explanations that interpret the effect in terms of the access process. That is, the constancy of the frequency effect must indicate that the access process is unmodified, and hence the shortterm effect must also be interpreted as some kind of postaccess effect. One possibility that meets this constraint is to suggest that immediately after an entry has been accessed, it is left in a moderately excited state so that information can be extracted from it more rapidly. This readout effect may be an accidental by-product of some neurophysiological process or it may serve some function, such as decreasing the time required for other processing systems (such as the parser) to extract information from the entry. The concepts of opening and closing a file entry are apt analogies from computer parlance. The task of the lexical processor is to locate the lexical entry appropriate to the stimulus, and to open the entry. When the contents of the entry are no longer required, the entry is then closed. While an entry is in the open condition, any subsequent access of the same entry will be faster because the entry need not be opened. Because this effect does not involve any reordering of entries and only operates after access has occurred, it should be independent of frequency. Moreover, such an effect would be expected to be extremely short-lived, because processes such as parsing and semantic interpretation are rapid, and hence there would be no requirement to maintain the entry in the open state beyond a period of 1-2 s. For the logogen model (Morton, 1980), there is no particular difficulty in adapting the account of long-term effects to cover the short-term effect. Originally, it was assumed that discharge of a logogen leads to a temporary lowering of threshold proportional in size to the original threshold level. Because

696

KENNETH I, FORSTER AND CHRIS DAVIS

low-frequency words have logogens with correspondingly high thresholds, it follows that larger repetition effects should occur for lowfrequency words. This account can be adapted to cover the short-term effect provided we assume that logogen discharge can occur without the subject becoming aware of the stimulus and provided we now assume that all thresholds are reduced by the same amount. However, it seems unlikely that both the original account of the long-term effect (suitably modified to incorporate episodic influences) and this new account of the shortterm effect could coexist unless some convincing account is offered for proportional threshold reduction in the case of the longterm effect but constant reduction for the short-term effect. As mentioned earlier, any episodic interpretation of the long-term repetition effect must explain why some variables that affect the strength of the episodic trace do not affect the strength of the repetition effect (e.g., Jacoby & Dallas, 1981; Jacoby & Witherspoon, 1982; Scarborough et al., 1977). Part of the explanation may be a question of timing. Episodic traces must be available quickly enough to influence lexical decisions, but this property may be irrelevant in an old-new classification task. Part of the explanation may be a question of sensitivity. For example, trace strength may be critical in discriminating whether an item has occurred during the experiment or on some prior occasion, but for the lexical decision task, any trace strength above some minimal value may be sufficient to produce an effect. Hence, the evidence suggesting that the long-term effect is not episodic may only indicate that trace strength has different effects in different tasks. It should be noted that the evidence is not all negative, because there are some parallel effects for episodic and perceptual tasks (Jacoby, 1983). In addition, the evidence from Experiments 4 and 5 suggests a further parallel, namely that lag effects may occur when context primes are used. Of particular interest is the finding that Korsakoff patients show repetition effects despite their apparent inability to recall any details of the initial presentation (Berger, 1980; Jacoby & Withenipoon, 1982). On the face of it, this fact appears to be a striking

refutation of the claim that repetition effects are episodic in nature. But it may be the case that this result shows something about the accessibility to consciousness of episodic traces in Korsakoff patients. Episodic traces can be utilized effectively in carrying out certain kinds of tasks (e.g., lexical decision) but not others (e.g., recall). Finally, there are a number of problems associated with the use of masked primes that should be considered. There have been a number of recent studies that have shown that masked primes are capable of producing semantic priming effects (e.g., Balota, 1983; Humphreys, 1981; Marcel, 1980; Marcel & Patterson, 1978; McCauley, Parmelee, Sperber,'& Carr, 1980). Much of the controversy surrounding these studies centers on the problem pf deciding whether subjects were really unaware of the priming stimulus (e.g., Merikle, 1982). Thus, it might be suggested that in the present series of experiments, the masking effect was not complete and that subjects in fact could have detected the primes, especially after practice. This point is actually irrelevant to the argument, because all that is necessary is to argue that the mask radically reduces the accessibility of the episodic trace of the prime. However, leaving this aside, it should be noted that in the pilot studies (Experiment 1) where subjects attempted to guess the properties of the prime, the same opportunities for improvement as a function of practice were available, yet no evidence of any ability to detect anything more than the most superficial aspects of the prime was obtained. It will be noted that the duration of the prime in the present experiments (60 ms) is rather longer than in previous studies (less than 20 ms). This is most likely due to the fact that a combination of forward and backward masking was: used here. It should be stressed that the masking effects are in part a function of the duration of the material presented before and after the prime (500 ms). If these words are\ also displayed for 60 ms, then the prime becomes much more visible. But the important point to note is that the impact of the evidence reported here does not depend on the claim that subjects were totally unaware of the prime. Even if it could be shbwn that they were partially aware (or

REPETITION PRIMING

even totally aware) of the prime, it would still be necessary to explain why the frequency attenuation effect is absent under these conditions. It is possible that masking is actually irrelevant to the argument. It may turn out that subsequent experiments show that context items in general fail to produce frequency attenuation effects, whether masked or unmasked. The results of Experiment 5 are not decisive on this point: Although the repetition effect for low-frequency words was almost twice as large as the effect for high-frequency words, this difference was not reliable (it is perhaps worth adding that precisely the same result was obtained in an earlier experiment that is omitted for space reasons here). However, it should be stressed that even this is a peripheral issue, because the argument concerning diminished accessibility of episodic traces could be applied equally well to this case. Clearly, a complete theory of the repetition effect will require resolution of these issues and many others. But this should not deflect attention from the central point of the present argument, which is that the repetition effect should not automatically be taken as a purely lexical effect, and in particular, that the frequency attenuation effect produced by repetition does not undermine the notion of a frequency-ordered search process. References Balota, D. A. (1983). Automatic semantic activation and episodic memory encoding. Journal of Verbal Learning and Verbal Behavior, 22, 88-104. Becker, C. A. (1979). Semantic contexts and word frequency effects in visual word recognition. Journal of Experimental Psychology: Human Perception and Performance, 5, 252-259. Berger, J. (1980). Determinants of verbal and non-verbal recognition performance in Korsakoff syndrome. Unpublished honor's thesis, Monash University, Victoria, Australia. Besner, D., & Swan, M. (1982). Models of lexical access in visual word recognition. Quarterly Journal of Experimental Psychology, 34, 313-325. Carroll, M., & Kirsner, K. (1982). Context and repetition effects in lexical decision and recognition memory. Journal of Verbal Learning and Verbal Behavior, 21, 55-69. Clark, H. H. (1973). The language-as-ftxed-effect fallacy: A critique of language statistics in psychological research. Journal of Verbal Learning and Verbal Behavior, 12, 335-359.

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Morton, J. (1979). Facilitation in word recognition: experiments causing change in the logogen model. In P. A. Kolers, M. E. Wrolstad, & M. Bouma (Eds.), Processing of visible language (pp. 259-268). New York: Plenum Press. Morton, J. (1980). The logogen model and orthographic structure. In U. Frith (Ed.), Cognitive processes in

tition effects across task and modality. Memory & Cognition, 7, 3-12. Shulman, H. G., Hornak, R., & Sanders, E. (1978). The effect of graphemic, phonetic, and semantic relationships on access to lexical structures. Memory & Cognttion, 6, 115-123. stanners, R. F., & Forbach, G. B> (1973). Analysis of

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