Why Does Memory Span Increase with Age?

Why Does Memory Span Increase with Age? JANELLENHUTTENLOCHER AND DEBORAH BURKE University of Chicago

Ordered recall of auditory digits was obtained from children of 4, 7, 9, and I I years of age. Lists had one of three types of sound pattern: melody, prosody, or monotone. For each sound pattern condition, half the lists were t'emporally grouped. Effects of sound pattern were minor, and not obvio~lslyage-specific. Profound effects of temporal grouping and clear-cut primacy effects appeared for all age groups and all conditions. These results render less plausible the popular hypothesis that the increase of memory span with age is due to the emergence of active strategies. It is suggested that the development of span may be due to an increase in the ease with which children can identify the individual items and encode information about their order.

This paper deals with the development of short-term memory for serially ordered items, in particular, with the auditory digit span.' Ordered item information must be retained for short periods in many tasks; in the processing of linguistic input, in mental arithmetic and other problemsolving activities, as well as in tasks which require straightforward retention, such as remembering a telephone number until it is dialed. Nevertheless, only one aspect of the development of auditory span has been systematically investigated; namely, the size of span at various ages. We lack such basic information as whether the usual bow-shaped serial position curve is found in children's auditory spans, and whether variations in presentation conditions have parallel effects on the spans of children and adults. The major hypotheses which have been proposed to account for the increase in span from two to approximately eight items between 2% and 16 The preparation of this paper was supported in part by Career Development Award 5-K-HD-21,979, and in part by Research Grant HD 03215, both from the National Institutes of Health to the senior author. The authors thank Ulric Neisser for his helpful suggestions on the Results section of the paper. The authors gratefully acknowledge Mr. John Hamble of Siwanoy School. Pelham, NY, Ms. Jeanne Ginsberg of West Orange Playhouse, and Ms. Diane Pinsley of Riverdale Temple Nursery School for their help in obtaining subjects for the study. Requests for reprints should be sent to Janellen Huttenlocher, University of Chicago, Judd Hall. 5835 Kimbark Ave., Chicago, IL. 60637. The term "span" is used here to designate the mean number of items correct in ordered recall of lists of a given length. Sometimes "span" is used to designate n somewhat different measure, namely the list length for which subjects get 50% of the lists completely correct. The two measures are clearly related. and we will use the term "span" because it is more readable than "mean number of items correct in ordered recall" or an abbreviation thereof.

Copyright 0 1976 hy Academic Press. Inc. A l l rights of reproduction in any form reserved

2

HUTTENLOCHER AND BURKE

D E V E L O P M E N T OF M E M O R Y SPAN

years of age attribute it to the emergence of active strategies during childhood. Certain investigators argue that rehearsal plays a role in the development of span (e.g., Flavell. 1970; Belmont & Butterfield, 1969). Others postulate that the ability to impose grouping on a secruence is critical ~ - - - to the increase of span with age. In 1924 ~ a s b ~ l ~sughested ~ a v e that "It is possible that the modal span of four to five obtained from children of the six-year level is the true span, and the higher spans secured from older children and adults are the result merely of grouping or organization, and not a true span" (p. 279). More recently, Olson (1973) and Simon (1974) proposed that age-related increases in span might be explicable in terms of item grouping or "chunking." However, the issue of whether children rehearse or impose organization in attempting to retain auditory sequences has not been investigated. Indeed, we do not even know whether or to what extent children of varying ages can take advantage of experimenterimposed organization in this task. Several points should be made about these developmental strategy hypotheses. The studies used to test them have generally involved tasks quite different from auditory span tasks. Even though children's strategies on some of these tasks do change with age, that does not mean that analogous changes in strategy underlie the development of the span itself. Such an hypothesis can only beevaluated by direct experimental tests with auditory span tasks. Moreover, notions of "strategy" do not constitute overall accounts of short-term ordered recall. As Estes (1972) has noted previously, such an overall account should explain the mechanisms involved in the retention of both item and order information, as well as such phenomena as the ubiquitous bow-shape of the serial position curve, the effects of such variables as grouping, etc. It seems likely that the development of span may derive from age-related changes in these essential operations of identifying items or encoding their order. However, such possibilities have not been explored. Our experiment was designed to evaluate whether developmental r development of span. The possible strategy hypotheses can account f ~the development ofrehearsal strategies was examined, as in earlier studies, by looking for age-related changes in the shape of the serial position curve. The possible development of subject-imposed organization was studied by investigating the effects of temporal grouping and sound-pattern (melody, prosody, or monotone) across age. The hypothesis that the young child fails to impose his own organization on a sequence seems to imply that he should show greater gains from experimenter-imposed organization than an older subject. Of course, children below a certain age might not even notice experimenter-imposed organization, but then these effects should first increase and then decrease with age. In addition, by varying both sound pattern and temporal grouping, we will be able to evaluate the hypothesis that the function of prosody, i.e., normal speech intonation, is to impose grouping (Braine, 1963). ~~

1

3

In addition to these theoretical considerations, the experiment may have practical interest. Informal observation suggests that the presentation of verbal material in a strongly intoned or melodic fashion may enhance its retention by small children. Indeed, teachers of small children frequently speak in a singsong or exaggerated manner, the alphabet is frequently taught via the "Alphabet Song," and children learn commercials and nursery rhymes especially easily. There is evidence that intonation is recognized and produced even during infancy (Kaplan & Kaplan, 1971; Morse, 1972; Gleitman & Shipley, 1971). There is also informal evidence that when small children are first beginning to understand what is said to them, they may be chiefly responsive to strongly intoned input (e.g., Huttenlocher, 1974). Rehearsal and the Serial Position Curve It has been argued that rehearsal can be evaluated by examining the shape of the serial position curve, with primacy providing an index of rehearsal. According to this argument, incoming items are only momentarily available in memory unless they are rehearstd (Atkinson & Shiffrin, 1968; Waugh & Norman, 1965; Glanzer, 1972), and primacy is due to the greater opportunity to rehearse the initial items. Recency, on the other hand, is attributed to the final items being available momentarily after presentation because they are not interfered with by any later items. One of the most convincing pieces of evidence for the rehearsal explanation for primacy comes from a study by Crowder (1969) which uses a variant of the running span procedure. H e found that if sequences of nine items are presented among longer sequences of variable length, rather than among other sequences of nine items, span is reduced and primacy effects are negligible. Indeed, subjects only recall between four and five items under such conditions. Crowder argues that this is because subjects do not rehearse initial items when they have reason to believe that lists will be too long to recall, so that the difference between spans under pt-edictablc and unpredictable conditions indexes the strategic contribution to short-term recall. If this is correct, and if strategy accounts for the development of span, then running spans should be constant across age." Other evidence cited as support for the rehearsal explanation of primacy is that primacy is affected by presentation rate but not by interference tasks, whereas the reverse is true for recency. Since slow presentation Since the present study was completed. Frank and Rabinovitch (Child Dneelopmetlt. 1974,45,397-407)have reported that while span increases for third. fifth. and seventh graders with predictabk conditions ir !evels off for seventh graders with a running span procedure. This leveling off is interesting, but the fact that running span increased bct\veen third and fifth grade suggests that. ; ~ tleast in part, the development of span is r ~ o f ~.cl;ltedro the emergence of strategies. Further studies should be carried out with this proccdurr using younger children. This study also investigated tempor;il grouping and, as in the PI-esent study, failed to find age-related interactions.

HUTTENLOCHER A N D BURKE

permits rehearsal, it should increase primacy. This relation has been found in free recall (Glanzer & Cunitz, 1966), and in probe recall (Ellis & Hope, 1968) but with serial recall, some investigators have found this relation (Jahnke, 1968) and others have not (Posner, 1964). The sensitivity of recency to interference has been demonstrated for all these tasks over a wide range of rates (Glanzer & Cunitz, 1966; Bartz, 1969; Ellis & Eope, 1968). This argument does not satisfactorily explain the bow-shape of the serial position curve. For serial recall, recency requires some explanation in addition to there being a transient store of final items, since these must be retained during recall of earlier portions of the list. Further, the rehearsal explanation for primacy is not satisfactory, since primacy is found even with simultaneous tachistoscopic presentation of items (Harcum, 1967) and with lightning fast auditory presentation rates of six o r 10 digits per second (Yntema, Wozencraft, & Klem, 1964; Aaronson, 1968). Indeed, McCrary and Hunter (1953) report that when errors at each serial position are plotted as a function of total errors, serial position curves for ordered recall are virtually identical under a variety of presentation conditions. According to investigators who assume that primacy is due to rehearsal, lack of primacy in children would indicate that they do not rehearse. In this case, the development of span might be attributable to the appearance of primacy due to the emergence of rehearsal. With free recall, Thurm and Glanzer (1971) found 6-year-olds had greaterprimacy than 5-year-o]ds, and Cole, Frankel, and Sharp (1971) found primacy increased with age for first, third, and eighth grade subjects. However, in free recall, subjects determine the order of output so that differences in primacy simply reflect differences in the order in which subjects say back the items. Indeed, Cole et al. suggest that strategy differences in order of report provide a more likely explanation of the increase in primacy in free recall than does the hypothesis of developmental differences in rehearsal. Furthermore, in a task involving serial recall of visually presented digits, Harris and Burke (1972) found marked primacy, with parallel serial position curves for 7-, 9-, and 11-year-olds. In a well-known series of studies, children were shown pictures which were then turned face down, followed by a probe picture which they were to locate in the series. No primacy was found for nursery subjects by Atkinson, Hansen, and Bernbach (1964), o r by Bernbach (1967). However, other investigators have found primacy in this task with subjects of the same age (Bush & Cohen, 1970; McCarver & Ellis, 1972). Resolution of this inconsistency is provided by Calfee (1969). While his raw data showed no primacy, an analysis which eliminated position bias did show primacy, as did reanalysis of the data of Atkinson et al. The remaining studies which report age-related increases in primacy are those of Hagen (Hagen Kingsky, 1968; Hagen, Meacham, & Mesibov, 1970), and Wagner (1974)

DEVELOPMENT O F MEMORY SPAN

5

the same picture task. Hagen and his colleagues found primacy for all ;\ges and, while there was no statistically significant interaction of serial position and age, the authors argue that an age trend towards increasing can be seen in their graphs. Wagner did find a significant interaction of primacy with age. However, the correction suggested by CaIfee was not used in these studies. ~n summary, the evidence for the role of rehearsal in primacy is mixed. When there is uncertainty about how far beyond span a sequence will be7 simply retain the last four or five items and there is little primacy. This suggests that primacy may require adeliberate attempt to storeitems. On the other hand, primacy occurs with very fast presentation rates suggesting that this attempt, whatever it may consist of, does not necessarily involve rehearsal in the sense of repetition of items. mlich less of repetition. Evidence as to whether primacy increases with age is inconclusive, since only the findings with free recall have avoided measurement problems, and these can be interpreted as deriving from output strategies. Olaonitoljon

The increase of span with age has also been attributed to the development of the ability to organize input, usually described as grouping . (Olson, 1973; Simon, 1974). Experimenter-imposed ~rotlpingis known to be an effective factor in increasing the recall of adults across a wide range of conditions. Effects have been found by having greater time gaps between groups than within groups (Ryan, 1969a; Bower& Winzenz, 1969; Mayzner, Tresselt, Adler, Cohen, & Schoenberg, 1966); by presenting pips between groups (Ryan, 1969a);and by presenting successive groups to different ears (Yntema, Wozencraft, & Klem, 1964). The notion that subject-imposed grouping increases recall is supported by a study which showed that instructing subjects to think of a series as being grouped is also effective a (Wickelgren, 1964). Effects of grouping with auditory presentation have not been studied developmentally. With visual presentation, spatial grouping did not improve serial recall for children aged 7 to 1 I ( S ~ i t z1966; , MacMillan, 1970, 1972; Harris & Burke, 1972), but when digits were both spatially and temporally grouped, their recall did improve (Harris & Burke, 1972). The effects of prosody and melody on Span have not been studied systematically. However, it has been demonstrated that verse rhythms (e.g., trochaic, dactylic) do facilitate the learning of verbal material (Adams, 1915). Since temporal grouping alone facilitates recall. it is not clear whether other components of rhythm are effective. In a study with preschool children, Lahey (1972) found no difference between spans for sequences with or without sentence intonation.

6

DEVELOPMENT O F MEMORY SPAN

HUTTENLOCHER AND BURKE

7

It has been proposed that the effects of grouping might delive from liven though the chunking explanations of grouping which have been rehearsal between groups. This suggests recall would improve with p ~ . ~ p o s eare d unsatisfactory, the development of span might still be increased intervals between groups, which is not the case ( R ~ 1969b), ~ ~ uxplainable , in terms of age-related increases in subject-imposed grouping. Indeed grouping effects occur even with no interval between groups, as 4'h;~tevermechanisms are found to explain the ~ f f e c t sof experimenterwhen groups are demarcated by pips (Ryan, 1969a) o r by dichotic imposed grouping can explain subject-imposed grouping effects as well. I[(,wcver, there are quite different reasons for questioning the subjectpresentation (Yntema et al., 1964). The most popular hypothesis is that experimenter-imposed or subject, irnpoxd grouping explanation of why adults' spans are greater than those imposed grouping increases span by the formation of ~ c - , u n k s , that ~ - is, by of children. It is well established that experimenter-imposed grouping, and lrion,~ 1972; ~ B ~ ~ ir~\tructions ~ ~ to think ~ of , lists as grouped, have large effects on adults. If a redefinition of what constitutes an item ( M ~ & G 1970). Miller (1956) has pointed out that span is limited more in terms of the adults impose their own organization on lists in any case, it is not clear why be of them. manipulations tllrrnber of iterris which can be recalled rather than by the amount of information per item, and that it might be possible for a person to extend his METHOD span by recoding a set of items into a smaller number of more highIy informative items. Since it has proposed that the function of ~ , ~ , , ~ ~h~ variables were temporal grouping and sound pattern There were i~~,, intonation is to impose grouping, it also would presumably chunkinput into sound pattern conditions: prosody, melody, and monotone. Sound pattern was varied a smaller number of units. ;icross subjects so there were three experimental groups at each age level, one for each of the This chunking explanation for the effects of grouping on the recall of rhree sound pattern conditions. Temporalgrouping was varied within subjects so that for each decimal digits is not satisfactory. Miller reports a large increase in span wund pattern condition subjects received half grouped and half ungrou~edlists. several list lengths were used. For each of these list lengths subjects received five grouped and five when a series of binary digits is Octal digits On presentation, and ,,nprouped lists. For the 7 - , 9-, and 11-year-olds, these list lengths were five, six. seven. and then reconverted to binary digits at recall. In this example, subjects knowa For the 4-year-olds, list lengths were four, five, and six. "code" [as Johnson (1970) calls it] for generating the equivalent forms: ".his set list lengths was selected as a compromise among various possibilities. none of 001 = 1, 010 = 2, 01 1 = 3 , 100 = 4, etc. Thus, at least with slow pres. which are perfectly satisfactory. There are various reasons not to use exactly the same set of entation, Such recoding is clearly possible. For decimal digits, it is not list lengths for all the subjects. First, it is well known that ordered recall decreases as list explain the effects of length increases beyond span. Therefore the size of the effects of experimental variables obvious that this recoding notion can, i n depends on the list Iengths used. Since span increases with age, a given list length allows a grouping' The numbers in grouped series are ordered larger improvement from experimental variables for younger children. Furthermore. a set of digits, and thus the groups are not stored as units in long-term memory lists long enough so that the oidest children are not at ceiling would disrupt the Younger c h i l d r e n y ~ nthe other hand. to use different list lengths for each age group would necessarily (except when they by chance ComDose a familiar hone o r z i code ~ number). Indeed, iinck there are an &finite number numbers, introduce changes in grouping pattern (e.g., six-item lists divide into two groups of three. but a person cannot possibly have a stored representation of each of them, five- and seven-item lists do not). We used the same list lengths for all except the nursery-school children; the consequent ceiling effects for the older subjects must be taken Whether a series of n digits is treated as n separate items, o r as one i n t o in evaluating the results. multidigit item with n places, that Series i n v ~ l v e the s Same information in subjects were randomly assigned to the different so~nd-patternconditions. presentation essentially the same form; namely, n ordered digits, each of which can was blocked for lists o f a particular type; for example, all five lists of length six grouped were presented together. Within each condition, subjects were assigned to one of four diflerent assume 10 different values. It has also been proposed that subjects chunk digits when numeric presentation orders. Before each block, subjects were told the length of the list and whether it patterns (e.g., 1 4 2 5 3 6) are detected in a list, formulating a rule on the would be ungrouped o r grouped. This was done to eliminate the possibility that familiarity with particular melodies o r prosodic patterns might lead subjects to anticipate. after the first basis of this pattern and using it to regenerate the sequence (Restle, 1970). few items, either list length o r grouping pattern, something that would be possible with However, there is reason to questidn whether such strategies are used in patterned sound but not with monotone. span tasks involving rapid auditory presentation. Obvious regularities are Materials clnd appnrclttrs. Since grouping was varied for all sound pattern conditions, we avoided by experimenters in constructing sequences. If patterns do needed to find melodic and prosodic patterns both with and without natural temporal breaks. remain, it seems doubtful that the subject would have time to detect them For the prosody condition, ungrouped lists involved a pattern common in declarative with fast presentation. Furthermore, if the subject sometimes perceived sentences; grouped lists used a pattern common in a question-answer sequence. i.e.. rising intonation in the first group and falling in the second. The prosodic patterns were natural rclther patterns, one would expect wide fluctuations in the number of elements the than exaggerated. For the melody condition. ungrouped lists involved nursery tunes with a subject could recall depending on whether a pattern was perceived. But relatively constant beat. where the first phrase was the same length as the list ( w hcn the heat span tasks have been used in I Q tests precisely because the number of was not completely constant we altered it slightly to make it so). G~.uupeJlists involve runes with pauses corresponding to the temporal grouping pattern. items recalled by a particular individual is stable. - -

--

.

ofiultidigit

8

HUTTENLOCHER AND BURKE Grouped Length 4 5 6 7 8

Melody "Frere Jacques" "Rain, Rain, G o Away" "Brahms Lullaby" "Hickory. Dickory Dock" "The Bear Came over the Mountain"

Ungrouped Length 4 5 6 7

8

9

D E V E L O P M E N T O F M E M O R Y SPAN

--

Melody "Ba. Ba, Black Sheep" "Row. Row. Row Your Boat" "On Top of Old Smokey" "Alphabet Song" "Lavender Blue"

Lists of digits were recorded on a Sony TC-252 tape recorder. The lists consisted of the digits zero to nine, drawn from tables of random numbers with the following restrictions: Run length could not exceed two and no digit was repeated within a list. For each list length, total presentation time was the same for grouped and ungrouped conditions. Presentation rate for grouped lists was always one digit per 0.5 sec with a I-sec interval between groups. Thus, presentation rates for ungrouped sequences of lengths four, five, six, seven, and eight were one digit per 0.75, 0.70, 0.67, 0.64, and 0.63 sec, respectively. A recorded signal, "ready," preceded each sequence by 1.5 sec. Subjects. The subjects were 270 children enrolled in middle-class suburban nursery schools o r elementary schools. There were 90 nursery school children (mean CA = 4.6) and 60 children at each of three grade levels, first grade (mean CA = 7.0), third grade (mean CA = 9.21, and fifth grade (mean CA = 11.0). Procedure. Subjects were tested individually. All subjects were given the following instructions: "We are going to play a game to see how good your memory is. You will heara list of numbers. Listen very carefully and a s soon a s the list ends, say the numbers back to me in the same order you heard them in. Say them back o r sing them back o r any way you like. Be sure you give back all the numbers in the same order. I will tell you how many numbers will be in the list before you hear it. Also, some of the lists of numbers will be grouped, that is. there will be a little pause in the middle of the numbers. Before each list of numbers you will hear a voice say 'Ready' and then you will hear the numbers. As soon as they are finished. say them back." Subjects received two practice lists, one grouped and one ungrouped, of a length one digit less than the shortest experimental list, and then 40 experimental lists (30 for nursery school subjects). A break of 3 min was taken after half the lists had been presented, during which the subject removed the earphones and chatted with the experimenter. The procedure was modified slightly for the nursery school subjects. The instructions were simplified and encouragement was given more frequently. T o explain the task more thoroughly, the experimenter said a practice list in the following way before starting the tape recorded practice sequence. "Now if you hear 'Ready . . . three, five,' what would you say?" If necessary the task was re-explained and another practice list was given. Scoring. Let us consider certain measurement problems in assessing ordered recall when subjects respond aloud. In the usual scoring procedure. an item is scored as correct when it is the correct item in the correct ordinal position. Ifthere is an omission o r an intrusion, not only that item but all later items are scored a s incorrect, even if they are the correct items given in the correct order. For example, if the list were 3 1 4 2 6 5, and the response was 3 4 2 6 5, only the 3 would be scored as correct. Such a scoring procedure may not provide a good estimate of what the subject knows about alist of items. Indeed, the procedure seems clearly unmotivated when one considers the alternative of starting the scoring at the end of the list and working backwards. In this case, 4 2 6 5 would be scored as correct and 3 would be treated a s an error. Thus the usual scoring procedure penalizes the final positions of the list when there are omissions o r intrusions. thus underestimating recency. This issue is important here because our concern is with the shape of the serial position curve across age. Some investigators have avoided this problem by using a free recall measure for ordered recall. While such a scoring

nlclhod is acceptable for words, it seems inappropriate for digits. Since there are only 10 ,liFir. subjects could get most items right i n a list ofeight items by simply counting from one to cipht. Wc developed an adjusted scoring procedure to help overcome these problems by allowing slrdit when a number appeared out of its original position but in a correctly ordered sequence. ;\ number in its correct serial position was always scored as correct, and an omission, illtnlsion, or repetition always resulted in loss of one total point. For or~iissior~s. no credit was rccordcd in the position of the omitted item and the rest of the list was scored a s correct. For i,ltrrr.tions, half credit was assigned to the serial positions of the two items surrounding the intruding item; e.g., if 2 4 3 5 8 1 9 were the response to 2 4 3 8 1 9, it would be scored a s I I !4 % I I. Forintrulist intrusiot~s,% credit was assigned to the serial positions of items surrounding [he intruding item, as well a s to the original position of the intrusion; e.g.. if 2 4 8 1 3 9 were the response, it would be scored a s 1 1 55 1 %%. If two correct items exchanged positions, each u.;ls scored 95, e.g., if 4 2 3 8 1 9 were the response, it would be scored as !4 M I I I 1.

RESULTS Table 1 shows the mean number of correct digits for grouped and ungrouped lists for each of the three sound conditions for the nursery school, first, third, and fifth grade subjects based on unadjusted scores. We TABLE l MEANNUMBEROF DIGITSRECALLEDI N CORRECTSERIALPOSITIONPER LIST" List length 4

Sound pattern

G

5 U

G

6 U

G

7

U

G

Across lengths

8 1'

G

U

G

U

3.15 3.02 3.13

2.30 2.14 2.32

Nursery school Mono. Pros. Mel.

3.69 3.38 3.48

3.33 2.91 3.23

3.07 2.79 3.32

2.31 2.29 2.49

2.71 2.90 2.60

1.27 1.23 1.25

First grade Mono. Pros. Met.

4.58 4.82 4.53

3.35 4.30 3.83

4.25 5.30 4.69

2.45 3.52 2.89

3.38 4.86 4.35

2.22 3.42 3.23

2.93 4.66 3.59

1.81 2.41 2.44

3.79 4.91 4.29

2.46 3.41 3.10

8 5.97 6.19

5.00 5.01

5 5.65 4

4.29 4.80 4.81

Third grade Mono. Pros. Mel. fifth grade

L\, Mono. Pros. Mel.

4.91 4.92 4.94

4.77 4.72

0

5.58 5.86 5.55

4.71

% 4.31

5.90 5.86 6.26

" G = Grouped presentation, U = Ungrouped presentation.

, 1967, 74, Hagen. J. W.. Meacham, J. A., & Mesibov, G. Verbal labeling. rehearsal, and short-term 1-15. memory. Cognitive Psychology, 1970, 1, 47-58. Burke, D. Developtnenral changes in speech perception: Accuracy and respot~setime llarcum, E. R. Parallel functions of serial learning and tachistoscopic perception. for identfiing words in noise. Unpublished doctoral dissertation. Columbia Psychological Review. 1967, 74, 5 1-62. University, 1975. Harris, G. J., & Burke, D. M. The effects ofgrouping on short-term serial recall of digits by Bush, E. S., & Cohen, L. B. The effects of relevant and irrelevant labels on short-term children; developmental trends. Child Developmet~r.'972. 43, 710-716. memory in nursery school children. Psycironomic Science, 1970, 18, 228-229. Ham's, G. J . , & Fleer. R. Memory scanning in mental retardates: Evidence for a central Calfee, R. C. Short-term retention in normal and retarded children as a function of memory processing deficit. Journal of Experimental Child Psychology. 1974, 17, ,452-459. load and list structure. Research trnd Development Center Technical Report No. 75, Hintzman, D. L., Block, R. A., & Summers, J. J. Contextual associations and memory for University of Wisconsin, Madison, 1969. serial position. Jorrrnol o j E.rperimentrr1 Psycl~ology,1973, 97, 220-229. Cavanagh, 3. P. Relation between the immediate memory span and the memory search rate. Hoving, K., Morin, R., & Konick. D. Recognition reaction time and size ofthe memory set: A Psychologiccrl Review, 1972, 79, 525-530. developmental study. Psyclrotronric Science. 1970. 21, 247-248. Cole, M., Frankel, F., & Sharpe, D. Development of free recall learning in children. Huttenlocher, J. The origins of language comprehension. In R. Solso (Ed.). Theories in Developmenral Psychology, 197 1, 4, 109- 123. Conrad, R. Acoustic confusions and memory span for words. Nature [London), 1963, 197, cognitive psychology. Potomac. MD.: Lawrence Erlbaum. Assoc.. 1974. 1029- 1030. Jacobs, J. Experiments in "prehension." Mind, 1887, 12, 75-79. Conrad, R. Acoustic confusions in immediate memory. British Jolrrncrl of Psychology, 1964, Jahnke, J. C. Presentation rate and the serial-position effect of immediate serial recall. 55, 75-84. Jo~rrrralof Verbnl Lenrt~itrpand Verbal Beho~.ior.1968. 7, 605-612. Conrad, R. Order error in immediate recall of sequences. Journcrl of Verbal Lennrit~g~ t r d Jahnke, J . C. Probed recall of strings that contain repeated elements. Jorrrtrcrl of. Vcrhol Verbal Behni~ior,1965, 4, 161- 169. Lerrrrring crnd Verbal Be/rni.ior. 1970. 9 , 450-455. Conrad. R. The chronology of the development of covert speech in children. ~ e ~ ~ e l o ~ n ~ e Johnson, ntal N. The role of chunking and organization in the process of recall. In G. Bower. Psycl~ology,1971, 5, 398-405. (Ed.), The psyi,lrology of Ii~crrnitrga t ~ dn r o t i ~ ~ n t i Nrw ~ ~ n .York: Academic Press. 1970. Conrad. R., & Hull, A. J. Information, acoustic confusion and memory span. British Jorrrtral Vol. 4. of Psychology. 1964, 55,429-437. Kaplan, E. L., & Kaplan. G. A. The prelinguistic child. IF!. Eliot (Ed.).H~rrnrrrr