The development of visual encoding and retention skills

JOURNAL

OF EXPERIMENTAL

The Development

CHILD

PSYCHOLOGY

30, 88-97 (1980)

of Visual Encoding and Retention Skills E. HUBA

MARY Iowa

State

University

AND FRANK State

University

of New

York

R. VELLUTINO at Albany

and Albany

Medical

College

The development of the ability to visually encode and maintain a visual stimulus was examined in a paradigm in which verbal encoding of the stimulus was prevented. The 8-, 12-, and 21-year-old subjects participated in a shadowing task during which they viewed a letter which was visually presented for 200 msec, 5 set after the shadowing list began. On each trial subjects either reported the letter immediately after presentation or continued shadowing for 4 or 10 sec. Although results replicated those found in previous research using the paradigm, no age differences were found in recall accuracy, types of errors, or introspective reports describing perceived recall strategy. These findings suggest that even 8 year olds were able to employ a visual code and retain it for several seconds in a situation in which incentive to do so was provided.

It has been asserted that visually presented information is necessarily encoded auditorily in short term memory before it is used by an individual (Conrad, 1972). A number of recent studies, however, have demonstrated that when adults process a visually presented stimulus, they are able to encode it visually (Kroll, 1975; Meudell, 1972; Nickerson, 1976; Scarborough, 1972). Posner, Boies, Eichelman, and Taylor (1969) have suggested that subjects employ such encoding when it is to their advantage to do so. That is, in certain circumstances visual encoding may be a more efficient strategy to employ in completing a task than verbal encodThis research formed part of a Ph.D. dissertation submitted to the Department of Educational Psychology and Statistics, State University of New York at Albany under the supervision of Dr. Frank R. Vellutino. It was partially supported through a grant to the second author from the National Institute of Child Health and Human Development Grant lROlHDO965801. The authors wish to thank Donna Scanlon, Sylvia Durban, and the research staff at the Child Research and Study Center, Albany, N.Y., for screening and scheduling subjects. Requests for reprints should be sent to Mary E. Huba. 206A Curtiss Hall, College of Education, Iowa State University. Ames, Iowa 50011. 88 0022-0965/80/040088-10$02.00/O Copyright 0 1980 by Academic Press, Inc. All rights of reproduction in any form reserved.

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ing. Although questions concerning the development of such flexible processing are of interest, few studies have addressed them (Hoving, Morin, & Konick, 1974; Morrison, Holmes, & Haith, 1974). Furthermore, available data do not clearly specify the conditions under which children can form a code which contains only visual information and subsequently maintain it. Morrison, Holmes, and Haith (1974) suggested that 5 and 8 year olds in their study did not maintain a visual code. Their subjects were cued to report a portion of a briefly presented stimulus array after a cue delay which varied in length up to 1000 msec. The performance of 5 year olds was inferior to that of adults at all cue delays, whereas the performance of 8 year olds was inferior only at delays between 450 and 1000 msec. Thus the authors inferred that a visual retention strategy was not used successfully by these younger subjects. Although there was no assurance that any subjects were even attempting to employ this strategy, it is not unreasonable to hypothesize that it would have been advantageous to them to do so. Hoving, Morin, and Konick (1974) examined visual encoding and retention using a modification of the Posner matching paradigm (Posner & Mitchell, 1967). Results demonstrated that at a 700-msec interstimulus interval 5 and 9 year olds correctly matched physically identical stimuli faster than they matched categorically identical stimuli. In the context of previous research (Posner & Taylor, 1969), this finding suggests that their physical matches were based on visual rather than verbal information, and indicates that in this paradigm young children did use a visual code. The present study attempted to extend the findings of Hoving et al. and Morrison et al. by employing a paradigm developed by Kroll and colleagues (Kroll, 1975). This approach, they assert, successfully isolates visual encoding from verbal encoding, and creates incentive for its use well beyond the relatively brief intervals used in the Posner paradigm. Each subject is shown a letter while she/he is shadowing (repeating) a series of rapidly spoken letters. It is assumed that the subject must rehearse this memory letter in order to retain it. Since she/he is encouraged to maintain accuracy in shadowing and thus is required to devote considerable attention to it, recoding the stimulus (memory letter) is assumed to be difficult, if not impossible (Kroll, 1975). Briefly, the task is as follows. A subject begins shadowing letters stated by a female voice, the memory letter is flashed on the screen, and, after its presentation, the subject shadows letters which sound either similar or dissimilar to the memory letter name. Subjects who are able to retain the memory letter for the duration of the retention interval without engaging in verbal encoding should not be adversely affected by shadowing similar sounding letters. That is, memory letter recall should not differ under high and low similarity conditions. If subjects do say the name of the stimulus

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to themselves, stimulus recall should suffer under the high similarity condition. The latter prediction is tested by including an auditory presentation condition in which one shadowing letter is stated by a male voice. Subjects recall this letter which they have shadowed and thus have verbally encoded. The present study used this approach in order to compare the use of a visual code across age groups. It was expected that Kroll’s findings with adults would be replicated and thus form a basis against which the performance of younger subjects could be compared. The current study was seen as similar to that of Hoving et al. in that both tasks include conditions in which the use of visual encoding and retention is clearly advantageous. Therefore on the basis of Hoving et al.‘s findings it was hypothesized that in this study 8 year olds would be as competent as 12 year olds and adults at recalling a visual memory letter when verbal encoding was prevented. In order to compare the length of time for which subjects of different age groups could remember the letter, the retention interval variable included three levels: 0, 4, and 10 sec. Thus, for subjects who were able to form a visual code after stimulus presentation, the opportunity was provided for retaining it for several seconds beyond the 700 msec used by Hoving et al. METHODS Subjects

Subjects for the experiment were 10 second graders (mean CA = 8.0 years, SD = 0.4 years), 10 sixth graders (mean CA = 12.1, SD = OS), and 16 college volunteers (mean CA = 21.2, SD = 1.9). Second and sixth graders were sampled from both public and parochial schools in the Albany, Schenectady, and Troy, N.Y. area, and as measured by the Slosson Intelligence Test (Slosson, 1963), were of at least average intelligence (M = 119, SD = 9.3 and M = 120, SD = 5.4, respectively). According to teacher judgments and word recognition scores on the Gilmore Oral Reading Test (Gilmore, 1968), all subjects were progressing in an age appropriate manner in academic activities. Apparatus

Shadowing lists were presented to subjects binaurally via one track of a Sharp stereo cassette tape deck (RT-1155). On half the tapes a signal on the other track activated a voice-keyed microphone which in turn controlled the opening of a Campden Instruments Ltd. two-channel tachistoscope (Cl-610) for a 200-msec presentation of the visual memory letter 5 set after the shadowing list began. Materials

Materials were designed to correspond as closely as possible to those used by Salzberg, Parks, Kroll, and Parkinson (1971). Stimuli were drawn

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from a pool containing two groups of phonemically similar letters (J, K, A) and (S, F, X). Shadowing lists, recited by a female voice, consisted primarily of randomly selected letters from the set C, D, I, 0, P, Q, R, T, U, and Y. On high similarity lists the two remaining letters in the phonemic group from which the stimulus was chosen were placed randomly in every other letter position during the first 4 set after stimulus presentation. In low similarity lists those positions were randomly filled by two letters from the other phonemic group. Shadowing lists to be used during shadowing training were composed of randomly selected letters of the alphabet, as were stimuli on these trials. Visual stimuli were block capital letters, 1 in. in height, printed on beige cards. They subtended a vertical visual angle of 2.9”. On half the tapes, presentation of the auditory stimulus was made possible by substituting a male voice, stating the memory letter, for the shadowing letter which occurred 5 set after the list began. Procedure

In this experiment subjects were simultaneously engaged in two tasks: recalling a memory letter and shadowing a series of letters. On every trial each subject was presented with one of two presentation modalities (visual, auditory), one of three retention intervals (0,4, and 10 set), and one of two similarity conditions (high, low). Subjects received six trials under each of the 12 conditions which resulted from the factorial combination of these independent variables. During an initial session, subjects first learned to shadow. All adult subjects received shadowing training on lists presented at the rate of two letters per second. Second and sixth graders were initially asked to shadow lists presented at 1, l), and 2 letters per second. They were trained at the fastest speed at which they could reach the 80% accuracy criterion. (Previous research (Kroll, 1975) has assumed that when the shadowing list is presented at a speed which allows only 80% accuracy, so much of an adult subject’s attention is required to maintain this accuracy that she/he cannot verbally encode a visual stimulus.) After shadowing training, subjects practiced the experimental task for 18 trials. On each trial, the memory letter was presented 5 set after shadowing began. Subjects either terminated shadowing immediately or continued for 4 or 10 sec. They wrote down the memory letter when the shadowing list ended. During each of two experimental sessions, subjects received 18 trials presented in a random order in each modality. The two modality conditions were presented in blocks which were counterbalanced across subjects. Within each modality series, each subject received his/her own random order of trials with the restriction that no experimental condition was repeated until all others had been presented. Before each modality

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block, subjects participated in one warm-up trial. Instructions emphasized the importance of maintaining shadowing accuracy throughout the list. At the conclusion of the experiment, the subject was asked, “How did you remember the letter that flashed on the screen when you couldn’t write it down right away?” Analysis Two scores were computed for each subject: the number of errors in recalling the memory letter (the maximum possible in each of the 12 experimental cells was six) and the number of shadowing errors (omissions, substitutions, and insertions). Prior to the analysis each subject’s number of shadowing errors (all types combined) had been converted to a common base: count per unit time. Each set of data was analyzed separately. Data were subjected to a 3 x 2 x 3 x 2 (age x memory letter modality x retention interval x similarity) analysis of variance with repeated measures on all variables except age. Since similarity conditions were not present under the 0-set delay interval, this interval was not included in the analysis of similarity effects. Although data were transformed by both logarithmic and square-root transformations to insure that the assumptions of analysis of variance were met, results in each case were virtually identical to those obtained with raw data. Thus the latter are reported. Memory letter errors were classified in terms of dimensions such as membership in the memory letter set, visual or auditory similarity to the memory letter, etc. Patterns of error frequency were compared across ages. Responses to the question asked at the end of the experiment were reviewed and grouped by similarity of content. RESULTS

The primary prediction of this study was supported by the data: no age differences were found in visual memory letter recall. Neither were age differences found in auditory memory letter recall. The mean number of memory letter recall errors of 8-, 12-, and 21-year-olds, respectively, were 1.09, 1.41, and 1.15, yielding an insignificant main effect of age, F(2, 33) = .7 1. In addition, the age variable did not interact with any other factor(s); the largest F ratio observed for an interaction effect (age x similarity) was F(2, 33) = 1.55,~ = .23. These results show that 8 and 12 year olds were as efficient as adults in memory letter recall at all three retention intervals. Most importantly, they were able to encode and retain the visually presented stimulus for up to 10 set when verbal encoding and rehearsal were prevented. Furthermore, no differences between age groups were found when frequencies of errors in various error categories were compared. Thus, results replicate previous findings with adults which demonstrate that for them verbal encoding is not a necessary requirement for stimulus

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recall, and they allow one to extend this assertion to subjects of two younger age groups. Overall results were virtually identical to those found in previous research with adults (Kroll, 1975). Specifically, subjects made more errors when the memory letter was presented auditorily than they did when it was presented visually, F(1, 33) = 24.89, p < .Ol. Errors increased when shadowing letters were highly similar, rather than dissimilar, to the memory letter name, F(l, 33) = 7.47, p < .Ol. Finally, errors increased when subjects were required to delay report of the memory letter for longer retention intervals, F(2, 66) = 85.82, p < .Ol. Figure 1 adds further detail. It shows that while subjects made no more errors under the auditory presentation condition than under the visual presentation condition at the 0-set retention interval, they made increasingly more errors in the auditory condition at 4 and 10 set, F(2, 66) = 19.52, p <.Ol. Figure 2 indicates that similarity exerted its effect only under the auditory condition and had no effect under the visual condition, F( 1, 33) = 9.44, p < .Ol. These findings validated the assumption that in this paradigm subjects are prevented from verbally encoding a visually presented stimulus. Further, they demonstrated that the paradigm is a viable approach for the assessment of visual information processing in children. Finally, it should be noted in support of the null hypothesis regarding age differences, that all main effects, as well as the modality x retention interval interaction, were replicated when the data of the 10 second graders were analyzed separately. In their data the modality x similarity interaction, F( 1, 9) = 2.58, p = .14, was not statistically significant, but the pattern of means was as predicted. The primary results from the analysis of shadowing data indicated, first, 3

MODALITY: AUDITORY

W

VISUAL M

RETENTION

1. presentation FIG.

Mean number and retention

of memory interval.

INTERVAL

letter

recall

(SECONDS)

errors

as a function

of modality

of

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3

SIMILARITY:

r

HIGH 0 LowI P 0

2

E a z

I

i

0 VISUAL

AUDITORY MODALITY

FIG. 2. Mean number of memory letter recall errors as a function of modality presentation and similarity of shadowing list to the memory letter name.

of

that no age differences were found in shadowing accuracy, F(2, 33) = 1.84. Second, the number of shadowing errors increased more rapidly under the auditory condition as the retention interval increased, F(2, 66) = 6.95, p < .Ol. These findings lend support to memory letter recall results by suggesting that all subjects performed the task as directed. Introspective reports added complementary information to statistical findings. A large proportion of subjects in each age group (63,22, and 50% of the 8, 12, and 21 year olds, respectively) reported that their sole strategy for recalling the visual memory letter consisted of picturing it throughout the retention period, or at least initially. When one adds to these subjects those who reportedly used picturing as their primary strategy, supplemented at times by naming or associating, one accounts for 75, 55, and 6% of the age groups. The remaining subjects indicated that they relied primarily on making associations to the stimulus, or in some cases, naming it. Despite the fact that introspective reports should be interpreted with caution, the immediacy and vividness of the reports of some second graders lent credence to their reliability. When asked how they remembered the visual stimulus, they replied with statements that included, “I just write it down in my mind”; “You’d put it in your mind, you’d think how it looked”; “I pretend it’s a flashing letter and I look at it”; “I drew it: in the back of my mind there’s a big drawing board with a thousand pieces of paper and a magic pencil.” DISCUSSION

This experiment demonstrated that under certain circumstances children as young as 8 years old can utilize visual information which has not

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been verbally encoded. Specifically, no age differences were found in recalling the visual memory letter while engaged in the concurrent verbal task. Second and sixth grade children were as capable as adults in retaining the visual memory letter for up to 10 set under conditions which assumedly prevented them from recoding it. The simultaneous processing of auditorily confusable information had no effect on their recall of visually presented stimuli, while it did exert a debilitating effect on recall of information which of necessity was verbally encoded upon presentation (auditory memory letters). This suggests that, like adults, these younger subjects were able to employ alternate procedures for the retention of the visual memory letter for intervals clearly beyond the range of iconic memory (Sperling, 1960). This interpretation results from a failure to reject the null hypothesis of no differences when age contrasts were examined statistically. Although such a finding could result from a lack of sufficient power to reject the null hypothesis, the finding of other significant differences in this study suggests that power was sufficiently great. Further support for the null hypothesis comes from the similarity of the age groups when other aspects of their performance were examined. For example, 8, 12, and 21 year olds did not appear to differ in their reported manner of retaining the visual memory letter. About 50 to 75% of subjects in each age group reported using a strategy which relied primarily on picturing the stimulus, whereas smaller proportions indicated that they relied chiefly on making associations to the stimulus or naming it. In a general sense, this corresponds with the reports of Kroll’s adult subjects (Kroll, Parks, Parkinson, Bieber, & Johnson, 1970) who relied mainly on maintaining a visual “after image” but on occasion reported naming or associating to the stimulus. Subjective reports such as these suggest that the shadowing task may not prevent verbal encoding of the memory letter on every trial for every subject. When types of memory letter recall errors were analyzed, the groups showed similar patterns of proportions of errors in the error categories. This would appear to result from their similar response to stimulus materials and suggests comparable strategies for attempting to retrieve the memory letter once it had been forgotten. No age differences were found in any aspect of shadowing performance when error data were converted to count per unit time, and the assumption was made that the task “taxed the attentional capacity” of each group to a similar degree. The only age difference which was noted manifested itself in the preexperimental session when subjects were assessed for the ease with which they could shadow letters presented at varying rates. Within group differences, as well as between group differences, were noted. Although all adults were assigned to the 2 per second rate on the basis of previous research (Kroll, 1975), striking individual differences were noted in their shadowing facility at this rate. The perfor-

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mance of some subjects was markedly error free, while that of others was labored and faulty. Similar individual differences were noted among members of both sixth and second grade groups, all of whom were assigned to a 1% per second rate (with the exception of one second grader assigned to a 1 per second rate). Remarkably, however, no subject in either of the younger groups, however talented at the task, was able to shadow at the 2 per second rate. Thus, an age difference between elementary school children and adults did emerge prior to the experiment in their ability to orally reproduce rapidly presented letters. No such difference was found, however, between the second and sixth grade groups. In summary, no age differences were observed among 8, 12, and 2 1 year olds in memory letter recall accuracy, shadowing accuracy, reported strategy for remembering the visual memory letter, or types and patterns of errors. These results extend the findings of Hoving et al. (1974) mentioned earlier. It will be recalled that they found that 8 year olds, like adults, were able to maintain a visual code for 700 msec in order to facilitate rapid matches of physically identical stimuli. The current study demonstrates that in certain circumstances 8 year olds can maintain this code for up to 10 sec. Since, however, Morrison et al. (1974) describe a situation in which visual encoding was not successfully employed by 8 year olds, one might speculate about the variables which may control its use. It may be that subjects in the current study and in the Hoving task were provided with the incentive to employ visual processing strategies, while those in the Morrison et al. study were not. That is, subjects in the former studies, in contrast to those in the Morrison et al. study, may have employed visual encoding as an atypical mode of processing in order to fulfill task demands more efficiently. The performance of 8 year olds within the Kroll paradigm used in this study does suggest that in a specific situation they are able to choose a mode of processing suited to their current purpose. A more likely explanation for Morrison et al.‘s results is that younger subjects find it more difficult than adults to visually encode and maintain the multiple stimuli used in a partial report paradigm. Thus, 8 year olds may have been able to visually encode the single stimuli used in both the current study and the Hoving et al. study. They may have been impaired, however, by a lack of facility in applying this strategy to the multiple stimuli used by Morrison et al. The results of Blake (1974) make this conjecture plausible. She showed one-, two-, and four-item arrays to 8 year olds and adults for brief durations similar to those in the studies under discussion. Although visual encoding was not being studied directly, the task appears to be one in which it could be profitably employed. Blake found that 8 year olds were inferior to adults in recall accuracy only with four-item arrays. If one could correctly assume that

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subjects attempted to utilize a visual code to promote recall, logically follow that this was an effective strategy for 8 year olds one- and two-item arrays. Thus, it may be productive for future to examine the effect of stimulus array size on efficient use encoding in subjects of different ages.

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it would with only research of visual

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change in visual information processing under backward masking. Child Psychology, 1974, 17(l), 133-146. Conrad, R. Speech and reading. In J. F. Kavanagh and I. G. Mattingly (Eds.), Language by ear and by eye. Cambridge, Mass.: MIT Press, 1972. Gilmore, J. V. Gilmore Oral Reading Test. New York: Harcourt, Brace, and World, 1968. Hoving, K. L., Morin, R. E., & Konick, D. S. Age related changes in the effectiveness of name and visual codes in recognition memory. Journnl ofExperimentnl Child Psychology, 1974, 18, 349-361. Kroll, N. E. A. Visual short-term memory. In D. Deutsch and J. A. Deutsch (Eds.), Short ferm memory. New York: Academic Press, 1975. Kroll, N. E. A., Parks, T., Parkinson, S. R., Bieber, S. L., & Johnson, A. L. Short term memory while shadowing: Recall of visually and of aurally presented letters. Journal of Experimental Psychology, 1970, 85(2), 200-224. Meudell, P. D. Short-term visual memory: Comparative effects of two types of distraction on the recall of visually presented verbal and nonverbal material. Journal ofExperimenJournal

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Morrison, F. J., Holmes, D. L., & Haith, M. M. A developmental study of the effect of familiarity on short-term visual memory. Journal of Experimental Child Psychology, 1974, 18, 412-425. Nickerson, R. S. Short-term retention of visually presented stimuli: Some evidence of visual encoding. Acta Psychologica, 1976, 40, 153-162. Posner, M. I., Boies, S. J., Eichelman, W. H., & Taylor, R. L. Retention of visual and name codes of single letters. Journal of Experimental Psychology Monograph, 1969, 79(l), l-16. Posner, M. I., & Mitchell, R. F. Chronometric analysis of classification. Psychological Review, 1%7, 74, 392-409. Posner, M. I., & Taylor, R. L. Subtractive method applied to separation of visual and name components of multiletter arrays. Acta Psychologica, 1969, 30, 104-l 14. Salzberg, P. M., Parks, T. E., Kroll, N. E. A., & Parkinson, S. R. Retroactive effects of phonemic similarity on short-term recall of visual and auditory stimuli. Journal of Experimental Psychology, 1971, 91, 43-46. Scarborough, D. L. Memory for brief visual displays of symbols. Cognitive Psychology, 1972, 3, 408-429. Slosson, R. L. Slosson Intelligence Test. New York: Slosson Educational Publication, Inc., 1963. Sperling, G. The information available in brief visual presentations. Psychological Monographs, 1960, 74(11), Whole No. 498. RECEIVED:

November

27, 1978; REVISED:

October 3, 1979.