LANGUAGE AND COGNITIVE PROCESSES, 2002, 17 (1), 31–59
On the nature of phonological assembly: Evidence from backward masking Conrad Perry Macquarie Centre for Cognitive Science (MACCS), Macquarie University, Sydney, Australia
Johannes C. Ziegler CNRS, Aix-en-Provence, France, and MACCS, Macquarie University, Sydney, Australia The present study used the backward masking paradigm to investigate the nature and time course of phonological assembly. Two experiments were performed that tried to specify the extent to which phonological assembly is a serial process, or a process that gives special weight to consonants over vowels. Experiment 1 showed that recognition rates in a backward masking task varied as a function of the serial position of the phonemes that were shared between backward masks and target words. When the backward masks and target words shared nal phonemes, recognition rates were higher than when they shared initial phonemes. In addition, the data exhibited a weak difference between consonant and vowel preserving masks. In Experiment 2, nonwords were added to the target words of Experiment 1 to discourage guessing from the backward masks. Although serial effects of phonological assembly were again found, the consonant/vowel differences from the previous experiment disappeared. Overall, the results of both experiments showed strong serial effects of assembled phonology compared to much weaker consonant/vowel effects. Furthermore, the emergence of consonant/vowel effects appeared to be modulated by guessing strategies and the consonant/vowel structure of the words. These guessing strategies appear to be an inherent problem with the backward masking task.
Most models of word recognition and naming agree that skilled readers have the ability to compute phonological information from print without the use of lexical or semantic information; i.e., they are able to assemble Requests for reprints should be addressed to Conrad Perry, Macquarie Centre for Cognitive Science, Department of Psychology, Macquarie University, New South Wales, Australia. Email: [email protected]
This research was supported by an ARC special centre grant awarded to Max Coltheart. c 2002 Psychology Press Ltd ®
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phonology nonlexically (e.g., Baron & Strawson, 1976; Behrmann & Bub, 1992; Coltheart, 1978; Coltheart, Curtis, Atkins, & Haller, 1993; Jacobs, Rey, Ziegler, & Grainger, 1998; Paap & Noel, 1991; Plaut, McClelland, Seidenberg, & Patterson, 1996; Seidenberg & McClelland, 1989; Van Orden, Pennington, & Stone, 1990). How exactly the assembly of phonology happens is one of the most controversial issues. One of the models, the two-cycles model (Berent & Perfetti, 1995), suggests that assembled phonology occurs as a two cycle process. In the rst cycle, consonants are assembled; in the second, vowels are assembled. Support for this hypothesis came predominately from the results of a number of backward masking experiments. However, recent data using a different paradigm, the primed lexical decision task, challenge the generality of the two-cycles hypothesis (Lukatela & Turvey, 2000). In those experiments, no evidence at all was found for temporal processing differences between consonants and vowels, despite evidence for the automatic processing of phonology being found. Because the backward masking paradigm seems to produce a different pattern of performance than the more commonly used masked priming paradigm, the aim of the present study was to examine in detail the specics of the backward masking task and the logic used to interpret results. In the backward masking paradigm, rst a character mask (typically #s) appears. A target word is then presented rapidly and is immediately followed by a nonword mask (a backward mask). Finally, the same character mask is again presented over the backward mask. Participants are asked to identify the target word. The accuracy at which participants identify target words succeeded by different types of mask is then examined. This accuracy has been shown to differ, depending on the type of backward mask used (e.g., Perfetti & Bell, 1991; Perfetti, Bell, & Delaney, 1988). In Berent and Perfetti’s (1995) rst experiment, where a backward masking task was used, participants were presented with target words and backward masks at four different exposure durations (two exposure durations in a short and two in a long condition). In the short exposure condition, words that were succeeded by masks which kept the phonemically same vowels but not consonants (vowel preserving masks) were identied less accurately than words succeeded by masks which kept the phonemically same consonants but not vowels (consonant preserving masks). In the long exposure condition, consonant and vowel preserving masks had a similar effect on recognition accuracy. Berent and Perfetti suggested that because vowel preserving masks provided less benet than consonant preserving masks at an early stage of word recognition (i.e., in the short exposure condition), it implied that more consonant information had initially been activated from the target word. This effect was
particularly strong when masks and target words were presented for 30 ms each. At this short exposure duration, homophonic masks (which shared both vowels and consonants with the target word) and consonant preserving masks produced similar recognition accuracy (i.e., a ROZE is a REEZ). This nding was taken to suggest that both types of masks reinstated the same type of information (i.e., consonant information). Thus, according to Berent and Perfetti, only consonant information was assembled at short exposure durations, even if target words were succeeded by homophonic masks that shared vowel information. Because Perfetti and colleagues (Berent & Perfetti, 1995; Perfetti & Bell, 1991; Perfetti et al., 1988) never found any interaction of the masks with either the frequency or consistency of the target words, they argued that at the durations they used, the backward masking paradigm was tapping into the pre-lexical automatic assembly of phonology. It is possible to summarise the logic which Berent and Perfetti (1995) used to understand the results of their backward masking experiments. At short exposure durations, more consonant than vowel information is initially assembled from the target word. This may be because the amount of spelling-to-sound regularity in consonants is typically higher than that of vowels, making consonants easier and faster to be assembled. When a consonant preserving mask is used, it has the effect of reinstating information that has previously been partially activated from the target word. This reinstatement increases the activation of the consonants to a level where they can help word recognition performance. In contrast, when a vowel preserving mask is used at short exposure durations, the vowels that the target word shares with the mask are not necessarily reinstated. This is because vowels are not necessarily assembled from the target word at short durations, and hence are not able to benet from being reinstated. Consequently, at short durations, word recognition does not benet as much when masks and targets have vowels in common than when they have consonants in common. At longer exposure durations, vowel information is assembled from the target word. Therefore, vowels can benet from being reinstated when succeeded by vowel preserving masks. As a consequence, target words succeeded by both consonant and vowel preserving masks obtained similar levels of accuracy. So why might Berent and Perfetti’s results have produced a different pattern compared to those of Lukatela and Turvey (2000) who used the masked priming paradigm? One possibility is that the manipulation of consonant/vowel overlap in monosyllabic words is likely to be confounded with serial position as vowels are typically in the middle of a word whereas consonants are either at the beginning or at the end. There already exists much evidence that serial position is important. In a reading aloud task, for instance, Coltheart and Rastle (1994) found that the reading aloud
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latencies of irregular words were slower when the irregular phonemegrapheme correspondence occurred early in the word (see also Cortese, 1998; Rastle & Coltheart, 1999). According to Coltheart and Rastle (1994), such an effect indicates that phonology is assembled from left-to-right. Since Berent and Perfetti did not control for serial position in their study, it may be a confounding factor in their study. This possibility was examined in Experiment 1. Apart from serial position confounds, there also exist potential problems with the backward masking task, the main concern being that participants may guess from the mask. That is, since participants typically know that they must produce a word, they may use information from the mask to produce the answer. This information may not necessarily reect the automatic generation of phonology, but rather guessing strategies. If such guessing has an effect on performance, then it may explain why the backward masking results are different from the masked priming results, for which guessing is not an issue. The possibility that guessing occurs in the backward masking task was documented by Brysbaert and Praet (1992). In their experiments, they noted that under certain conditions, participants would often report the mask instead of the target word. They suggested that this meant that guessing from the backward mask occurs under certain conditions. This possibility was examined in Experiment 2.
EXPERIMENT 1 Since only a few studies have investigated the nature of the assembly process and since none of them has attempted to tease apart serial effects from consonant-vowel effects, that was the main aim of this experiment. Whether assembly proceeds from left to right or whether assembly is a function of processing differences between vowels and consonants independent of serial position can be tested in a straightforward way by comparing four letter and four phoneme Consonant-Consonant-Vowel Consonant (CCVC) with Consonant-Vowel-Consonant-Consonan t (CVCC) words. The basic idea is illustrated in Table 1. To test for serial effects, it is sufcient to manipulate the overlap between masks (which are always nonwords) and target words in a left-toright manner. That is, in one condition, masks and targets share all phonemes but the second phoneme (a 2nd position mask), in another condition masks and targets share all phonemes but the third phoneme (a 3rd position mask), and in the last condition masks and targets share all phonemes but the fourth phoneme (a 4th position mask). Note that we do not use a rst position mask to stay consistent with the design of Berent
TABLE 1 Basic planned comparisons of Experiment 1 Word Type Target Masks
crab C#AB CR#B CRA#
colt C#LT CO#T COL#
Position comparison (2nd versus 3rd versus 4th)
Consonant/vowel comparison 1 (2nd position mask has a different number of consonants than 3rd position mask)
C#AB vs. CR#B
Consonant/vowel comparison 2 (2nd and 4th position masks have a different number of consonants on CVCC words) Consonant/vowel comparison 3 (3rd and 4th position masks have a different number of consonants on CCVC words)
Note: #s indicate replaced phonemes.
and Perfetti (1995). Thus, except for the control masks, all of the masks share the same initial phoneme. The manipulation is illustrated in Table 1 (the non-overlapping phoneme is indicated with a #). The serial account would predict that word recognition performance should be different for masks which share phonemes at different positions. More specically, performance should be best when targets and masks have all three initial phonemes in common (crab-CRA#) and worst when they have the nal phonemes in common (crab-C#AB). To test for consonant/vowel effects while controlling for serial position effects, one can compare CCVC words with CVCC words (the three comparisons described below can be seen in Table 1). For example, if a 2nd position mask is used for both types of words (i.e., C#VC against C#CC), the CCVC words share vowels and consonants with the mask while the CVCC words only share consonants. Similarly, if a 3rd position mask is used (i.e., CC#C against CV#C), CCVC words only share consonants with the mask while CVCC words share consonants and vowels. Thus, if the amount of consonant/vowel overlap matters over and above serial position, we should obtain a cross-over interaction for CCVC and CVCC words for which the second and third phoneme is changed. Two weaker comparisons can be made between the 2nd and 4th position masks and the 3rd and 4th position masks. In this case, one of the mask types has a stable number of consonants that are the same as the target word in one of the word structure groups, whereas there is a difference of one consonant in the
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other. In particular, in the 2nd and 4th position mask comparison, the number of consonants shared with the target remains the same on the CCVC words (C#VC, CCV#), whereas the number of consonants is different on the CVCC words (C#CC, CVC#). In the 3rd and 4th position mask comparison, the number of shared consonants on CVCC words is stable (CV#C, CVC#), whereas the number of shared consonants on CCVC words differs (CC#C, CCV#). In sum, the goal of the present experiment is to investigate whether phonological assembly is constrained by serial and/or consonant vowel effects. Previous studies only looked at these effects in isolation. However, it is important to note that the idea of the comparisons is not to examine whether serial or consonant/vowel differences exist separately, but to examine both effects together. This is important because a consonant/ vowel effect could emerge within a serial assembly processing mechanism, if vowels were slower to process than consonants and if serial position was not controlled. Similarly, a serial position effect could emerge as a function of consonant/vowel differences, if consonant/vowel differences were not controlled (Cortese, 1998; Zorzi, 2000). The consonant/vowel and positional predictions illustrated in Table 1 were tested in a backward masking paradigm similar to the one used by Berent and Perfetti (1995). Two exposure conditions were used: A short mask exposure condition where the different position and consonant/vowel masks should have no differential effect on target recognition rates (baseline condition) and a longer mask exposure condition where differences between the different position and consonant/vowel masks should occur. The idea of the short mask exposure condition was to nd a baseline condition where the critical position masks affected the results compared to the control condition, but where no signicant differences between the position masks themselves nor interactions between the effects of mask type and word structure are found. We assume here that the absence of position effects in the presence of an advantage of position masks over the unrelated control condition suggests that only orthographic effects have occurred. Of course, such an argument requires that the critical position or consonant vowel effects are found at a longer duration, thus ruling out the possibility that phonology had already been completely assembled at the short duration (i.e., a ceiling effect). The idea of the long mask exposure group was to extend the backward mask duration such that the amount of phonology that could be assembled from the masks was greater than in the short exposure condition. In this case, if the duration is long enough, and the entire phonology of a word is not assembled at exactly the same time, then it would be expected that the effect of assembled phonology from the mask should interact with the different mask groups.
There are three possible outcomes of the experiment. First, if a serial effect is found but not a consonant/vowel effect, it suggests that phonology is assembled serially. Alternatively, if a consonant/vowel effect is found but not a serial effect, it suggests temporal processing differences between consonants and vowels exist. Finally, if both effects are found, it suggests that differences in the assembly of consonants and vowels exist, but they occur within serial constraints. Note that if no effects of mask type or interactions are found, then it suggests that the mask duration was either tapping into a stage where phonology is completely assembled or not assembled at all.
Methods Participants. Sixty-four rst year psychology students at Macquarie University participated in the experiment in order to full a course requirement. Half participated in the short exposure condition and half participated in the longer exposure condition. None knew the specic purpose of the experiments and none were told until the experiment had been completed. All had normal or corrected-to-normal vision and spoke English as their native language. Stimuli. The critical stimulus set consisted of 40 monosyllabic words. Each word had four phonemes. Two groups of 20 stimuli each were obtained by a manipulation of word structure (CCVC vs. CVCC). The two groups were matched as closely as possible on number of orthographic neighbors, consistency, and Celex frequency. Similarly, all words and masks were only four letters long. This means that the words were matched for functional units and word length. All words were also regular according to Standard Australian English. A summary of these statistics appears in Table 2. The individual items are listed in Appendix A. Four types of mask were paired with each target word. Three of the mask types differed in one single phoneme from the target word in one of the last three phonemic positions (2nd, 3rd, and 4th). The fourth mask type was an unrelated mask that had the same word structure, but shared no phonemes with the target word. For example, the CCVC word crab was masked by C#AB, CR#B, CRA# and SLEG, where #s indicate replaced phonemes. The CVCC word colt was masked by C#LT, CO#T, COL#, and FASK. Summary statistics for the masks appear in Table 2. All target words and their respective masks are listed in Appendix A. Procedure. Participants were instructed orally by the experimenter and by computer displayed text. They were explicitly told the sequence of events related to stimulus presentation and that the target word was always
PERRY AND ZIEGLER TABLE 2 Summary statistics of words and masks used
Word CCVC CVCC Mask CCVC Position 2 (C#AB) Position 3 (CR#B) Position 4 (CRA#) Control (GRUT) CVCC Position 2 (C#LT) Position 3 (CO#T) Position 4 (COL#) Control (FASP)
Mean consistency ratio
Mean number of neighbours
Mean CELEX frequency
6.6 5.8 7.1 4.7 7.05 7.15 6.15 5.3
Note: #s indicate replaced phonemes.
a real word. They were also asked to write down an answer even if they were not 100% sure what the target word was. The nature of the backward masks was not revealed to the participants until after the completion of the experiment. The experiment was controlled by an IBM compatible computer. Stimuli were displayed in white on black background on an NEC VGA monitor. Viewing distance was 60 cm. The room was well-lit by articial light. Each trial was controlled by the participant who pressed a key on the computer to start the process. The sequence of events for each stimulus was as follows: (1) a blank interval of 500 ms occurred after the participant had initiated the process, (2) a row of #######s, centred in the middle of the screen, appeared for 500 ms, (3) the target word, with the rst letter aligned with the rst # of the previous mask, appeared for 43 ms, (4) the backward mask, with the rst letter aligned with the rst letter of the target word, appeared for 28 ms or 43 ms, (see below), (5) a row of #######s, with the rst # aligned with the rst letter of the target word, appeared for 500 ms, (6) the screen was blanked until the participant initiated the next trial. In the short exposure condition, the target word was presented for 43 ms and the mask for 28 ms (43:28). In the longer exposure condition, the target word was presented for 43 ms and the mask for 43 ms (43:43). Pilot studies indicated that the 43:43 group was equivalent to Berent and
Perfetti’s 30:30 exposure condition used in their rst experiment.1 They also correspond to the times reported by Ferrand and Grainger where effects of orthography (28 ms) and phonology (43 ms) were found (Ferrand & Grainger, 1992, 1993, 1994; Grainger & Ferrand, 1996) and the 43 and 28 ms of Verstaen, Humphreys, Olson, and d’Ydewalle (1995). A set of 12 practice words paired with three of each type of mask was initially presented to each participant. The rst six test words appeared at a gradually decreasing exposure duration which was slower than that used in the experiment. The experimental stimuli were then presented in a pseudo-random order after an information screen had informed the participant that the practice trials had nished and the experimental trials were about to begin. Each participant was randomly assigned to one of four counterbalanced experimental conditions based on the time they participated in the study. The counterbalancing was performed such that each participant only ever encountered a target word once. This meant that the individual participants were only ever exposed to one-quarter of the masks.
Results The mean percentage of times the target words were correctly identied for each of the critical conditions is presented in Figure 1. The exact values can be found in Appendix B. One item, drag, was excluded from the analysis due to an error in a mask. In terms of correct recognition, the overall data were analysed in a 4 £ 2 ANOVA that resulted from the factorial combination of mask type (2nd vs. 3rd vs. 4th vs. unrelated) and word structure (CCVC vs. CVCC). ANOVAs were computed with both participants (Fp ) and items (Fi) as random variables. A further 3 £ 2 ANOVA that resulted from the factorial combination of mask type without the control group (2nd vs. 3rd vs. 4th) and word structure (CCVC vs. CVCC) was used to examine whether there was an overall effect of serial position on recognition. Finally, three additional 2 £ 2 planned ANOVA’s were used to address the question of whether assembly proceeds serially from left to right or differently for consonants and vowels. Each of those ANOVAs compared one of the possible permutations between two of the non-control mask groups (i.e., 2nd vs. 3rd, 2nd vs. 4th, and 3rd vs. 4th). The reason for using these ANOVAs was discussed earlier (see also Table 1). The data from the false backward 1
Because the standard refresh rates of IBM PC monitors are approximately 14 ms, it is technically fairly difcult to get exactly 15 and 30 ms, without using a tachistoscope. Since Berent and Perfetti (1995) also used a PC display, those times are likely to be only categorical. We assume that a presentation time of 28 ms and 43 ms for target word and mask respectively is the closest approximation to their 15:30 condition.
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Figure 1. Recognition accuracy of CCVC and CVCC words used in Experiment 1 as a function of mask type and mask duration.
mask reportage (i.e., when the backward masks were given instead of the target words) was analysed using the same comparisons as the correct identications, excluding the 4 £ 2 ANOVA. In the false mask report analysis, the overall 4 £ 2 ANOVA was of no theoretical interest, because the main idea was to examine whether patterns of false mask reportage (guessing) would affect potential serial or consonant vowel effects. This is more appropriately assessed in the 3 £ 2 ANOVA rather than in an overall 4 £ 2 ANOVA. Short exposure condition (baseline). The overall 4 £ 2 ANOVA examining the main effect of mask type was signicant by participants and items, Fp (3, 93) ˆ 22.14, p < .001; Fi (3, 111) ˆ 12.57, p < .001. Similarly, a signicant main effect of word structure was found by participants, although it did not reach signicance by items, Fp (1, 31) ˆ 8.04, p < .01; Fi(1, 37) ˆ 2.38, p ˆ .13. Those results suggest that the positional masks affected the recognition of the target words over and above the control masks, whose recognition performance was much lower (CCVC : 29.60%; CVCC : 23.48%). The 3 £ 2 ANOVA examining the main effect of position was not signicant, both Fs < 1. There was a signicant effect of word structure by participants, however, Fp (1, 31) ˆ 6.72, p < .05; Fi (1, 37) ˆ 2.22, p ˆ ns. The three further 2 £ 2 planned ANOVA’s comparing the different mask groups showed no signicant Mask Type £ Word Structure interactions, all Fs < 1. Moreover, the only main effect to reach signicance was that of word structure, 2nd and 3rd masks: Fp (1, 31) ˆ 5.64, p < .05; Fi (1, 37) ˆ 2.58, p ˆ .12; 2nd and 4th masks: Fp (1, 31) ˆ 3.03,
p ˆ .092; Fi < 1; 3rd and 4th masks: Fp (1, 31) ˆ 4.99, p < .05; Fi (1, 37) ˆ 1.80, p ˆ .19. Finally, since false mask reportage only occurred 2.0% of the time, no analysis was performed on those data. The results of the experiment suggested that the short exposure condition (43 : 28) provided an effective baseline to which other mask durations could be compared. This is because there were no word structure by position interactions or main effects of position. Thus, although there was an effect of the mask compared to the control group, there were no effects of the critical conditions. This suggests that the effect of the mask was mainly graphemic at this short exposure duration. It is unlikely that the absence of serial or consonant/vowel effects at this duration was a ceiling effect of phonology being already fully assembled, since such effects were found in the longer exposure duration. Here we assume that orthographic recognition of short words is largely parallel, and hence does not cause serial or consonant-vowel effects. In contrast, we assume that assembled phonology may cause positional effects to occur. Interestingly, there was some tendency for CCVC words to be recognised more accurately than CVCC words. Although not relevant for the hypothesis under examination, this nding has been replicated in a number of similar perceptual identication tasks (Perry & Ziegler, 2000). In those experiments, the difference in the processing was attributed to long-term learning constraints causing CCVC words to be more quickly processed than some types of CVCC words (see Perry & Ziegler, 2000, for a further discussion). Longer exposure condition. In the overall analysis (4 Mask Type £ 2 Word Structure ANOVA), the main effect of mask type was signicant by participants and items, Fp (3, 93) ˆ 55.68, p < .001; Fi (3, 111) ˆ 20.69, p < .001. Target recognition was generally better when target words were followed by a 2nd position (C#AB) mask, intermediate when followed by a 3rd position (CR#B) mask, and worst when followed by a 4th position (CRA#) mask. The signicance of this is examined below. Target recognition was at oor when followed by an unrelated mask (e.g., crabSLEG; CCVC : 8.55% ; CVCC 6.88%). The main effect of word structure was not signicant and nor was the Mask Word £ Structure interaction, both Fs < 1. Thus, differences in the consonant and vowel structure of target words and masks did not appear to affect the results signicantly. A 3 Position £ 2 Word Structure ANOVA performed only on the mask groups that manipulated position (i.e., not the control group) showed a main effect of position that was signicant by participants and items, Fp (2, 62) ˆ 5.40, p < .01; Fi(2, 74) ˆ 3.20, p < .05. Again, the Position £ Word Structure interaction did not reach signicance, both ps ˆ ns. In terms of false mask reportage, only the main effect of word type was
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signicant, Fp (1, 31) ˆ 8.96, p < .01; Fi (1, 37) ˆ 7.84, p < .01. Since this variable is not of theoretical importance alone, we do not discuss this main effect further here. To further examine interactions between the effects of position and word structure, three 2 £ 2 ANOVAs were performed. The ANOVAs suggested that serial position affected correct recognition, with a signicant main effect between the 2nd and 4th (C#AB vs. CRA#) position masks, Fp (1, 31) ˆ 10.78, p < .005; Fi (1, 37) ˆ 5.92, p < .05; and a signicant main effect by participants between the 2nd and 3rd (C#AB vs. CR#B) position masks, Fp (1, 31) ˆ 7.35, p < .01; Fi(1, 37) = 3.41, p ˆ .073. The main effect of position was not signicant on the 3rd and 4th (CR#B vs. CRA#) position comparison, both Fs < 1. The critical mask type £ word structure interaction approached signicance by participants in the 2nd and 3rd (C#AB vs. CR#B) position comparison: Fp (1, 31) ˆ 4.09, p ˆ .052; Fi (1, 37) ˆ 1.82, p ˆ .19, and a similar, near signicant result was found in the 3rd and 4th (CR#B vs. CRA#) position comparison: Fp (1, 31) ˆ 3.23, p ˆ .082; Fi (1, 37) ˆ 1.73, p ˆ .20. No interaction was found between the 2nd and 4th (C#AB vs. CRA#) position comparison, however, both Fs < 1. As can be seen in Figure 1 and conrmed in the above analyses, interactions between word structure and mask type appeared to exist for two out of three comparisons. However, they were only marginally signicant by participants and not signicant by items. As concerns the most critical interaction, the decrease in identication accuracy between the 2nd and 3rd position masks was less for the CCVC words that used a 2nd position vowel and 3rd position consonant preserving mask (C#AB, CR#B) compared to the CVCC words that used a 2nd position consonant and 3rd position vowel preserving mask (C#LT, CO#T). Such a result could be interpreted as a positionally constrained advantage for consonant preserving masks. Similarly, the difference in accuracy rates between the 3rd and 4th (CR#B vs. CRA#) position masks also appeared to show an interaction between the CCVC and CVCC words, although it was not signicant. With respect to serial effects, the main effect of position was signicant by participants and items. Although the contrast between the most extreme mask groups (2nd and 4th position masks) was signicant by participants and items, the less extreme comparisons between the adjacent phonemes were not signicant by items. Such a pattern is similar to the one of Rastle and Coltheart (1999). In their reading aloud study, they found a signicant effect of assembled phonology on the second phoneme of words (as we did). However, on latter phoneme positions, they were not able to nd signicant effects of assembled phonology.
Discussion In the present backward masking experiment, we exploited the fact that one can tease apart potential effects of serial assembly from effects of consonant/vowel assembly by using different word types (i.e., CCVC vs. CVCC words) in combination with masks that differ from their respective target word in either the second, third, or fourth phonemic position. With respect to the issue of whether assembly proceeds from left to right in a serial manner, a main effect of phoneme position was found. When the backward mask and the target word shared nal phonemes, recognition rates were higher than when they shared initial phonemes. It should be pointed out that the direction of the serial effect was the opposite of what was predicted. If the assembly of phonology proceeded from left to right, recognition accuracy from masks that share initial phonemes with the target word (e.g., CRA#) should have been higher than those which shared latter phonemes (e.g., C#AB). In other words, because early phonemic positions of the target word would have had the greatest chance of being assembled, masks that share these positions would have had the greatest chance of reinstating them (Berent & Perfetti’s reinstatement logic). Similarly, a mismatching phoneme at the beginning would have had the greatest chance of causing inhibition. In contrast, different phonemes toward the end of a word should have had the smallest chance of being assembled and the least chance of inhibiting performance. Thus, on rst glance, the present results would suggest a right-to-left assembly process rather than a left-to-right assembly. However, this pattern can still be accounted for by a left-to-right assembly if one assumes that phonological assembly has the greatest impact on places where initial activation from the target word is weakest. Therefore, if assembly proceeds from left to right, initial phonemes from the target word would be more strongly activated than latter phonemes. Thus, reinstating the already sufciently activated initial phonemes may have a smaller effect on overall recognition performance than reinstating the more weakly activated nal phonemes. Similarly, any inhibition from different phonemes would be likely to be greater at latter positions, since people would have to rely more on the mask for correct identication due to less activation from the target word in those positions. It is important to note that the previous explanation relies on the fact that masks can have both inhibitory and facilitatory effects. The inhibitory effects can be seen from the overall results, where participants had lower accuracy rates in the longer mask condition. Facilitatory effects can be found in Berent and Perfetti (1995). Inhibitory effects clearly cannot come from a reinstatement process, since that predicts that the masks should be benecial. The most likely explanation for the inhibitory effect is that the
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incorrect letter in the mask interferes with processing of the target word. Here, the incorrect letter may cause competition with the correct one from the target word, and thus lower overall accuracies. In addition, the inhibitory effects show that the target word cannot have been processed fully before the mask appeared, otherwise no inhibitory effects would be shown. Thus the inhibitory effects further support the possibility that the timing durations were set such that phonology had been partially, but not fully, assembled. Finally, the present data do not offer strong support for the hypothesis that assembly gives a dominant role to consonants over vowels (Berent & Perfetti, 1995). When we compared CVCC and CCVC words succeeded by a 2nd position mask (e.g., C#AB and C#LT) with CVCC and CCVC words succeeded by a 3rd position mask (e.g., CR#B and CO#T), the strongest comparison for gathering evidence in support of such a model, we predicted a cross-over interaction under the assumption that consonantpreserving masks help word recognition more than vowel-preserving masks. A weak interaction was found (marginally signicant by participants and not signicant by items). However, the absolute recognition accuracy did not show a high-low versus low-high pattern for the 2nd and 3rd position masks of the CVCC and CCVC words, respectively. Rather, recognition accuracy appeared to show a decreasing trend over the two positions, with the 3rd position consonant preserving masks (CR#B) causing accuracy rates not to decrease as much as the 3rd position vowel preserving mask (CO#T). This trend can be seen from the recognition rates of the 2nd and 3rd position masks of the CCVC words. In that comparison, the 2nd position (i.e., the vowel-preserving mask) had a slightly higher recognition accuracy than the 3rd position consonant preserving mask (although a post-hoc check showed that that difference was not signicant, both ts < 1). Those accuracy rates are in the reverse direction of those predicted by a strict two-cycle model of assembly. One can also exclude the possibility that the absence of a strong consonant/ vowel effect was due to phonology not yet being assembled because, if so, we should not have found a position effect.
EXPERIMENT 2 In our previous experiment, there was a weak interaction between word structure and position in the long exposure condition. That is, masks changing the second and third phoneme of a word appeared to help recognition more (even if not signicantly) when they shared consonants with the target word compared to when they shared consonants and vowels, although these differences were positionally constrained. One
explanation of this is that consonant/vowel differences exist, but the task was simply not sensitive enough to nd strong consonant/vowel effects. Although the previous explanation is one possibility, the fact that strong serial effects were found suggests that the task was indeed sensitive enough to examine assembled phonology. Furthermore, since there were such strong effects, and since using reinstatement logic to interpret those results would have led to a right-to-left assembled phonology hypothesis, it was necessary to offer a different account of events in the backward masking task. This creates a problem for the interpretation of the weak consonant/ vowel effects that were found, because if reinstatement logic is not accepted, then there needs to be some alternative account of those effects. One alternative explanation is that the differences were not caused by reinstatement, but rather by differences in guessing from the backward mask. That is, information from different aspects of the mask (such as position or consonant and vowel status) may help recognition to a different extent, even if processed to a similar amount. It may be the case, for instance, that people guess words on the basis of various phonotactic constraints. This may be particularly so with segments from the onset clusters of CCVC words. This is because the second consonant in CC onset clusters (e.g., blob) can typically only be an /l/ or /r/ phoneme (except after /s/), whereas the other segments are less constrained. Thus some of the interactions in the rst experiment may have been caused by people’s ability to infer (guess) correct target letters on the basis of phonotactic constraints whenever they were unsure about the correct letters. In addition to these phonotactic constraints, there are also other studies that suggest people are able to guess words from consonant information more accurately than from vowel information. Miller and Freidman (1957), for example, found that people could read text in context even if the vowels were replaced with a star. One way to examine whether the results of the previous experiment were affected by guessing is to change the conditions of the task. In the previous experiments, it was likely that some sort of guessing could have occurred for two reasons. First, participants were asked to write down an answer, even if they were not completely sure of what the word was. Second, only real words were used as targets. Thus, participants may have been able to take advantage of guessing using information derived from the mask (see Brysbaert & Praet, 1992) when they were not sure of the target word. In the experiment below, a deliberate attempt was made to examine whether potential patterns of guessing were the same over the different mask groups. For this purpose, nonwords were added to the target words to reduce guessing. This allowed us to assess the potential contribution of guessing. If the pattern of guessing on the words is constant over the
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different mask positions and word types, then a similar pattern of responses as the previous experiment should occur. Alternatively, if people are more willing to guess words from consonants rather than vowels (for instance), then some of the difference between the consonant and vowel preserving mask groups should be reduced. This is because by adding the nonwords, people should not be able to use the consonant information to guess the target as reliably. Note here that although the nonwords also share similar phonotactic constraints as the words, even in the worst case where adding nonwords does not lead to an overall reduction in guessing, the nonwords should lead to less guesses on word targets being correct. Take for example the case where it would be possible to determine a word from partial information and be correct 100% of the time if only words were used, as in the rst experiment (for example, if one perceived b#ob for blob). In the rst experiment, any guesses would always lead to the correct answer, if only phonotactically correct words were accepted. However, if nonwords are added, then even with phonotactic constraints, the probability of generating a word answer is less, since nonword answers may be also given (e.g., b#ob could be blob or brob). Thus the addition of nonwords increases the number of nonword answers that are possible from partial information, and therefore reduces the impact of guessing on the word responses.
Methods Participants. Twenty-eight rst year psychology students at Macquarie University participated in the experiment in order to full a course requirement. None knew the specic purpose of the experiments and none were told until the experiment had been completed. All had normal or corrected-to-normal vision and spoke English as their native language. Stimuli. Exactly the same words and backward masks as the previous experiment were used, except that the drag mask was xed. In addition, 40 nonwords were added. For each nonword, 4 backward masks were used. These nonwords and backward masks were constructed in the same way as the words, except for the lexicality aspect. Thus there were two groups of nonwords, one with a CCVC structure and the other with a CVCC structure. Similarly, for each nonword, four different masks were constructed. Three of these masks changed either the second, third, and fourth phonemes of the word. The fourth was a control mask that changed all of the letters and phonemes. The nonwords and masks appear in Appendix A. Furthermore, an additional 12 practice trials were used before the test stimuli. Those practice stimuli were all nonwords. The
backward masks that succeeded the practice stimuli were balanced such that there were three masks from each of the four types of mask used. Procedure. The procedure was identical to the previous experiment apart from the instructions. The instructions were changed such that participants were told that the rst letter string could either be a word or a nonword, whereas the second would always be a nonword. The target words and masks were presented for 43 ms each.
Results The data were analysed in the same way as the previous experiment. The mean recognition rate of the non-control words can be seen in Figure 2a. The exact values can be found in Appendix B. Responses relating to the nonword targets are not reported since the correct responses were at oor with an average rate of only 6.7% correct. A 4 £ 2 ANOVA examining whether the masks affected people’s identication accuracy was signicant by participants and items, Fp (3, 81) ˆ 30.99, p < .001; Fi(3, 114) ˆ 23.11, p < .001. This suggests that the positional masks affected the recognition accuracy of the target words differently to the control words, which were at oor (CCVC : 6.4%; CVCC : 0.71%). There was no signicant Word Structure £ Mask Type interaction, both Fs < 1. On the more specic 3 £ 2 ANOVA examining only non-control masks, a signicant main effect of mask type was found by participants and items, Fp (2, 54) ˆ 8.09, p < .005; Fi(2, 76) ˆ 5.07, p < .01, showing that identication performance varied as a function of serial position. To further examine serial and consonant/vowel effects, the same three planned comparisons used in the previous experiment were made on the correct responses of the words. The results of the comparisons on the
Figure 2. (a) Recognition accuracy of CCVC and CVCC words used in Experiment 2 as a function of mask type; (b) incorrect mask reportage on CCVC and CVCC words used in Experiment 2 as a function of mask type; (c) recognition accuracy of CCVC and CVCC words used in Experiment 1 corrected for guessing as a function of mask type.
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correct responses were similar to those of the previous experiment. There was a signicant main effect of mask type between the 2nd and 4th position masks, Fp (1, 27) ˆ 18.04, p < .001; Fi (1, 38) ˆ 14.46, p < .001. There was also a main effect between the 2nd and 3rd position masks which was signicant by items, but not participants, Fp (1, 27) ˆ 3.61, p ˆ 0.065; Fi(1, 38) ˆ 5.87, p < .05. No main effect of position was found between the 3rd and 4th position masks, Fp (1, 27) ˆ 1.08, p ˆ ns; Fi(1, 38) ˆ 2.01, p ˆ ns. Interestingly, the word structure by mask type interactions that approached signicance in the previous experiments were no longer even close to signicance, all Fs < 1. Overall, the results do not offer strong support for a pure consonant/ vowel model of phonological assembly. On the CCVC words, for instance, the 2nd position vowel preserving masks had a higher correct recognition rate than the 3rd position consonant preserving masks (41% vs. 33%). A post-hoc check suggested that that difference was not signicant (both ps > .2). Although, the result was in the opposite direction predicted by such a model. Similarly, not a single one of the three Word Structure £ Mask Type interactions was signicant, including the strongest comparison between the 2nd and 3rd position masks. This was despite a signicant effect of position being found on the most extreme position comparison, between the 2nd and 4th position masks. This result suggests that assembly had taken place from the mask. Furthermore, the results suggest that if consonant and vowel differences exist, they are fairly small and difcult to nd once position and guessing effects are taken into account, at least at the mask intervals we used. It is possible to further understand what happened to the consonantvowel differences obtained in the rst experiment by examining the incorrect responses where the mask was given instead of the word. Unlike the previous experiment, where the pattern of backward mask reportage was similar across the different mask position groups, the pattern appeared to differ somewhat in this experiment. In addition, the extent of mask reportage was also much increased, with backward masks given as answers 26.0% of the time. Thus adding nonwords as targets also increased the amount of times nonword masks were reported as answers. A graph showing mask reportage with respect to mask type appears in Figure 2b. To examine the pattern of incorrect mask reportage, the same analysis that was done with the correct answers was performed, except that the control mask group was ignored since it was not of theoretical importance for this analysis. The results showed that the pattern of incorrect mask reportage was not the same across the different groups. A 3 £ 2 ANOVA found a main effect of mask type that was signicant by participants, Fp (2, 54) £ 3.42, p < .05; Fi (2, 76) ˆ 1.78, p ˆ .18. Participants also appeared to give CCVC nonword masks more commonly than CVCC
nonword masks, although this result was also only signicant by participants, Fp (1, 27) ˆ 8.83, p < .01; Fi (1, 38) ˆ 2.65, p ˆ .11. In terms of the three 2 £ 2 ANOVAs, a signicant effect of word structure was found in the 2nd vs. 3rd position mask comparison, Fp (1, 27) ˆ 7.10, p < .05; Fi (1, 38) ˆ 4.69, p < .05, and by participants in the 2nd vs. 4th position mask comparison, Fp (1, 27) ˆ 5.93, p < .05; Fi (1, 38) ˆ 2.91, p ˆ .096. The effect was not signicant in the 3rd vs. 4th position comparison, Fp (1, 27) ˆ 2.55, p ˆ .12; Fi < 1. Note that we will not discuss this main effect further as it is not relevant to the discussion here. More interestingly, an effect of mask type that was signicant was found in the 2nd vs. 4th position mask comparison, Fp (1, 27) ˆ 5.93, p < .05; Fi(1, 38) ˆ 4.15, p < .05. In addition, in the 3rd vs. 4th position group, the interaction between mask type and word structure was almost signicant by participants, Fp (1, 27) ˆ 4.00, p ˆ .056; Fi (1, 38) ˆ 2.82, p ˆ .14. The results of the incorrect mask reportage analysis suggested that participants gave the nonword masks as answers in a manner that was not the same across the three different mask types. If the two word structure groups are collapsed, the results appear to suggest that false mask reportage for nonwords was greater for masks that changed phonemes toward the end of the target words (2nd position 23.6%; 3rd position 27.1%; 4th position 32.9%). However, if the results of the comparisons that did not reach signicance by items are taken into consideration, then a slightly more complex picture emerges. Here, the results appear to be caused by participants giving more 4th position nonword masks than the 2nd or 3rd position groups with the CVCC words, and by participants giving fewer 2nd position masks than the 3rd or 4th position groups with the CCVC words. If the greater number of times a nonword mask is reported reects a greater number of answers that were guessed from partial mask information in the rst experiment, then it would explain the weak interactions found in the rst experiment. In this case, the pattern of results almost perfectly reects the pattern found in the rst experiment, minus the serial effect. This can be seen in Figure 2c. In that gure, the mean results of the rst experiment were taken. Then, for each word structure group in the second experiment, the difference between the group with the smallest number of nonword mask reportings and the other two mask position groups was calculated. The difference between each of these two groups was then subtracted from the means of the rst experiment. Here, the difference values generated from the second experiment were assumed to reect an estimate of the differences in guessing patterns across the three groups of Experiment 1. Thus the idea of the graph is to show the results of Experiment 1, corrected for potential differences in guessing. As can be seen, the results appear to decline in a linear manner with essentially no effect of CV status.
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To illustrate this procedure, take the following example based on CCVC masks. In that group, false mask reportage occurred 25%, 35%, and 33% of the time for the 2nd, 3rd, and 4th position masks, respectively. Thus the group with the least false mask reportage was the 2nd position group (25%). The difference between the 2nd position group and the 3rd position group is therefore 10%, and the difference between the 2nd position group and the 4th position group is therefore 8%. Subtracting the 10% from the 3rd position group of Experiment 1 gives 28% and subtracting the 8% from the 4th position group gives 22%. Note that we still believe the serial effect found in our data is in fact an underlying serial effect caused by a serial assembled phonology mechanism, rather than guessing. This is because the serial effect was stronger in Experiment 2 than Experiment 1. This was despite the fact that the conditions under which guessing would occur on words was reduced. Thus under task conditions that should discourage guessing on words, the serial effect was still found. Similarly, the pattern of guessing also supports a serial interpretation of the results. This is because incorrect mask reportage increased as correct identication decreased. Thus in early positions, where a serial account would predict the most assembly would have occurred, the least guessing occurred. In the last position, where a serial account would predict the least phonology would be assembled, and thus the most guessing should occur, the most guessing occurred. Alternatively, if the underlying results were caused by participants guessing from the mask, and if that guessing occurs at a different quantitative level for different positions, then the opposite result should have been found. Here, more guessing should have led to more correct responses (by chance). Thus accuracy rates should have been highest where the most guessing occurred. But that was not so, it was the opposite.
GENERAL DISCUSSION Detailing the nature of phonological activation in visual word recognition rather than simply showing that phonological activation exists is a necessary step in understanding reading (e.g., Frost, 1998). Such an approach requires the specication of the mechanisms by which phonology is activated (e.g., Plaut et al., 1996; Van Orden & Goldinger, 1994), the grain sizes used in this computation (e.g., Treiman, Mullennix, BijeljacBabic, & Richmond-Welty, 1995), and the time course of phonological activation (Ferrand & Grainger, 1992, 1993, 1994; Grainger & Ferrand, 1996; Perfetti & Tan, 1998). The study of Berent and Perfetti (1995) provided an important contribution in this enterprise. Unlike previous studies that had used backward masking experiments simply to examine whether one could nd
evidence for a prelexical generation of phonology (Naish, 1980; Perfetti & Bell, 1991; Perfetti et al., 1988), Berent and Perfetti used the task to examine specic properties of the generation of phonology. The results they reported suggested that phonology was assembled in two cycles, with consonants being assembled before vowels. Recently, however, Berent and Perfetti’s results have gone under some criticism. In a series of nine experiments, Lukatela and Turvey (2000) found no evidence for a consonants and then vowels assembly. This was despite the fact that they found evidence for the automatic assembly of phonology. The present study followed up on Berent and Perfetti’s approach by investigating not only the role of consonants and vowels in the assembly process but also the role of serial left-to-right assembly. This was done by comparing CVCC with CCVC words for which the overlap between a mask and a target word was manipulated in a serial manner. One major result of our study was that we found serial effects in word recognition. Masks that shared nal phonemes with the target word were generally more effective than masks that shared initial phonemes. It was concluded that, in backward masking, the mask produces the greatest benets where phonological information was the most weakly activated from the target word. Because phonology is most weakly activated towards the right given a left-to-right assembly, masks that reinstate the end of words will help word recognition to a greater extent than masks that reinstate the already well activated information at the beginning of words. Note, however, that this interpretation is in conict with Berent and Perfetti’s claim that masks reinstate those phonemes more effectively that have been initially activated to a greater extent. In contrast to this claim, our results seem to suggest that masks affected the recognition process more where less phonological information had been assembled from the target words, rather than where more phonological information had been assembled. The interpretation that masks are more effective where less information is initially assembled can also explain a particular pattern of results in Berent and Perfetti’s (1995) study that seemed somewhat hard to reconcile with the traditional reinstatement logic. In their fourth experiment, it was difcult to explain why identication accuracy of words replaced by vowel and consonant preserving masks was more similar when the target words contained complex rather than simple vowel correspondences. Here, if it is assumed that complex vowels are slower to assemble than simple vowels, the advantage of consonant over vowel preserving masks should have been greater for words with complex vowel correspondences because the initially longer processing of complex vowels should have resulted in lesser activation being generated. Because the complex vowel was initially
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activated to a smaller extent, the mask should have reinstated the vowel less efciently. However, just the opposite was found. According to our claim that the mask helps more where less phonological information has initially been activated, Berent and Perfetti’s (1995) seemingly contradictory result nds a natural explanation. That is, because the more complex vowel correspondences have less chance of being initially assembled from the target word, an identical vowel from the backward mask would have a greater chance of helping recognition. It would, therefore, be expected that vowel preserving masks containing similar complex correspondences would have a greater positive effect on recognition accuracy than vowel preserving masks containing similar simple correspondences. Consequently, the difference between consonant and vowel preserving masks would be less when the target words contained complex compared to simple vowel correspondences. A second major result of our study was the failure to nd systematic consonant/vowel differences in the assembly process. This result stands in contrast to Berent and Perfetti’s (1995) observation that consonants are activated more quickly than vowels. However, they did not control for phonemic position differences between the masks and target words. Because our study found strong effects of phoneme position, which suggest that phonology assembled from the mask had affected the results, it may well be possible that some of the consonant/vowel differences were actually due to a confound with phoneme position. Although we do not claim this is evidence against consonant/vowel processing differences, it does suggest that it would be useful to show the existence of consonant/ vowel effects once serial position has been controlled for. At present, such data do not exist, and our attempt to nd position-independent processing differences between consonants and vowels failed. Another potential problem with the data from the backward masking task is that it may not only reect reinstatement processes, but also differences in guessing from different types of mask. In our second experiment, this issue was addressed. This was done by using both nonwords and words as target stimuli, rather than just words. The results of that experiment showed that the serial effect persisted while any hint of a consonant/vowel effect disappeared. This result suggests that the consonant/vowel effects in Experiment 1 may have been amplied by guessing target words from partial information derived from the masks. It should be noted, however, that even if one assumes a serial assembled phonology process, the data we found do not rule out the possibility that consonants are quicker to assemble than vowels. Such differences may, for instance, be constrained to occur within a serial assembly process. Given that such an assembly process is likely to be fast for individual spellingsound correspondences, it means that differences between the assembly
speed of individual units are likely to be small. This consideration is particularly important in the present experiments because only regular words with simple vowels were used as stimuli. Perhaps the most important observation of the present study was that small differences in target words and backward masks can lead to large differences in recognition accuracies. In both the rst and second experiment, for instance, signicant main effects of mask type were found. Note that both word types used four phonemes and that the masks differed only in the position of the single changed phoneme. The nding that these small differences can cause such effects has implications for Berent and Perfetti’s (1995) backward masking results. The majority of their stimuli had consonant preserving masks that changed the rst vowel after the initial consonant. Similarly, the majority of the vowel preserving masks changed the rst consonant after the rst vowel. Thus, in the light of our results, it is clear that such a set of masks is likely to produce an accuracy difference in favour of the consonant preserving masks (as was found with our stimuli). However, as we showed, such a difference is not necessarily related to consonant and vowel processing differences. It could also be related to positional differences. Similarly, it could be due to differences in people’s willingness to guess what the word is, and guessing differences between masks that change different types (i.e., consonant and vowel) of information. This leads us to two general problems with the backward masking task. First, it is difcult to tell exactly why different types of masks cause different accuracy rates. That is, the different accuracy levels caused by different mask types may not be caused by automatic processing of phonology from the mask. Rather, reporting of the target words may be such that participants extract partial information from the mask to help complete parts of target words they are not sure of. Such a possibility was rst suggested by Brysbaert and Praet (1992) and was conrmed in our second experiment. In our second experiment, false mask reportage occurred on over onequarter of the total answers, compared to our rst experiment that used the same presentation speed, where false mask reportage occurred at about half that rate. Moreover, false mask reportage differed for different types of mask. That suggests that the composition of target words modulates the answers given by participants. More importantly it also suggests that participants do indeed use partial information extracted from the mask when determining what the target word should be. The most straightforward interpretation of this is that participants use information from the mask to try to complete parts of the word that they did not initially perceive. When they are unsure of certain parts, they seem to guess from whatever information they extracted (including from the mask). Such
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guessing, which can be empirically demonstrated in an experiment that uses nonwords as targets, may be hidden in tasks where only word responses are needed. In this case, participants may not give nonwords as answers, even when that is what they perceive, preferring instead to guess word answers. This can be seen from the discrepancy between target mask reportage from our two experiments. Despite the fact that exactly the same target words and masks were used, backward masks were reported as target words twice as often when nonwords were also used as target words. Unless the task conditions caused a large difference in automatic processing, which seems unlikely, the most reasonable explanation of this is that participants simply did not write down nonwords in the rst experiment when they knew that the answers were always real words. This suggests that interpreting the results from experiments using the backward masking paradigm is difcult, since any patterns in the data may simply reect such strategies, rather than the automatic processes of interest. It is further complicated by the possibility that certain masks may have different phonotactic and orthographic constraints. Thus, if guessing occurs in the task, certain combinations of letters and phonemes allow more accurate guessing than others (such as the second phoneme in a two consonant onset cluster, which is highly constrained). This is another factor that may inuence the results and that is not caused by automatic activation. A second problem with the task is that the actual logic used to interpret data allows multiple interpretations of a given set of data. This can be seen from the results reported here versus those reported by Berent and Perfetti (1995). In our study, we used the logic that the mask interferes with processing most where least phonology has been assembled from the target word. This interpretation was forced on us by the data. The alternative would have meant to hypothesise a right-to-left assembled phonology mechanism that is not only logically implausible given that reading and speech production occur from left to right but that is also inconsistent with previous empirical data (Coltheart & Rastle, 1994). However, if exactly the opposite pattern had been found, then it would have been possible to conclude that the mask reinstated the phonemes that were most active in the target word. Thus it appears that we could have found either a left-toright decline in accuracy or a right-to-left decline and still concluded that serial effects exist. Thus, at present, the extent to which backward masks cause inhibition and facilitation under different circumstances appears unclear. It therefore suggests that some caution should be used when interpreting results from the task. In conclusion, the backward masking experiments reported here provide further evidence in support of a serial assembled phonology mechanism. The results need to be taken with caution, however, as a number of
problems were observed with the backward masking paradigm. These include the possibility that the task is susceptible to guessing, the fact that extremely small differences in word and mask structure can cause large differences in identication accuracy, and theoretical problems with interpreting exactly how backward masks affect the recognition of target words. Manuscript received September 1999 Revised manuscript accepted August 2000
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APPENDIX A Stimulus materials used in Experiment 1. Each row identies, in order, target word, same last two phoneme mask, same rst and last phoneme mask, same rst two phoneme mask, and control mask. dusk gulp hilt jolt kelp lump melt musk pimp pond pump runt sold sulk tilt tusk weld wept wisp zest blob brag brim clad clog drab ap op glut grab grim plot plug pram scab snag spun stab trim twin
DOSK GILP HELT JULT KILP LEMP MULT MISK PAMP PUND PAMP RINT SULD SELK TULT TOSK WUND WUPT WESP ZAST BROB BLAG BLIM CRAD CROG DWAB FRAP FROP GRUT GLAB GLIM PROT PRUG PLAM SNAB SMAG SLUN SNAB TWIM TRIN
DULK GUSP HIFT JONT KESP LUSP MEFT MULK PILP POLD PUSP RULT SOND SUSK TIFT TULK WEND WEFT WILP ZENT BLIB BRUG BROM CLOD CLIG DROB FLUP FLIP GLIT GROB GROM PLIT PLAG PRUM SCOB SNEG SPON STOB TROM TWUN
DUSP GULT HILK JOLF KELD LUMS MELK MUSP PIMS PONT PUMS RUND SOLP SULT TILP TUST WELK WEPS WIST ZESK BLOG BRAM BRID CLAB CLOM DRAD FLAM FLOB GLUB GRAP GRIF PLOM PLUD PRAB SCAP SNAT SPUP STAP TRIB TRIF
FALP NOFT FASK LOSP DOMS ROFT JUNS DANT FUFS GILK NIND FILP YEST RONT SOSP DOLF HIFT JISK MEFT GONT FRAP GLEB KLUD TWIP PRAB SNOD GRIB BRID KREN SLIB PLOG SPET DRUF CLUG TRIF FLEP PRIB TRIN SLOM GRUT
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Nonwords and Backward Masks Used in Experiment 2 bamp conk dilt fosk gamp husp julk kosp lesk mipt nold pilt rolt sonk tand vind wemp yond zuft gant brip blod crat clin crut drap drim frim fren glap grom krim klig prob plib scim spid slaf twid tren
BIMP CANK DULT FISK GOMP HISP JILK KISP LISK MEPT NELD POLT RILT SENK TOND VUND WAMP YEND ZIFT GINT BLUP BROD CLAT CRIN CLUT DWAP DWIM FLIM FLEN GRAP GLOM KLIM KRIG PLOB PRIB SPIM SNID SCAF TRID TWEN
BALP COSK DIST FONK GALP HULP JUSK KOLP LENK MIFT NOND PIFT ROST SOSK TALD VILD WELP YOLD ZUNT GAFT BROP BLID CROT CLUN CRET DRUP DROM FRUM FRON GLIP GRUM KREM KLEG PREB PLUB SCOM SPOD SLIF TWUD TRON
BAMS CONT DILP FOST GAMS HUST JULT KOSK LESP MIPS NOLP PILK ROLP SONT TANT VINK WEMS YONT ZUFS GANK BRUT BLOM CRAF CLID CRUN DRAD DRIT FRIB FREM GLAK GROP KRIT KLIB PROG PLIP SCIB SPIB SLAD TWIK TREP
SILF DAST REMP BINT RULP FASK KASP RELT GOND LIND YASK NUSK TIST DOLF BILK JOST HONT PEFT VOND ZESP SLUB CREN PREK TRUG FLIG STIB FROB KLUG PLEN BRID TWIB SLIF DRAN GLUP BRUD CRUT DRAP GRIG SLUN FLIM
APPENDIX B Mean percentage recognition accuracy and false mask reportage of words used in Experiment 1 and Experiment 2 Word structure 2nd (C#AB) Experiment 1 (Short mask—correct) CCVC CVCC (False mask report) CCVC CVVC Experiment 1 (Long mask—correct) CCVC CVCC (False mask report) CCVC CVCC Experiment 2 CCVC CVCC Experiment 2 (False mask report) CCVC CVCC Experiment 1 (Means corrected for guessing) CCVC CVCC
Mask group 3rd (CR#B) 4th (CRA#)
Note: #s indicate replaced phonemes