Effects of stimulus duration and lsi on accuracy and transference errors in pictorial recognition

Transcription

1 Memory &: Cognition 1979, Vol. 7 (6), Effects of stimulus duration and lsi on accuracy and transference errors in pictorial recognition J. ELIZABETH BIRD and MICHAEL COOK Australian National University, Canberra, ACT2600, Australia The influence of stimulus duration and lsi on accuracy of recognition for two-part configurations was investigated in two experiments. A six-alternative forced-ehoice recognition procedure is described that tested (1) subjects' ability to recognize correct or partially correct stimuli, and (2) their tendencies to make transference errors. Subjects were significantly more accurate in recognition of pictorial components when given a longer (2-sec) rather than a shorter (.5-sec) exposure to stimuli, with lsi held constant (.5 sec). There was no beneficial effect on recognition of pictorial components when lsi was lengthened from.5 to 2 sec (with a.5-sec stimulus duration) or from.5 to 1.5 to 7 sec (with a 2-sec stimulus duration). The total time hypothesis received no support, since when two groups were given the same total time (2.5 sec for stimulus duration plus lsi), the group given the longer (2-sec) stimulus duration was significantly more accurate in partial recognition than a group given a longer (2-sec) lsi. There was a high incidence of transference errors in all experimental groups, although subjects' ability to distinguish old stimuli from distractors made by recombining parts from different targets was not affected by any of the temporal manipulations. It appeared that, although length of stimulus duration determines the number of components encoded from a picture, the encoding of information that integrates these components into a whole does not require additional processing time. The temporal course of pictorial encoding has been the subject of much investigation. Research has shown consistently that accuracy of recognition for pictures improves as stimulus duration increases from.07 to 5 sec, whether the stimuli in question are "meaningless" shapes (Hines, 1975; Mooney, 1960), realistic drawings (Madigan & Rouse, 1974; Tversky & Sherman, 1975), or photographs (Lutz & Scheirer, 1974; Shaffer & Shiffrin, 1972; Weaver & Stanny, 1978). On the other hand, there is some controversy about the effects of lengthened interstimulus interval (lsi), or blank time between items in a list, on recognition. Although Shaffer and Shiffrin (1972) first reported no increase in confidence or accuracy for recognition of target stimuli when lsi was lengthened from I to 4 sec, many other studies have found significant increases in recognition when lsi was varied in a range from.25 to 6 sec (Lutz & Scheirer, 1974; Tversky & Sherman, 1975; Weaver, 1974; Weaver & Stanny, 1978). Whatever the discrepancies between the findings of these studies, which used a variety of stimuli and testing paradigms, there is one striking agreement. None of these studies reported any significant decrease in recognition accuracy with longer ISis. Many studies 'have shown that, when other factors are held constant, delay between stimulus presentation and testing leads to decreasing accuracy of pictorial recognition (e.g., Bird, 1975; Cermak, 1971; Requests for reprints should be sent to J. E. Bird, Department of Education, Victoria University, Wellington, New Zealand. Goldstein & Chance, 1970). Therefore, since the longer lsi adds delay between the offset of the first stimulus in the list and the recognition test, it is surprising that the lists with longer ISis do not lead to inferior recognition performance. If a lengthened lsi has a facilitative effect on recognition, subjects may use this interval for processing to enhance memorial retention. The reason for the hypothesized beneficial effects of longer processing time on recognition memory is not known. Lack of knowledge about the locus of these effects may be due to the problem that traditional recognition paradigms, tested with signal detection analyses, offer little insight into the reasons for a subject's recognition choices. A different type of recognition task was used in the present study to attempt to discover more information about the influence of temporal factors on recognition. The length of time the subject has to view a stimulus may have the greatest effect on the subject's registration of the information into memory to facilitate later retrieval (Le., encoding). There are several plausible reasons for a beneficial effect of longer stimulus duration on encoding. One possibility is that the perceiver encodes the picture as a whole but requires a certain amount of exposure to the stimulus before it can be registered in memory. This view implies that there is an all-or-none encoding of each pictorial stimulus. Although it is not likely that there is a fixed temporal "threshold" required for adequate encoding of all stimuli regardless of the perceiver, it may be that, with longer stimulus Copyright 1979 Psychonomic Society, Inc X/79/ $00.95/0

2 470 BIRD AND COOK exposures, a particular perceiver is more likely to have reached threshold for a larger number of stimuli. This view would seem to be implied in the typical recognition paradigm, which measures accuracy of recognition by examining only responses to correct ("old") or incorrect ("new") stimuli. Another plausible explanation of the stimulus duration effect in recognition is that pictures are encoded in some sequential fashion and that subjects can extract more information from each stimulus the longer it is in view. This assumption seems to have been the impetus behind recent innovations in recognition testing of pictures (e.g., Klatzky & Thompson, 1975). It may be that longer stimulus durations enhance encoding through increased opportunities for the viewer to encode each part or feature of the stimulus, as well as a better chance to encode the relationships between the parts into a unitary whole. On the other hand, it is more difficult to explain a facilitative effect of a longer lsi on memory for pictures in face of powerful and usually negative effects of delay that this entails. It seems unlikely that subjects could use this interval to encode features of the stimulus that have not already been encoded or at least perceived. (Of course, this does not preclude such activity during the first 200 msec or so of the lsi, in which an icon may serve as an extended stimulus duration. The concern of this paper is with ISIs of longer duration.) Subjects may be able to use time after stimulus offset to engage in rehearsal activities in order to retain information already encoded. This, however, would be no more likely to lead to an improvement in memory than to a stable performance. Alternatively, a longer lsi might lead to an improvement in memory due to the subject's greater opportunity to integrate the information that has already been encoded. Most paradigms used to measure recognition memory do not allow for the possibility that subjects may recognize the correct components ofa previously seen stimulus without being able to recognize their correct combination as a whole picture. This possibility was suggested long ago by Bartlett (1932), who observed that subjects may remember correctly a detail seen in one picture and yet recall that it was seen in the context of a different picture. Bartlett named such confusions in memory "transference" errors. Transference errors would not be likely if a picture were registered in memory as a whole, and hence they are of theoretical importance. In the present study, a paradigm was developed to attempt to demonstrate directly the occurrence of transference errors in recognition memory. Two experi. ments were carried out in which stimuli and test sets were selected to allow measurement of the effect of interference across three stimuli presented sequentially in a list. Recognition of a stimulus was tested by asking subjects to respond to an array containing the test stimulus and five distractors, which could be either incorrect or partially correct. The pattern of errors was expected to throw new light on the source of any beneficial effect of longer stimulus durations and ISIs on recognition memory. The purpose of Experiment 1 was to attempt to replicate the established rmding (e.g., Mooney, 1960) that increasing the duration of stimuli in a list leads to more accurate recognition, and the more controversial fmding (e.g., Tversky & Sherman, 1975) that increases in lsi also lead to increases in recognition accuracy. Experiment 2 was carried out as an extension of Experi. ment 1 to examine the effects of even longer ISIs on recognition accuracy. Since the two experiments used the same materials and testing procedure, they are reported together. In Experiment 1, two brief temporal intervals (.5 sec and 2 sec) were used to investigate the effects of longer stimulus duration, lsi, and total time on the recognition process. The particular temporal durations under study were chosen in an attempt to maximize any beneficial effects of lengthening the intervals. The three experi mental groups tested were (1) a.5/.5 group given.5 sec to view each of three stimuli in a list and.5 sec between list items, (2) a.5/2 group given.5 sec for duration of stimuli and 2 sec for lsi, and (3) a 2/.5 group given 2 sec of stimulus duration and.5 sec of lsi. It was expected that, if a longer stimulus duration leads to greater accuracy of recognition for partial as well as whole shapes, the accuracy of recognition of the 2/.s group would be greater than that of the.5/.5 group. To support the prediction that a longer lsi leads to greater recognition accuracy, scores of the.5/2 group were expected to be higher than those of the.5/.5 group. Finally, Experiment 1 allowed a direct test of the "total time" hypothesis, which proposes that, within certain (unknown) temporal limits, quantitative increases in either stimulus duration or lsi lead to improved recognition (cf. Tversky & Sherman, 1975). It has been suggested that total time is effective in improving recognition only when stimulus duration is less than.3 sec (Hulme & Merikle, 1976). This could be due to truncation of the icon, which serves as an extended stimulus duration, at these very brief intervals. Experiment 1 tested the total time hypothesis with intervals greater than.3 sec. If this hypothesis is correct, a total processing time of 2.5 sec for each stimulus (the.5/2 and 2/.5 groups) should lead to greater recognition accuracy than would a total time of 1 sec (the.5/.5 group). If, however, stimulus duration is more important than total time at these intervals, subjects in the 2/.5 group should be more accurate than subjects in the.5/2 group, even though both groups have the same total time to process each stimulus. Experiment 2 provided another test of the hypothesized facilitative effect of longer ISIs on recognition memory using the longer fixed stimulus duration of Experiment 1 (2 sec). If there is some "optimal ratio" between stimulus duration and lsi that varies depending on the particular stimuli under consideration (cf. Aaronson, 1967), then it is possible that a very brief stimulus duration might prohibit a demonstration of the

3 PICTORIAL RECOGNITION 471 beneficial effect ofa longer lsi. For this reason, a different stimulus duration control was used in Experiment 2. After extensive pilot testing, ISIs of 1.5 and 7 sec were chosen for comparison in the experiment. It was predicted that a 2/1.5 group given a 2-sec stimulus duration and a 1.S-sec lsi would be less accurate in partial and holistic recognition than would a group given the same 2-sec stimulus duration with 7-sec lsi (the 2/7 group). Similarly, it was expected that the 2/1.5 group would be more accurate in recognition than would the 2/.S group of Experiment 1. METHOD Subjects Volunteers for Experiment 1 were 51 students in an introductory psychology course at the Australian National University. Equal numbers of subjects were assigned randomly to each of the three experimental groups, the.5/.5,.5/2, and 2/.5 groups. A further 28 subjects from the same pool of introductory psychology students volunteered to be in Experiment 2 and were assigned randomly to the 2/1.5 and 2/7 groups. One subject in the 7-sec group failed to follow instructions about responding and was rejected from analysis. A randomly selected subject in the 2/1.5 group was rejected to equate the number of subjects (13) in each group of Experiment 2. Apparatus In Experiment 1, the presentation of the three pictures in each list was accomplished with three slide projectors that were arranged side by side so that they projected slides onto the same area of a back-projection screen. The visual angle for subjects was 14 deg. A modular, digital, electronic timing device was connected to three solenoid shutters, enabling the shutters to be opened in succession for specified time intervals and providing control of the interval between the closing of one shutter and the opening of the next in the sequence. Each shutter was mounted in front of the lens of one of the projectors. One of the projectors was used to present slides of the test series after each list of three stimuli was shown. In Experiment 2, presentation of the stimulus lists was accomplished with a single slide projector installed with an electronic timing device to display a fixed number of slides for a specified stimulus duration and lsi. Another slide projector was placed next to the fltst to project the test sets onto the back-projection screen in approximately the same area. Although the arrangement of slide projectors was somewhat different for Experiments 1 and 2, it was not thought that subjects in the two experiments had differing experiences with the memory task. Procedure Subjects were tested individually in a dimly lit room. For each recognition trial, subjects fltst viewed a list of three successive two-part shapes. Each shape was presented for a specified interval (the stimulus duration for that experimental group). After presentation of each of the fltst two shapes, a blank screen was presented during the specified lsi to separate successive stimuli. After the third shape in a list was presented, there was a delay of 5 sec of blank screen before the fltst sixitem recognition test array was shown. For each array, subjects were asked to circle, on an answer sheet provided, one. of six dots arrayed in a matrix corresponding to the test array of six shapes. For each choice, subjects were asked to use a 3-point scale to rate their confidence that the interior part, exterior part, and the whole combination, respectively, had been presented. After subjects had made a response to this set, the second and fmal recognition set was shown and tested in the same manner. A practice list of three stimuli similar to the test shapes was presented to subjects before the test trials. Practice stimuli were presented at the same stimulus duration and lsi to be used for the test trials and were tested with the same procedure outlined above. After the practice trial, subjects were given eight test trials. The orders of lists of stimuli, the stimuli within lists, and their corresponding test arrays were randomized for each subject. Materials In order to minimize labeling and other mnemonic techniques subjects might use to overcome any tendency toward transference, pictures chosen as stimuli were abstract shapes rather than clearly representational drawings. The shapes used were symmetrical drawings containing an exterior 24-sided, biaxially symmetrical polygon and a bilaterally symmetrical interior component made of six line segments. Two judges combined the parts together so that no combination formed an obvious representation of a real object. A pool of 60 items was thus created. Shapes generated by a random method were not used, as it was expected that this would make the task too difficult. Also, the symmetry in the shapes chosen reduced their complexity (cf. Chipman, 1977) and produced shapes with the redundancy found in more meaningful stimuli, such as faces or leaves. Sets of three items were then selected so that the items and their parts would be easily discriminable. To choose sets of dissimilar items, five judges were fltst shown all 60 shapes. On the basis of their sortings, 20 shapes that were extremely similar to other shapes were omitted. The 40 remaining shapes were presented as a randomly organized array of cards to an additional 10 judges, who were asked to make two sorts of the shapes (counterbalanced across judges) on the basis of similarity, once for the interiors of the shapes and once for the exteriors. Based on the sortings, eight sets of five shapes were chosen so that they were lowest in similarity of both interior and exterior parts. In each of the sets, three of the shapes were randomly chosen as stimuli for presentation and two were chosen as distractors. Of the three stimuli, two were chosen (randomly) as target items. The remaining stimulus was not tested; its liarts were separated and recombined with parts of the other mapes in the set to form distractors. Figure 1 gives an example of a stimulus set consisting of items a and b, to be tested in recognition, and item c, not tested. Arrays of six pictures were created for recognition testing of items a and b (shown in Figure 1 as Test Sets 1 and 2, respectively). Each test picture can be designated as an "XX" item, in which the fltst letter denotes whether the interior of the shape is old (0) or new (N), and the second letter refers in similar manner to the exterior. The superscript (') is added to denoted parts of old items that were not tested in recognition but instead were used to create distractors. Thus, the six items in each test set were (1) the original old shape (00), (2) two old parts recombined into a new whole (00' or 0'0), (3) the interior of the original shape tested recombined with a new exterior (ON), (4) a new interior combined with the exterior of the original shape (NO), (5) combination of the two new parts into a whole (NN), and (6) combination of the part taken from the untested stimulus mentioned in Item 2 with one of the new parts (NO' or O'N). Two test sets were created to test recognition for each list of three shapes. One set contained 00' and NO' items; the other contained 0'0 and O'N items. Thus, in each set, a single part occurred two or three times, balanced across pairs of test sets. Three shapes similar to the test shapes were created to give subjects practice with the testing procedure. Practice shapes consisted of a symmetrical 4-line-segment interior enclosed within a 16-sided polygon. Two practice sets were made in the same way as the recognition test sets, with the exception that each 00' (or 0'0) item was replaced by a new NO' (or O'N) item in order to avoid emphasis on transference errors and to reduce the difficulty of the practice trials. The 24 stimuli, 3 practice stimuli, and 18 test sets were photographed and reduced to 35-mm negative slides. The presentation of white-on-black figures reduced the contrast and

4 472 BIRD AND COOK Stimulus '-..././ "- l~~, oo~. Figure l. Example of a stimulus list and its two recognition test sets. resulting glare from the projectors in order to reduce subjects' fatigue. RESULTS Data for Experiments 1 and 2 were analyzed together. 1 Means and unbiased standard deviations of proportions of responses to the 00, 00' (including 0'0), and NN items are shown in Table 1 for each group. Also shown are proportions of responses to ON (including O'N) and NO (including NO') items. Since there were three items with one old part in each test C set, proportions of ON and NO responses were corrected so that they could be compared directly with proportions of responses to other types ofitems; that is, proportions of ON and NO responses were each reduced by one-third. There was a dependency between proportions of responses to different test items, since subjects made only one response to each test set. Thus, it was not possible to make independent comparisons of all types of responses across the five groups. Three accuracy scores were calculated for each subject, based on his or her responses over all sets. To test whether subjects were more likely to recognize both parts of stimuli rather than a single part, an accuracy score was created by subtracting the corrected proportion of responses to ON and NO items from the proportion of responses to 00 and 00' items and dividing this by the total proportion of 00,00', ON, and NO responses. These "accuracy of parts" (AOP) scores were expected to range from 1, indicating that subjects chose some items with two correct parts and no items containing only one correct part, to 0, indicating that subjects chose items with either one or two correct parts indiscriminately. Zero scores would suggest that the subject remembered only one part of the shapes correctly. Means and standard deviations of AOP scores are shown in Table 1 for each group. To maintain a family-wide Type I error rate (twotailed) of.05, Dunn's multiple-comparisons procedure (Kirk, 1968) based on 72 degrees of freedom was used to analyze six pairwise differences in AOP scores between the five experimental groups in Table 1. First, scores of the.5/.5 and 2/.5 groups were compared to see whether an increase in stimulus duration would lead to a greater tendency to recognize correct parts of the shapes. The 2/.5 group had a significantly higher mean AOP score than did the.5/.5 group. Thus, increasing the stimulus duration from.5 to 2 sec, with lsi held constant at.5 sec, led to an increase in recognition of both parts rather than of a single part of each shape. The total time hypothesis was tested by considering the similarity between the 2/.5 and.5/2 groups in comparison with the other groups given more or less total time. The 2/.5 group had a significantly higher mean Table 1 Means and Unbiased Standard Deviations of Proportions of Responses to the Recognition Test Items and Two Accuracy Scores for Each Group in Experiments 1 and 2 Experiment 1 Experiment 2.5/.5.5/2 2/.5 2/1.5 2/7 Response/ Score Mean SO Mean SO Mean SO Mean SO Mean SO ' ON NO NN AOP CCP Note-Groups are defined as stimulus duration/lsi (in seconds). AOP =accuracy ofpartial recognition; CCP =recognition ofco"ect combinations ofparts.

5 PICTORIAL RECOGNITION 473 AOP score than did the.5/2 group, giving no support to the total time hypothesis. Length of stimulus duration rather than total time per se appeared to determine the recognition of both parts rather than of a single part of the shapes. The hypothesis of a facilitating effect of longer ISis on recognition was tested by comparing groups given the same stimulus duration but with differing ISis. The mean AOP score of the.5/.5 group did not differ significantly from that ofthe.5/2 group. Further, the mean AOP scores of the 2/.5, 2/1.5, and 2/7 groups did not differ significantly from each other. These findings gave no support to the lsi hypothesis. There was no indication that increasing the lsi from.5 to 7 sec increased subjects' tendencies to recognize both parts of the shapes. A second analysis of recognition accuracy was carried out to investigate the large number of transference errors made by subjects in both experiments. Subjects chose distractors made by recombining old parts into a new whole (00' items) on about one-quarter of the trials. As a measure of the tendency toward transference errors, a correct combination-of-parts (CCP) score was calculated for each subject by subtracting the proportion of 00' responses from the proportion of 00 hits and dividing this number by the accumulated proportions of both 00 and 00' scores. This score indicates the tendency for the subject to choose an old stimulus, given that the subject could recognize constituent parts of old stimuli. Scores were expected to range from 1, indicating accurate recognition with no transference errors, to 0, indicating an extreme effect oftransference errors on recognition due to subjects' inability to distinguish correct combinations of old parts from incorrect combinations. Means and standard deviations of CCP scores are shown for each group in Table 1. Differences between pairs of groups in mean CCP scores were analyzed with the same Dunn's comparisons procedure outlined above. None of the contrasts was significant. The tendency to make transference errors did not appear to be affected by the temporal parameters manipulated. The proportion of responses to distractors with no old parts (NN distractors) was higher in the.5/.5 group than in the other groups. Means reported in Table 1 show that subjects in every experimental group tested chose completely new distractors on only 3% to 4% of occasions, with the exception of the.5/.5 group; the latter subjects chose NN distractors about twice as often as subjects in other groups given longer stimulus durations or ISis. The greater tendency for subjects in the.51.5 group to guess may have spuriously inflated their accuracy scores, thus diminishing any difference in accuracy between this group and the group given a longer lsi (the.5/2 group). For this reason, a third analysis of accuracy was carried out, creating a total accuracy score by subtracting the total proportion ofall responses to distractors from the relative proportion of hits (Le., 00 responses were multiplied by five). The results of this analysis merely replicated those of the AOP score analysis. The two scores are, of course, closely related. However, this third analysis does indicate that when the guessing rate is taken into account (by inclusion of NN responses), the results are not markedly changed. Subjects given 2 sec stimulus duration could recognize more parts of the shapes (AOP scores) and more whole shapes (total accuracy scores) than could subjects given.5 sec to view each shape, even when subjects given the shorter viewing time were given longer ISIs so that total time per stimulus was comparable. There was no significant difference between proportions of ON and NO responses in the.51.5 group [t(16) < 1], the.5/2group [t(16) = 1.16],the 2/.5 group [t(16) = 1.36], the 2/1.5 group [t(12) =1.12], or the 2/7 group [t(12)<i] (all ps<.05,two-tailed test). That is, distractors with new exterior parts were chosen as often as distractors with new interiors. This suggests that subjects were able to retain information about one part of each stimulus even when given only 1 sec of processing time, although subjects did not seem to be biased toward remembering a particular part of each shape. This is consistent with the contention that subjects were not attending to the parts in a fixed sequence. Confidence ratings in the experiments suggested that subjects had insight into the accuracy of their recognition choices. Subjects were more confident about 00 responses than about choices of items containing one new part, and their confidence was lowest for choices of NN distractors. DISCUSSION Results of the present study give support to the fmdings of previous researchers (e.g., Mooney, 1960) that longer stimulus durations lead to increasing accuracy of pictorial recognition. Furthermore, the present fmdings point to an increasing tendency to recognize constituent parts of stimuli as the locus of the beneficial effect of lengthened stimulus viewing time. As predicted, Experiment 1 showed that increasing stimulus duration from.5 to 2 sec leads to an increasing tendency to recognize both parts of a two-part shape rather than a single part. The unexpected finding was that stimulus duration did not affect subjects' tendencies to recognize the correct combinations of the parts of each shape; the rate of transference errors observed was unaffected by stimulus duration. These results, taken together, suggest that the facilitative effect of longer stimulus duration on recognition is due to better encoding of pictorial components rather than to their integration. It might be argued that, given longer stimulus durations, subjects would encode integrative as well as componential information during viewing time. It is interesting to note that, in a small pilot study using these stimulus materials, there was a significant increase in rec~tion of both parts rather than of a single part of the shapes when stimulus duration was lengthened from 2 to 5 sec (with a constant 1.5-sec lsi), although again,

6 474 BIRD AND COOK there was no significant decrease in transference errors over the same interval. These findings replicate those of Experiment 1, while extending the range of stimulus durations tested with the present stimuli from.5 to 5 sec. It appears that the facilitative effect of a longer time to view the stimulus is due to better encoding of all the parts of each shape. The encodingof integrative information that links the relevant parts of a stimulus together in memory in order to prevent transference errors may not require any additional processing time, at least within the first 5 sec of viewing time. Even subjects given only.5 sec to view each stimulus (Experiment I), who had the lowest hit rate of all the experimental groups, were no more likely to confuse transference distractors with target items than were subjects given 2 sec stimulus duration. The findings of the present study did not add any support to the controversial hypothesis (e.g., Tversky & Shennan, 1975) that recognition memory for pictures increases with longer ISIs. Neither subjects' tendency to recognize both parts of the stimulus shapes nor their tendency to integrate this infonnation was influenced significantly by increases in lsi over a range from.5 to 7 sec. These findings are consistent with the notion that subjects have difficulty encoding new information about a stimulus once it has been removed from view. On the other hand, the lsi may be used productively to maintain in memory infonnation about the stimulus that has already been encoded. Given that the present experiments used novel configurations presented for very brief intervals, it is indeed surprising that longer ISIs did not lead to a decline in recognition memory. With more representational pictures, it might be hypothesized that subjects have greater opportunities for verbal rehearsal during the lsi that could be used to enhance recognition. However, as discussed earlier, this would not necessarily overcome the negative effect of lengthened delay before testing that longer ISis produce. In order for the lsi to be used to facilitate recognition, new infonnation or better integration of existing information would need to be encoded during this interval. At present, there is little information to indicate just what is being encoded in the intervals between presentation of representative pictures. The demonstration of transference errors in recognition in the present study gives no support to the contention that pictures are encoded in an all-or-none fashion. On some occasions, the subject may remember only fragments of a picture. On other occasions, the subject may construct a confluent whole from fragments seen in different contexts. The question that needs to be answered is, how do observers of pictures manage to separate the fragments viewed in one picture from fragments viewed in another? With certain meaningful line drawings, there is evidence that subjects have preferences about the organization of parts that constitute a pattern (Reed, 1974; Reed & Johnsen, 1975). There is further evidence that some of the expectations (i.e., of what fragments the whole was composed) may follow Gestalt laws regarding the perception of fonn (Bower & Glass, 1976). Representative drawings or photographs may allow subjects more opportunities to provide links between the parts of a configuration so that they can be retrieved as a connected organization rather than as disconnected fragments. An understanding of conditions that produce transference errors could help to specify the structure of interfragment connections in memory for pictures and other visual stimuli. REFERENCES AARONSON, D. 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7 PICTORIAL RECOGNITION 47S WEAVER. G. E., & STANNY, C. J. Short-term retention of pictorial stimuli as assessed by a probe recognition technique. Journal of Experimental Psychology: Human Learning and Memory, 1978, 4, NOTE 1. We would like to thank an anonymous reviewer for making the suggestion that results of the two experiments should be analyzed together. which allows a comparison of groups given a constant 2-sec stimulus duration with ISIs varying from.5 to 7 sec. The results of this combined analysis replicate those of the separate analyses carried out for each experiment. (Revision accepted for publication September 5,1979.)