JOURNAL

OF EXPERlMENlAL

CHI1.D

PSYCHOLOGY

51,

30-57

(1Y’)l)

Enhancement of 4-Year-Old Children’s Memory Span for Phonologically Similar and Dissimilar Word Lists NELSON

J.

COWAN,

SC-OTT

AND

Previous

research

suggests

that stimulus list repetitions for the products of rehearsal.

that

SAULTS,

MOLLY

CARRIE

preschool

children

can improve However,

dissimilar be made

Cumulative span and more serial

the

insight order

items mnre

repetition phonological into types information)

dren attempting to recall discussed. c 1441 Acadcmtc

found similarity

to cause effect.

spoken Prc\\

lists.

The

if the overall obtained

a moderate Other types

of stimulus redundancy or not helpful (e.g..

deficient

presumably research

in rehearsal

and

hy \uhstituting included interitem

or more. We examined the utility span task in which spoken words Lists with phonologically similar

were included. to determine similar to what 15 ordinarily was

are

their recall. the previous

or postlist retention intervals of several seconds of list repetitions with reference to an ordinary were presented I s apart for immediate recall. versus could

WINTEROWD.

SHERK

pattern in older

increase in hoth of list repetition

that forced

were helpful articulatory

underlying

mnemonic

(e.g., coding)

of recall children. memory provided repeated to chil-

processes

arc

lnc

One of the best-established findings in the development of memory is that verbal memory span. the number of sequentially presented. unconnected spoken items that a subject can repeat. increases with age. Although the mechanisms underlying this developmental change remain unclear (Dempster, 1981), one potential contributing factor is the covert rehearsal of list items. Children use verbal rehearsal more as they increase in age (Flavell. Beach. & Chinsky. 1966), and rehearsal methods become more cumulative and effective throughout the elementary school years (Naus. Omstein. & Aivano. 1977). Moreover. training subjects to rehearse when they are in a transitional stage (typically, kindergarten or first grade) This project was supported by National Institutes of Health Grant 2-K23-~LD2133X awarded to the first author. WC thank Cristy Cartwright. Judy Huchman. Jill Masher. and Paige Meinhart for their assistance in data collection. Correspondence and reprint requests should he addressed to Nelson Cowan. Department of Psychology, 3111 McAlester Hall, University of Missouri. Columbia. MO 6521 I.

PRESCHOOL

CHILDREN’S

MEMORY

SPAN

31

can dramatically improve their memory performance (Keeney, Cannizzo, & Flavell, 1967; Kingsley & Hagen, 1969). Nevertheless, as Huttenlocher and Burke (1976) pointed out, there is insufficient evidence to link the development of memory sp~rz as it is ordinarily measured (e.g., with items about 1 s apart. using an immediate, verbal response) to the development of rehearsal processes. The devclopmental evidence for the importance of rehearsal has focused on rehearsal of items during a forced, postlist delay (e.g., Keeney et al., 1967) and during extended interitem delays of several seconds (e.g.. Hayes & Rosner, 1975; Naus et al., 1977), but not during an ordinary span task. The present article helps to fill this gap in our knowledge with experiments. using 4-year-old children as subjects. in which the span task was modified to provide several types of redundant speech information that might serve as substitutes for rehearsal. One type of evidence suggesting that some sort of covert verbal process is important in memory span is the marked developmental increase in effects of the phonological similarity between items on a list (Conrad. 1971; Hulme, 1984). Previous research (e.g., Conrad, 1964) had indicated that adults’ serial memory of a set of printed items to be recalled was impaired if the items’ labels sounded similar to one another, an effect that we will refer to as the “phonological similarity effect” (PSE). Conrad (1971) examined the development of the PSE using pictures of eight items with names that sounded similar (caf, VUUZ, tnur, etc.) and eight that sounded dissimilar (fish, hmd, spoon, etc.). The memory advantage for items with dissimilar names was found to increase from the youngest (35 years) to the oldest (8-11 years) age group. This development of the PSE may be useful in understanding why memory span develops, inasmuch as it offers a condition (specifically. phonological similarity between the names of memory items) in which the developmental increase in span is markedly attenuated. In Conrad’s (1971) experiment, each picture was named by the cxperimenter as it was presented, and Hulme (1984) replicated the effect using the names only, without the pictures. Therefore. the development of the PSE cannot be attributed solely to an increase in the ability to verbally encode pictures. The increasing sophistication of some other form of speech processing such as covert rehearsal could account for the development of the PSE and, at least in part, for the development of memory span. In one adult study supporting this notion, Cowan, Cartwright, Winterowd, and Sherk (1987) presented spoken lists of phonologically similar or dissimilar items to be recalled. sometimes with a concurrent articulatory suppression (rehearsal-blocking) task in which subjects whispered letters of the alphabet. Performance was found to be impaired by articulatory suppression to such a great extent that it was very similar to what Hulme (1984) obtained for S-year-old ehildrcn, both in the overall span and in

32

COWAN

El‘

Al..

the magnitude of the PSE. Moreover, various investigators have found that memory span is correlated with speaking rate, both in adults (Baddeley, Thomson. & Buchanan, 1975: Case. Kurland, bi Goldberg. 1983) and in children of various ages (Hulme. Thomson. Muir, Cut Lawrence, 1984: Hulme & Tordoff. 1989). These correlations arc presumed to occur because subjects who can speak more quickly can cngagc in more efficient covert rehearsal. Ultimately. though, the causal basis of developmental changes in memory span cannot be proven by correlations between factors in children or manipulations in adults. Correlations could arise because both factors arc affected by some third factor. and manipulations in adults may not act upon the same factors that arc important developmentally. A more direct type of evidence of the direction of causation would be a demonstration that training of a particular verbal factor in children improves span. Unfortunately. attempts to increase span through training have encountered important methodological difficulties. Hulme and Muir (19XS) tried to improve memory span in 7-year-old children by training them to increase the rate of articulation of the particular words to be used in the memory sets. but it proved to be impossible to increase articulatory rates very much. even after extensive training. Consequently. the evidcncc neither supported nor disconfirmed the causal relationship under examination. If the PSE wcrc to bc examined in a training study. ;I further methodological difficulty might well be encountered. Specifically, at the young ages at which the PSE is much smaller than in adults (up to about 5 years of age; see Conrad. 1971 and Hulme, 10X4), verbal memory span improvement may be difficult or impossible to achieve through rehearsal training.’ If using verbal training to increase young children’s memory span and PSE is not practical, the next best approach may be to provide children with repetitions in the stimuli mimicking types of verbal redundancy that rehearsal presumably would produce for older subjects. This is the approach that Hayes and Rosner (1074) took. The usefulness of the approach is supported by the general tinding that the mnemonic value of rxperimenter-generated item repetitions is at lcast as great as repetitions generated by the subject (Ornstein CyrNaus, 197X). The Hayes and Rosner (1975) procedure with S-year-old children was ’ In an unpublished children to cumulativelv to repeat the entire moderately successful not raise performance the attention4 prcat (cf. memoriration.

htudk with 37 -I-year-oldx and 37 5-year-olds. we attempted to trnln rehearse a spoken lkt. In the cxperimcntal condition. subjects were current list after thu presentation of each item. Even though we were in training children to carry out this tash. cumulative rehcarsd did ahove what was obtained in an ordinary span task. WC suspect that

demands Guttcntag.

of carryins 19X4) that

out cumulative subjects wc’rc‘

rehcatxd distracted

at these young ages from the primary

wc’rc task

VI 01

PRESCHOOL

CHILDREN’S

MEMORY

SPAN

33

similar to that of Conrad (1971), except that three different groups of subjects received different types of stimulus redundancy. As in Conrad’s procedure, the stimuli used by Hayes and Rosner were sequences of labeled pictures, which were concealed after their presentation. Their subjects were to indicate recall by pairing the hidden pictures with a duplicate set that was made available only after the last list item was presented. Subjects in all groups were to name each picture when it was presented, but the groups differed in the procedure at the time of recall. In the control group, there was no verbalization at recall. In the “verbal labeling” group, subjects were required to label each concealed picture just before finding its match in the response set of pictures. Finally. subjects in the “rehearsal” group were to label all of the pictures, in order, each time a new picture was added to the sequence. Thus, in this condition, verbal rehearsal was cumulative across the sequence. Spans were found to be higher in the rehearsal group than in the other two groups, and a PSE was obtained only in this group. Although the Hayes and Rosncr study nicely demonstrates that some type of verbal process can contribute to memorization, several aspects of the procedure make the generalizability of the findings to ordinary memory span uncertain. First, items to be recalled were introduced 5 s apart. Second, subjects were to repeat each item at the time of its presentation in all conditions. Third, a picture-matching response was used rather than the typical spoken response. Below, we summarize the possible consequences of these departures from the typical span task, which we will reexamine in our research. Hayes and Rosner introduced items 5 s apart in all conditions, but in the cumulative condition, repetitions of earlier items were interposed within the 5-s periods. Cumulative repetition therefore might have been useful simply because it spanned the relatively long delays bctwecn items. Consequently, this study is most appropriately grouped with the previous demonstrations of the value of cumulative rehearsal during a delay (e.g., Keency et al.. 1967: Naus et al., 1977) rather than with the typical memory span tasks. It is also worth noting that the PSE has been obtained within 5-year-olds in previous studies (e.g., Conrad, 1971: Hulme. 1984; Hulme 6r Tordoff, 1989), so that the complete absence of such an effect in the control and verbal labeling groups of Hayes and Rosner suggests that the test situation was not equivalent to a span task. One goal of the first experiment within the present study was to re-examine the stimulus repetition effects obtained by Hayes and Rosncr with a more typical, l-s delay between items in the control tests of memory span. Ail subjects in the Hayes and Rosner (1975) study were to label the items as these were presented. This was reasonable within the context of their study. because they were not focusing on developmental changes in picture-labcling. However, the effect of a labeling rcquircment for au-

34

COWAN

ET AL

ditory stimuli is unknown, and potentially very important for an understanding of covert verbal processing. In adults, there is evidence that there are distinct acoustic and articulatory (speech-motor) codes that arc used independently in recall (e.g., see Cheng, lY74). It is unclear which of these codes is important in memory span or the PSE. If young children did not spontaneously form an articulatory code. that might account for their reduced span and PSE. Accordingly. a second goal of our study (in Experiments 2 and 4) was to examine effects of the articulatory coding of acoustic stimuli. Finally. like Conrad (1971). Hayes and Rosner (lY75) used a picturematching response instead of the spoken response that is required in an ordinary span task. The response mode may affect the types of coding that children use. For example. in a study of the PSE in 4- to S-year-old children (Brown, lY77a) using lists of printed letters followed by either printed or spoken test probes that wet-c to be assigned to the correct serial positions, the PSE was obtained for spoken probes only. Further. several studies (Brown. lY77b; Hayes B Schulze, 1077: Hitch, Halliday. Schaafstal, & Schraagen, fYX8) have found that young children have a preference toward visual coding when it is applicable. The result could be that young children carry out less verbal processing when the response mode is visual. Thus, although Hayes and Rosncr found that the cumulative repetition of spoken words was useful in a pictorial-response situation, it is unclear if this would bc true if a spoken response wcrc required. That is the response mode used in all four experiments within the present study. A final goal of the study was to examine the role of serial order in formation in memory span and the PSE. Rcscarch with adults (Baddelcy, 1086; Wickelgren. lY65) suggests that the PSE occurs primarily because of the lack of order information for phonologically similar items. and there is also research with -l-year-old children (Locke. lY71) from which similar conclusions can be drawn. The role of serial order information was examined in Experiments 3 and 4 of the present study. In summary, four experiments were conducted with 4year-old children. who are at the lower end of the range at which the PSE has been examined, in order to examine whether or not memory span and the PSE would be enhanced by three different types of auditory presentation redundancy: (1) cumulative repetition of the lists. (2) required articulatory coding of auditory stimuli, and (3) independent cues to the sequential order of items. EXPERIMENT

1

This experiment was conducted in order to determine if cumulative repetitions, which presumably mimic the cumulative rehearsal that 4-yearolds cannot do, would assist in serial recall and/or increase the magnitude of the PSE in a typical verbal memory span task. The control conditions

PRESCHOOL

CHILDREN’S

MEMORY

SPAN

35

were close replications of Hulme (1984). However, in the other conditions, lists were presented cumulatively. For example, a trial might begin with the presentation of the word fish; assuming that the subject repeated this word correctly, the list fish, hand might then be presented; then fish, hand, spoon; and so on, until the subject was unable to correctly repeat the sequence that had accumulated. The rate of presentation was 1 item per second in all conditions. Of course, this meant that the time between the introduction of new list items in the cumulative presentation conditions was longer than in the control conditions and increased as the list cumulatively progressed. The rationale was that, given the apparent impossibility of training children to increase their rate of rehearsal substantially (Hulme & Muir, 1985), the verbal products corresponding to a rapid rate of rehearsal would be artificially provided in the cumulative conditions, over the longer time period that is necessary for young children. Method Subjects. The subjects in the final sample were 32 children (17 male, 15 female) from lower-to-upper middle class families living in or near Columbia, Missouri. The mean age at the time of testing was 48.72 months, SD = 0.63. Names and addressesof the subjects were obtained originally from birth announcements in the local newspapers. and parents were sent letters followed by telephone calls. An additional child was eliminated from the sample because of an experimenter error. and six more were excluded because they failed to follow instructions (e.g.. spoke during stimulus presentations) or did not complete the session. Material.?. The stimuli were the same spoken words used by Conrad (1971) and by Hulme (1984). The words comprising the phonologically dissimilar set were girl, bus, train, spoon, fish, horse, clock, and hand, and those comprising the similar set were rut, cat, mat, hut, hat, man, hag, and tap. Sets of dissimilar and similar word lists were formed by randomly drawing words from the appropriate set, without replacement for each list. The materials for the control condition always included two dissimilar and two similar lists of each list length from 2 to 8 items, arranged by list length. For the experimental condition, the materials simply included two dissimilar and two similar lists of 8 items each. to be presented cumulatively. Procedure. Children were tested individually in a quiet room. All words were read aloud by the experimenter with a list intonation. The child first was asked to repeat all 16 of the test words, in a random order, to ensure that they were familiar with these words. Next, they were told that they were going to be asked to remember some words and say them $ack. They were tested on two 3-word practice lists (foot, knife, cow, 2nd hrrci-, sun, &US) until these lists could be repeated successfully. Then. testing

36

COWAN

ET AL

on the dissimilar and similar lists in one condition (experimental or control) began, with a l-s presentation rate. Half of the subjects received all control trials first, and half received all cumulative repetition trials first. The presentation within either of these two conditions alternated between dissimilar and similar lists. Half of each group began each condition with a dissimilar list. whereas half began with a similar list. There were two different randomizations of words for both the control and the experimental conditions, and all four possible combinations of these randomizations were used equally often across subjects. In the control condition, testing began with a 2-word list and continued, alternating between list types, until the subject made an error in the repetition of both lists of a particular word type of a particular length. The child’s span on that type of list was defined as the length of the longest list that was repeated successfully on at least one of the two trials, with credit given only if the serial order of words was correctly maintained. When the criterion level was reached for one type of list, testing on the other type of list continued alone until its criterion level was reached also. In the experimental condition, a span estimate was derived consecutively from each of four lists (2 dissimilar and 2 similar) of 8 items each. Within each list, Item 1 was first pronounced. and the subject was to rcpcat it; if the subject was successful, Items l-2 were then pronounced; and so on, cumulatively increasing the presentation length until the subject made an error. The list type alternated, and a subject’s span for a particular list type was defined as the longer of the two span estimates dcrivcd from that list type. Subjects received a line drawing with spaces for colored stickers, which they received at designated times regardless of their performance. as a reward for their continued participation.

Memory spans were analyzed in a 2 x 2 analysis of variance with the degree of phonological similarity of list items (dissimilar vs similar) and the list presentation condition (control vs cumulative) as within-subject factors. The cell means in this experiment are shown in Table I. The effect of phonological similarity (the PSE) was highly significant, F( 1. 31) = 52.90. p < ,001. In agreement with Hayes and Rosner (1975), cumulative repetition of the list was found to assist recall, F( 1, 31) = 29.99. p < .()()I. However, the interaction of Phonological Similarity x Presentation Condition was only marginally significant, F( 1, 31) = 3.29, I> < .0X. In planned comparisons within presentation conditions. it was found that the PSE was highly significant in both the control condition. E’( I. 31) = 13.62. p < .()()I. and the cumulative repetition condition, F( 1. 31) = 40.49, p < .OOl. This finding is in agreement with Hulmc and Tordoff

PRESCHOOL

CHILDREN’S TABLE

MEAN

MEMORY

SPAN FOR EAcw

MEMORY 1

CONDIWN

IN EYP~RIM~N~

Presentation Type

of word

list

Control

Similar

1

--

conditions (‘umulairw

3.41

Dissimilar

37

SPAN

presentation 1. IY

(3.5X) 7.X-l

(4.31) 3 3,

(3.00)

(3.31)

NOP.

Means

ccmdition

are

acrnss

26 subjects

who

;Itt;iined

a memory

span

of at lea&t

1 in :I( least

one

in parentheses.

(19X9). Conrad (1971) found no PSE in 4-year-olds, but this discrepancy could have occurred because he used a picture-matching response. The fact that cumulative presentation enhanced children’s recall relative to a control test of word span establishes the generality of this finding, which was obtained first by Hayes and Rosner (1975) under very different test conditions. It could have been argued that childrens’ performance in the control condition within their study was impaired by the long (5-s) interitem period or the picture-matching response. but cumulative prcsentation was of use to children also in the present study. in which the interitem delay was 1 s and a spoken response was elicited. Further. as a practical note, cumulative presentation now can be recommended when one wants a young child to learn an arbitrary item sequence (e.g.. a telephone number). The meaning of the marginally significant interaction of Phonological Similarity x Presentation Condition should he considered carefully. Inasmuch as Hayes and Rosner (1975) obtained a significant interaction of these variables under slightly different conditions. one must be concerned about the possibility of making either a Type I or a Type 11 error in the present case. Upon inspecting the individual subject means, it appeared that some subjects may have been functioning too poorly or erratically in the task to benefit from additional stimulus redundancy in the cumulative condition. To investigate this possibility statistically, we conducted another analysis that included only those subjects who achieved a span of 4 or higher in at least one of the four conditions of the experiment (n = 26). The mean spans for these subjects are shown in parentheses within Table 1. For these subjects there were not only significant effects of Phonological Similarity, F( 1,25) = 58.78. p < .OOl. and Presentation Condition, F(1, 25) = 24.24, p < .OOl, as in the full subject sample; there was also a significant interaction of these variables. F( I. 25) = 6.45, p < .02. Across the 6 subjects who were excluded from the above analysis, the

38

COWAN

ET Al

mean for the control-dissimilar trials was 2.67 (SD = 0.52); for the controsimilar trials, 3.17 (SD = 0.41); and for both the cumulative-dissimilar and cumulative-similar trials , 2.83 (both SD’s = 0.41). These children and their parents tended to appear a bit more anxious than most about the test situation. These children also may have had some difficulty in maintaining attention to the task in the cumulative presentation condition, given that several of them looked away at the points at which their spans were exceeded. Otherwise. they seemed to learn and perform the tasks in much the same way as the children who achieved higher memory spans. Given that Hayes and Rosner (1975) used subjects who were a year older than subjects in the present study. the most prudent conclusion is that the present results arc consistent with those of Hayes and Rosner. Their findings can no longer reasonably be attributed to the differences between their method and an ordinary memory span task. Both studies suggest that at least part of the effect of cumulative presentation is to strengthen a speech-based code that is useful in recall. especially when the items on the list have dissimilar names. However, cumulative presentation may reinforce this speech-based code substantially only in subjects who have reached a certain minimal level of ability in the memory span task. The performance levels of our subgroup of 4-year-olds for whom ;I Phonological Similarity x Presentation Condition interaction was obtained (Table 1, in parentheses) is most similar in memory span to the S-year-old group of Hulmc (1984). rather than his 4-year-old group. With the assistance of cumulative presentation. their pattern of performance became more similar to Hulmc’s &year-old group. EXPERIMENT

2

Is is actually the cumulative nature of the presentation that was beneficial for recall in the first experiment? Another possibility is that the cumulative presentation was effective only hecausc it rcquircd that subjects pronounce the words. This would be important if young children do not immediately and automatically form an articulatory code for an auditory stimulus (i.e.. do not activate the neural circuits that will be needed for verbal repetition of the list items). If this result were obtained. it would imply that cumulative presentation was effective for different rcasons in the present Experiment I versus the Hayes and Rosner study, inasmuch as Hayes and Rosner required articulation of the items in every condition and did not use a verbal memory response. To investigate the articulatory coding hypothesis in the present cxperiment. subjects were to repeat each item in the experimental condition as soon as it was presented. and then they were to repeat the cntirc list from memory. In the control condition. however, they were to listen quietly to each list of words and then repeat it. exactly as in the control

PRESCHOOL

CHILDREN’S

MEMORY

SPAN

39

condition of Experiment 1. If the formation of an articulatory code is critical, the pattern of data should resemble that of Experiment 1. On the other hand, if 4-year-old children automatically form an articulatory code, then the repetition of each word in the list should be of little mnemonic value. In fact, by breaking up the auditory presentation, these repetitions actually could be detrimental to recall.

Method Subjects. The subjects

were 16 children (6 boys and 10 girls. all 49 months old) who were recruited in the same manner as children in Experiment 1 but did not participate in that experiment. One additional child failed to complete the study. Materials and design. The materials were a subset of those used in Experiment 1. The two sets of word lists from the control condition of that experiment were used for both conditions of the present experiment. Half of the subjects received Stimulus Set 1 for the control condition and Stimulus Set 2 for the repetition condition. whereas the assignment of stimulus sets to conditions was reversed for the remaining subjects. Procedure. The procedure in the control condition was the same as in Experiment 1. In each trial within the experimental condition. however, the subject was to repeat each item as soon as it was presented, and then the subject was to repeat the entire list when it ended. Whereas in Experiment 1 the task was the same from the subject’s point of view in both conditions, that was not the case in the present experiment. Therefore, it was necessary to carefully train the subject before each condition. The experimenter used hand signals in both conditions, to make sure that the child always knew if the list was ongoing (outstretched hand with palm down) or completed (palm up). For the repetition condition. subjects were told the following: “I am going to say some words. After I say each word, I want you to say it back to me. When I turn my hand over (from palm down to palm up) that means I want you to tell me al1 of the words that we said.” During the first practice trial. a second experimenter modeled the task by responding along with the subject. The experimenter who presented the list waited until the last word was repeated before giving the signal for the subject to recite the entire list. The first test trial was not begun until the subject demonstrated an adequate understanding of the task in the practice trials. Presentation and list conditions were counterbalanced as in Experiment 1, with similar and dissimilar lists presented in the same alternating order within a subject’s control and repetition conditions. All aspects of the experiment except those mentioned above were the same as in Experiment 1.

40

COWAN

ET

AI

The ANOVA was analogous to that of Experiment 1. except that the experimental presentation condition was repetition of each item by the subject, rather than cumulative presentation. The mean memory spans for each condition arc shown in Table 3. As in Experiment 1, there was a large effect of phonological similarity. F( 1. IS) = 30.11. p c ,001. There was also ;I very consistent effect of the presentation condition, F( 1. 15) = 42.76. 11 < .OOl. Howcvcr, as Table 3 shows, repetition of the words on the list actually lowered memory span relative to the control condition. rather than raising it. The interaction of the two factors in the ANOVA did not approach significance, F( 1. IS) < I. Planned comparisons confirmed that the cffcct of phonological similarity was significant in the control condition, F( 1. 15) = 13.03, 11 c ,005. a\ well as in the repetition condition, E’( I. 15) = 14.88. p x-1 .005. This finding is in agreement with Experiment I. The finding that repetition of each item did not improve pcrformancc suggests that the rcquircd articulatory coding of spoken items was not the feature of cumulative prcscntation that made it helpful to subjects in Experiment 1. There arc several possible reasons why articulatory coding was not helpful. One is that an acoustic/phonetic code may be sufficiently redundant with the articulatory code that the latter was of no value. Alternatively. an articulatorv code may bc of value. but subjects ma) already perform articulatory-coding adequately by the age of 4. The latter interpretation seems prcferahlc because the results of previous studies (Brown. 1977a; Hulme et al.. 1986: Locke, 1971) confirm that 4-year-old children can encode stimuli in an articulatory manner. Within this account, the detrimental effect of repetitions might be explained on the basis that both acoustic and articulatory sources of information are used together, but that there is a tendency of overt repetitions to impede the use of the acoustic source. This could occur because rcpctitions allow more time to elapse between the presentation and recall of the first three list items. or because repetitions break up the acoustic coherence of the list (inasmuch as the auditory stimuli would hc ;I series of words aitcrnating between the experimenter‘s voice and the subject’s

PRESCHOOL

CHILDREN’S

MEMORY

SPAN

41

voice). Similar factors appear to have influenced the use of acoustic memory in many studies with adult subjects (Cowan, 1984). EXPERIMENT 3 When items are presented repetitively, as with cumulative presentation, both the items on the list and their serial order arc repeated, so it is not clear what is the important aspect of the repeated presentation. However, previous research with adults (Baddeley, 1986; Wickelgren, 1965) and children (Locke, 1971) has indicated that the poorer recall of phonologically similar lists is attributable primarily to the difficulty of recalling the correct serial order of items in those lists. rather than to item recall. Accordingly, our third experiment was designed to examine the contribution of redundant order information in children’s recall. It included two conditions that were equated for item information but differed in the amount of serial order information that they provided. In one condition. the word list was repeated three times before the subject was to recall it. providing multiple presentations of the items and their sequential associations. In the other condition, each word was repeated three times in a row. providing multiple presentations of the items but only a single prcscntation of the serial order. This manipulation may differ from cumulative presentation (or cumulative rehearsal, for that matter) in the relative amounts of order information provided for dissimilar versus similar lists. Cumulative presentation provides repetitions only so long as the subject continues to recall the accumulated list correctly. because the presentation ends when the subject errs. That method provides more repetitions of serial order information (as well as item information) for dissimilar lists than for similar lists. Likewise, when an older subject rehearses cumulatively, reactivation of the correct sequence in memory ends if and when the subject introduces an error into the rehearsed sequence or cannot keep up with the list, and this should provide more repetitions for dissimilar lists. In contrast to these situations. the present manipulation provides an equal amount of order information for both the dissimilar and similar lists. because no response is elicited until the entire repeated presentation is completed. Thus. if the number of repeated presentations is important for retention of serial order information. then the list-repetition and word-repetition conditions of the present experiment should differ in the level of recall. but not in the magnitude of the PSE. On the other hand, a difference in the PSEs for the two presentation conditions should be obtained if rcdundant order information simply cannot be used well for similar lists. Method Sltbjects. The subjects were 32 children (17 male. 15 male, mean age = 52.13 months, SD = 1.54) who were recruited as in the previous

42

COWAN

El’ AI

experiments but did not participate in those experiments. An additional child failed to complete the session. Materiuls NH~ ~es@r. The printed materials wcrc identical to those of Experiment 3. Procedure. Because of the potential difficulty of following directions in this study (given that subjects wcrc to repeat each list item only once. regardless of how the lists wcrc presented), the task was first modeled in the practice phase. with one of two experimenters acting as the subject. Then the trial was repeated with both the model and the child answering together and. finally, the child attempted each practice trial unassisted. This procedure usually helped the subject to understand the task within a few trials. In the word-repetition condition. each word in the list was repeated three times in a row. whereas in the list-repetition condition, the entire list was repeated three times in a row. There was also an important between-subject variable. Specifically. half of the subjects received a final, extra repetition of the list as a whole. following the three repetitions of either the words or the list. There was a pause of about 1 s between the three repetitions and this extra list repetition. For the other half of the subjects, there was no extra list repetition in either condition. A sample sequence for a dissimilar. word-repetition trial (with 3 items) is as follows: All subjects: fish, fish, ,fish; sport, .spoot~~ spoon; I~md, hnd, hund; Extra-list-repetition Group only: l-s pause. then fislr, S~NOW, Irand; All subjects: recall. (Correct response: “fish. spoon. hand.“) For a list-repetition trial. on the other hand. the sample sequence would be as follows: All subjects: fish, .spoo~, hnd; jish, spoot~. hnnti; ,jish, ,syoon. hmd; Extra-list-repetition Group only: l-s pause. then fish, .spoon, hmd; All subjects: recall. (Correct response: “fish. spoon. hand.“) The between-subject factor of extra list repetition was added in order to distinguish between the possible benefit of multiple list repetitions on the memory representation versus the possible tendency of at least one list repetition to east task demands. Specifically, with word repetitions only. the subject would have to mentally compose the appropriate response by collapsing across stimulus repetitions of each word. rather than simply repeating a stimulus sequence verbatim. Counterbalancing of the two within-subject conditions (word versus list repetition) was entirely analogous to Experiment 2. The entire withinsubject counterbalancing scheme was replicated for the two subject groups (i.e.. subjects who did or did not receive a final, extra list repetition on each trial ).

PRESCHOOL

CHILDREN’S

MEMORY

TABLE

MEAN

MEMORY

3

SPAN FOR EACH GROUP IN EACH CONDITION Type

Type

of word

list

Words Group

1: Recall

of

after

List three

Group Dissimilar Similar

2: An

extra

3.44 7.x1

3

repeated

repetitions

2.56 1.19 list rcpctition

IN EXPERIMENT

x 3 repetition

repeated

immediately

Dissimilar Similar

43

SPAN

3.00 3.31 before

recall 3.50 3.IY

Results and Discussion The data were analyzed with a 3 x 2 x 2 design with Phonological Similarity (similar/dissimilar) and the Manner of Repetition (words versus list repeated 3 times) as within-subject factors, and with the presence versus absence of an extra list repetition as a between-subject factor. The results are shown in Table 3. Once again. there was an overall effect of phonological similarity across presentation conditions, F( 1. 30) = 22.03, p < ,001. There was also a large effect of the manner of repetition, F(1,30) = 83.48, p < ,001. As shown in the table, performance levels were higher overall with list repetition than with word repetition. However, the interaction of Phonological Similarity x Manner of Repetition did not approach significance, F( 1, 30) < 1. From these results, it is clear that repetition of the sequential associations between items is helpful in recall, but it is about equally helpful for lists of similar versus dissimilar items. There was no main effect of the between-subject factor (presence or absence of an extra list repetition on each trial). but it did interact with the manner of repetition, F( 1, 30) = 41.88, p < .OOl. As Table 3 shows, the basis of this interaction is that the separation between the word- and list-repetition conditions was much smaller for the subjects who received the final, extra list repetition. Despite this interaction, however, separate ANOVAs for the two groups of subjects both produced the same main effects of phonological similarity and of the manner of repetition as in the overall analysis (all p’s < .OS). No other effects of any of the ANOVAs were significant. The finding of a list-repetition advantage over word-repetition, even for subjects who received an extra list repetition on trials of both types, implies that the difference between list- versus word-repetition resulted at least partly from the benefits of list repetitions on subjects’ memory representations, rather than from task demands. Planned comparisons indicated that the PSE was significant for the

44

COWAN

El‘

At..

subjects in the extra-list-repetition group, F( 1, 30) = X.98, p < .Ol, and in the no-extra-repetition group. F(1, 30) = 11.54, p < .005. Across groups, it was significant in the word-repetition condition, E‘(1, 30) = 10.23. p < .OOS, and in the list-repetition condition, F( 1, 30) = 10.21, p < .005. The absence of any interaction of the between- or within-subject presentation factors with the phonological similarity factor implies that the serial order information provided by the list-repetition technique was of approximately equal benefit for both similarity conditions. Following the logic offered earlier. this result further suggests that children can make use of redundant serial order information for the recall of phonologically similar. as well as dissimilar. lists. The repeated list presentation method of the present experiment apparently eliminated the difference in the amounts of rcpctition that would occur for similar versus dissimilar lists in a cumulative presentation or cumulative rehearsal situation. Although the list-repetition condition of the present experiment appears to have circumvented the ordinary problems of cumulative rehearsal by always providing rcpcated exposure to the correct sequence, it may still be inferior to cumulative rehearsal as a mnemonic aid. bccausc cumulative rehearsal permits the subject to practice repeating the list in l-word increments as it progresses. This factor may explain why. for dissimilar lists. the overall benefit of cumulative presentation (in Experiment I) was greater than the benefit of list repetition (in the prcscnt experiment). EXPERIMENT

4

There were several purposes of this final experiment. First. WC wished to determine if subjects could benetit from nonverbal cues to serial order information. or if the benefit accrued only from verbal sources of order information. One reason to cxpcct that order information could be used only when presented in a verbal mode is that several recent theories of the auditory modality superiority in adults’ recall have posited that the auditory modality is better suited than vision for retaining temporal information (Glenberg. Mann, Altman, Forman, & Precise, 1989; Penney. 1989). On the other hand, the visual modality might be used to convey sequential information by mapping the temporal sequence onto a visual spatial sequence that children can recode verbally. From the point of view of Paivio (1986, Chapter 8). it is the subject’s internal coding modality rather than the stimulus modality that accounts for the spatial versus sequential difference. with verbal coding best suited to serial recall rcgardless of the stimulus modality. In order to investigate the role of a nonverbal cut to order information, pictures of the words were used in the present experiment. unlike the previous ones. For half of the subjects, the pictures were placed in a horizontal row as they were presented, thus providing access to the serial

PRESCHOOL

CHILDREN’S

MEMORY

SPAN

45

order of items during the entire list presentation. For the other half of the subjects, the pictures were placed on top of one another, providing no order cue other than the most recent item. A second purpose of this experiment was to reexamine the PSE in the presence of a set of pictures. Conrad (1971) proposed that no PSE in 4year-olds was obtained within his experiment because young children relied upon pictorial information when it was available rather than using the associated verbal codes (cf. Brown, 1977b; Hayes & Schulze, 1977: Hitch et al., 1988). If 4-year-olds rely primarily on picture codes when these are available, even when the response mode is verbal, then the PSE that was obtained in the lirst three experiments of the present study should vanish in this last experiment. A third purpose of this experiment was to reexamine the role of articulatory coding, this time in the presence of a set of pictures. A possible account of the reliance of young children on pictorial information is that these children do not automatically convert the auditory component of a multimodal stimulus to an articulatory form. In order to investigate this possibility, the pictures were named by the experimenter on half of the trials and by the subject on the other half of the trials. If subjects are capable of using an articulatory code but do not form one automatically, and if the presence or absence of that code determines whether a PSE will be obtained in the presence of visual information, then the effect of phonological similarity should be larger when the subjects arc to name the pictures themselves, thus forming an articulatory code. Conrad (1977) obtained such an effect, but the procedure of that study involved a picturcmatching response, which might have discouraged self-initiated articulatory coding.

Subjects. The subjects were 31 children (20 male, I:! female. mean age = 57.19 months, SL) = 1.91) who were rccruitcd as in the previous experiments but did not participate in those experiments. Two additional subjects failed to complete the study. and one additional subject was excluded from the sample because of experimenter error. Materids. In addition to the sets of lists used in the last two experiments, a set of line drawings was constructed to illustrate each word on each list. including the practice words. Each line drawing was presented on a white, laminated, 7.5 cm x 8.0 cm card. Procedure. Subjects were assignedrandomly to four groups that differed on two factors in combination. For half of the subjects (Row Groups), picture cards were to be spread out in a row from left to right on each memory trial, with each card added to the row just before its name was pronounced. For the other half of the subjects (Pile Groups), the picture cards were presented one on top of another. Further. for half of the

46

COWAN

El‘

AI

subjects (Listen Groups). the experimenter named the item on each card within the memory trial, whereas the other half of the subjects (Speak Groups) were to name each card in the sequence themselves, using labels learned during the initial picture familiarization period. Based on the two above-mentioned factors in combination, the four groups were the RowListen, Row-Speak. Pile-Listen, and Pile-Speak Groups. Given that there were only 8 subjects in each group, the possibility of group differences in memory ability had to be considered. To check for such differences, each subject was first given a digit span test. so that different groups could be compared under identical testing conditions. No pictures were used in this test. Digit strings were to be repeated in their correct serial order, and the subject was given two chances to correctly repeat a digit sequence of each particular Icngth. The digit span was recorded as the longest sequence repeated correctly. Next. there were word-span practice and item-familiarization phases 01 the experiment. and then the word span determinations for similar and dissimilar lists, with the two types of word lists presented in alternation. All of this was analogous to the previous experiments. The practice trials were conducted using the same procedure that would be used in the test trials. which varied bctwecn groups (see above). However. the initial familiarization with the test word names was standard across groups: the experimenter labeled each picture and the subject was to repeat the name while looking at the picture. Further, for all subjects. all of the picture cards were concealed 1 s after the presentation of the last card in the sequence. Verbal recall was required. without access to the pictures during the recall period. Except for the changes mentioned above. the procedure was identical to that of the control condition in Experiments 1 and 2.

The digit span data were submitted to a 7 x 3 ANOVA with the picture arrangement (piled versus spread out) and the source of auditory stimulus (experimenter versus subject) as between-subject variables. The mean digit span was 3.94, and no differences between groups approached significance. Therefore. it seems safe to assume that any effects of sampling variation on group differences in memory span were minimal. The word span data were submitted to a 2 x 2 x 2 ANOVA, with the picture arrangement and the source of auditory stimulus as bctweensubject variables, as in the digit span data, but also with phonological similarity as an additional, within-subject variable. The results are shown in Table 4. Despite the presence of pictures, the effect of phonological similarity was significant once more, F( 1. 3X) = 32.56, p < .()()I. Further, subjects performed better when the pictures were spread out in a row than when they were placed on top of one another. F( 1, 3X) = 6.53. 11

PRESCHOOL

MEAN

DISSIMILAR

AND SIMILAR

CHILDREN’S

MEMORY

TABLE 4 LISI SPANS FOR FOUR TREATMEN.I. Type

Treatment Row-Listen Row-Speak Pile-Listen Pile-Speak

group

47

SPAN

GROUPS IN EXPERIMENT of word

Dissimilar 4.3 4.13 3.75 3.50

NOW. Key to group designations: Row, pictures spread out in a row: on top of one another; Listen. experimenter labeled pictures in memory subject labeled pictures within memory sequences.

-1

list Similar 3.63 3.3X 3.00 3.13 Pile. pictures piled sequences; Speak.

< .02. However, neither the source of auditory stimulus nor any of the interactions approached significance. These results are totally consistent with the previous experiments. Across experiments it can be said that cues to serial order, whether from verbal or pictorial sources, boosted memory spans both for phonologically similar and for dissimilar lists (Experiments 3 & 4). Moreover. forced articulatory coding had no effect (Experiments 2 & 4). perhaps because 4-year-old children already perform that coding automatically when a spoken word is heard and a spoken response is required. In interpreting Experiment 4, two cautions are in order. First, the number of subjects per cell (8) could have been too small to detect a subtlc effect of articulatory coding. Second, if children can process several items in parallel, it is possible that the effect of the picture presentation method was due to the longer duration of availability of each picture except the last when the pictures were spread out. Nevertheless. in deciding upon a preferred interpretation of the data. it seems most parsimonious to emphasize the similarities among Experiments 2, 3, and 4 as we have done above. Planned comparisons showed that the effect of phonological similarity was significant in the Listen Groups, F(1. 28) = 19.70. y < .OOl. and in the Speak Groups, F( 1, 28) = 13.18, p < .005. It was significant in the Row Groups, F(1, 28) = 28.65, p < .OOl. and in the Pile Groups, F( 1, 28) = 23.44, p < .OOl. The present finding of a phonological similarity effect in 4-year-olds using bimodal stimuli (as Conrad did) is inconsistent with Conrad’s (1971) account in which young children presumably rely on pictorial information when it is available. Perhaps his failure to find an effect in 4-year-olds can be attributed instead to the fact that the response itself was picturematching, whereas a verbal response was required in the present experiment. Young children may tend to rely upon the information that is

already in a form matching the response mode. whereas older children and adults would have a tendency to rely heavily on rehearsable verbal information regardless of the response mode (Conrad. iY64. 197 1). GENERAL

DISCUSSION

The present study strengthens the case. previously argued by several investigators (Baddelcy, 1986; Hulme, Thomson, Muir. W Lawrence. 1984; Hulme & Tordoff, 19X9; Nicholson, 19X1). that the developmental increases in verbal memory span and the magnitude of the PSE between about 4 and 10 years of age can be attributed to an increase in the efficiency of covert verbal rehearsal. Previously. this argument depended on correlations between articulation speed and verbal memory span. rather than on experimental manipulations. Hulmc and Muir (lYH5) were unable to train young children to articulate the words in a set to bc rcmcmbcred more quickly, which would have allowed them to determine if memory span would increase accordingly. Hayes and Rosner (lY75) did dcmonstratc that cumulative repetitions of stimuli increased young children’s serial memory, but they did not examine this in circumstances rcscmbling tests of verbal memory span. The prcscnt Experiment 1 dcmonstratcs that effects of cumulative stimulus repetition also can be obtained within a more typical span task, although the effects were modest in magnitude. A robust finding in all four experiments of the prcscnt study was an effect of phonological similarity on verbal memory span in 4-year-old children, consistent with Hulmc and Tordoff (IYXY). This occurred cvcn when pictures were included in the prcscntation (Experiment 4). in contrast to Conrad (1971). The difference probably can be attributed to the fact that Conrad not only included pictures in the list prcscntation. but also used a picturc-matching response instead of a verbal response. This difference between studies may suggest ;I constraint on the observation (Brown. 1977b; Hayes & Schulzc. lY77; Hitch et al., IYXX) that young children have a preference toward pictorial rather than verbal coding. Actually, young children may USC‘whichcvcr type of code (visual or verbal) best matches the response mode. In contrast, older children and adults often prefer a speech code cvcn for pictorial stimuli, bccausc of the greater mnemonic value of covert verbal rehearsal for thcsc suhjccts. Experiments 2-4 of the present study went on to investigate the value of two types of stimulus redundancy that could have contributed to the effects of cumulative presentation in Experiment 1. First. the fact that the cumulative repetition method required subjects to articulate the items. rather than passively receive them, dots not seem to have been important. Pronouncing each auditory item in a list just after it was presented (in Experiment 7) had a detrimental effect. and labcling each picture rather than hearing it labeled (in Experiment 4) had no effect. The simplest explanation for these tindings is that, although I-year-olds do not cngagc

PRESCHOOL

CHILDREN’S

MEMORY

SPAN

49

in sophisticated rehearsal of spoken items within a list, they do spontaneously articulate the items. There is, in fact. electromyographic evidence of articulatory motor responding during memory list presentations in young children (Garrity. 1975). On the other hand, redundant information about the serial order of list items was potentially an important component of cumulative presentation. Hearing the entire list three times in a row was advantageous over hearing each item three times in a row (in Experiment 3), and it was beneficial to receive pictures spread out in the correct serial order rather than placed in a stack (in Experiment 4). Unlike cumulative presentation. redundant serial order information enhanced recall equally for similar and dissimilar lists. This difference between types of redundancy can be explained with the observation that cumulative presentation (like cumulative rehearsal) provides redundant information only until the subject fails to adequately repeat or rehearse the information, so that it is likely to provide more information for dissimilar lists than for similar lists. In contrast, in our Experiments 3 and 4. redundant information across the list was provided before any response was required. Under these circumstances, children proved to bc able to apply redundant serial order information to both similar and dissimilar lists. The results are consistent with the suggestion (e.g., Hulme & Tordoff, 1989) that the developmental increase in the PSE is caused by the stimulus list repetition that accompanies rehearsal. However, there is still an important issue that must be addressed before a coherent theoretical account of the extant data can be formulated. Specificially, why did 4-year-old children produce a PSE despite their lack of sophistication in rehearsal‘? Several alternative accounts of the PSE can be described clearly within a general model of immediate verbal memory provided by Baddeley (19X6). Within the model, there is an “articulatory loop” that is composed of two components in combination: a passive phonological store that decays at a fixed rate, and an active rehearsal process that can renew the activation of items within the phonological store, provided that subjects can rehearse quickly enough to reactivate items before they decay. One account of the PSE states that it is partly an inherent characteristic of the passive phonological component, which would occur even if there were no rehearsal. According to this account there would probably also have to be another rehearsal-dependent source of the PSE to explain developmental changes in the PSE. A second account states that phonological confusions occur only when the items are refreshed in the rehearsal process. Primarily because the magnitude of the PSE is correlated with the speed of articulation across ages, Hulme and ‘for-doff (1989) favored the latter interpretation, with the assumption that the PSE in 4-year-olds occurs because they have rudimentary rehearsal skills.

50

COWAN

ET Al

However, there is a third possibility that has not been discussed, which would allow the PSE to originate in the active component without implying that 4-year-olds have rudimentary verbal rehearsal skills. Specifically, the process of retrieving items from the phonological buffer to repeat them aloud (which would exist in 4-year-olds) could depend upon mechanisms that also are used to silently retrieve items for covert rehearsal (but only in older subjects). Confusions between similar items within the phonological store would occur during this common retrieval process, with the magnitude of the PSE tied to the total number of retrievals that had occurred by the time of overt recall. and therefore increasing developmentally. In summary. the results of the present study indicate that 4-year-old children’s serial memory for a list of spoken items can be increased somewhat through cumulative presentations that mimic the presumed effects of cumulative rehearsal in older children. Moreover, redundant serial order information appears to he an important component of list repetition. The finding that cumulative repetitions or rehearsals are less useful for similar lists than for dissimilar lists is based on a reduced access to rcpetitions for the similar lists, rather than to an inability to apply redundant serial order information to similar lists. Finally, unlike the usefulness of repeated serial order information, repetition of the items individually was useless or counterproductive. In future research, it will be important to determine if the stimulus redundancy effects obtained here with -I-year-old children actually are comparable to the effects of rehearsal in older children. If so. the effects of stimulus redundancy should be attenuated in children old enough to rehearse. It might also be possible to magnify the PSE through actual rehearsal training in older children. Further. It seems important to determine if there are other sources of the development of memory span in addition to covert verbal processing. In Hulme’s (19X4) data. by IO years of age there appeared to be substantial improvement in span even for phonologically similar lists (which resulted in a general span improvcment between 7 and 10 years with little apparent change in the PSE). It is not clear if covert verbal processing or some other factor accounts for this later development of memory span. Finally. the source of the residual PSE that occurs in 4-year-olds could be explored with a replication of these experiments using even younger children. for whom little or no PSE should be obtained if the PSE is dependent upon at least rudimentary rehearsal skills. REFERENCES Baddelcy. A. D. ( lYN6). Working vwmory. Oxtord. England: Ciarrndon I+\\. BaddeIty. A. D.. & Hull, A. (1970). Prefix and suftix effects: Do they have hasis? .lourr~l of Vo+al Lwrrfin~ uncl Vcrhrrl Hdftrvior. 1X. I ZY- 131).

;I common

PRESCHOOL Baddcley, A. inhibition.

D.. bt Scott. D. Quurteriy Journal

Baddcley.

D.,

A.

Thomson.

of short-term Brown.

R.

memory.

M. (1977a). flexibility.

coding Brown.

R. children.

Case.

R.. Kurland. of short-term

Cheng.

M.

CHILDREN’S

MEMORY

(1Y71). Short-term o.f E.~peritnenral

forgetting P.cycholop,

N..

& Buchanan,

Jourrud

of Verbal

Visual Prrcep/~ul

and phonetic urlcl Mom

(lY77b). An examination Child Develot~mer~t, 48,

R. ( 1964).

Acoustic

of

proactive

length

the

structure

Word

and

Verhul

and

verbal

acoustic and Ps~cholo,~~.

artlculatory 103. 614-61X.

in immediate

memory.

and

Behuvior.

14. 575-589.

children:

Evidcncc

coding

J. (1YXZ). Operational o/’ tuperimermzl Child

of

confusion

(1975).

in the absence 23, 775-283.

memory in preschool Ski1l.s. 45, 1043-1050.

of visual 3X-15.

D. M.. B Goldberg. memory span. Jourrlctl

C. (1974). Different roles memory. Jourrlut of E.yer/merirrd

Conrad.

M. Leurniq

51

SPAN

proccsscs

in preschool

cfticiency f.ywtzo/op,

and 33,

information

Rrrrish

for

the growth 3X6-3OJ.

in short-term

~~J‘I’.\~cJ~oto,~v.

.Jortrtul

55. 75GG. Conrad.

R. (1Y71). The chronology of the r~t~lotImeml P.~~Ch010,~~. 5. 3YX--105.

(‘onrad.

R.

( lY72).

CJ(’ Verhtrl

The

Cowan.

N. (IYXJ).

Cowan.

N..

trrltl

On

Cartwright. children’s

school

dcvclopmental

Lertrtfing

and

C.. speech

J. H.. Beach. D. H.. memory task as a tunction

Garrity,

L.

I. (1Y75).

school

children.

Glcnhcrg.

Mann.

coding

and

Guttentag,

R.

E.

bclopmental D. intlucnce &holog~, Hayes,

D. I‘trild

Hitch, Hulme.

span.

Hulme.

Hulmc,

Rosncr.

S.

in young

L..

mental R.

overt rehearsal 20, 3’)1-3YY.

S.. & Schulze. Derrloprne~zf,

48.

study Forman. effort

(1Y75). and

children.

A. M.. Memory

Silvester. for

J..

Smith.

pictures: Evidence Child P.yycholo,yy,

C.. Thomson. N.. opment of short-term 341-751 I_.

S..

Joltrrttrl

96.

341~3711.

Working similarity

in

C.

memory on serial

A.

of

children:

The

and of

children.

working on memory

memory span: 3. 17S- 1x1. word

length

Joctrrral

(19X4). Speech rate and the E.uperimenral Child P.gddop, development: recall. Journal

The

retention.

Visual

similarity

effects

de-

(‘hi/d

serl,d

In speech rate Psvcholop, in young

A

E.qwrinwrltul

J. M. C. (IYXX).

(1YXh).

coding

rchc.irsal:

of

of acoustic

effect5

Y?-- l(lf~.

preschool

in the effects 650-651.

Muir,

in prc-

Modality

in preschoolers‘

changes Lkvelopmentul

lrcall

in a

17, 373-3X3.

37,

16. 130-137.

for 5pecch 41, 6 1-75.

and

cumulative

Cogrzirion.

qf

rehsar\al

S. (1YXY).

./olrrr~trl

& Schraagen.

of pre-

differcncc~.

Cogt~itiorr.

effect

encoding

Muir, C., & Lawrence, memory span. Journal

C.. Sr Tordoff. V. (19XY). rate. word length. and acoustic t!v~ctlolop, 47, 7’7-87.

of

phonetic

rrrld

&

speech

P.s~c~t~o/o~~v.

instructions.

Visual

[IL,-

I. md