- Email: [email protected]
Learning is organized by chunking
JOURNAL
OF VERBAL
LEARNING
AND
VERBAL
Learning
BEHAVIOR
15,
(1976)
313-324
is Organized
by Chunking
HERMAN BUSCHKE Albert
Einstein
College
of Medicine
Chunking of items, with further organization of the chunks, has long been supposed to play a significant role in verbal learning. Spontaneous chunking in natural free recall learning is demonstrated directly by identifying clusters of items that recur together in different retrieval attempts, demarcated by different items or clusters. Trial-by-trial delineation of actual chunks and their organization in typical individual learning protocols demonstrates that items are spontaneously clustered into many small recurrent chunks, which remain intact when they are juxtaposed in higher-order organization of the basic chunks. Identification of the actual chunks in each retrieval permits trial-by-trial analysis of organization during verbal learning in terms of both basic clustering and higher-order organization of recurrent, well-defined clusters. Identification of chunking also allows analysis of the increasing rate of retrieval during learning in terms of individual items, items within chunks, and chunks.
Chunking and organization in memory have been investigated vigorously since Bousfield (1953) pointed out that items seem to be recalled in associated clusters, and Miller (1956) pointed out that limits in our capacity for processing information necessitate recoding by organizing items into “chunks” that can themselves be organized. Our understanding of such organization in memory and learning has been advanced greatly by the contributions of Tulving (1962; Tulving & Donaldson, 1972), Pollio (1964; Pollio et al., 1968; 1969), Mandler (1967; 1970; Mandler & Dean, 1969), Cofer (1967), Bower (1970), Kintsch (1970), Pellegrino and Battig (1974), and Martin and Noreen (1974), aswell asmany others. Most of the extensive research on organization in memory and learning has been concerned with demonstrating that retrieval in free recall learning is organized, with estimating the total amount of organization, and This work is supported by USPHS Grants MH17733 to H. B. from NIMH, NS-03356 from NINDS, and HD-01799 from NICHD. I thank Christine Sinclair-Prince for experimental and editorial assistance. Requests for reprints should be sent to Herman Buschke, M.D., Department of Neurology, Albert Einstein College of Medicine, Bronx, New York 10461. Copyright IQ 1976 by Academic Press, Inc. Ail rights ofreproduction in any form reserved. Printed in Great Britain
313
with showing that various kinds of grouping or categorizing by either the subject or the investigator will increaserecall, and that interference with subjective organization will hinder recall. We have not had a method for analyzing the actual organization on each trial of learning in terms of the actual chunks that are supposed to be organized in learning. Measurement of subjective organization has been restricted to consideration of how many n-tuples on Trial YE recur on Trial n + 1, without considering the (size of) actual clusters or the difference between clusters that only appear on Trials n and n + 1 and more robust clustersthat recur on all trials. Analyses of hierarchical clustering, which have been concerned with the actual organization, seemto assumesomeunderlying organization that is reflected by and can be inferred from recall over several or many trials; this is not very helpful if we need to see the organization on each trial to seethe changes in organization that are supposedto occur in learning. To show spontaneouschunking and organization of chunks in learning and to see the growth of organization in learning, we need to identify the actual chunks on each trial of learning. Martin and Noreen (1974) have
314
HERMANBUSCHKE
shown chunking in serial learning by identifying serially ordered subjective sequences in individual learning protocols. They present an insightful analysis of organization and learning, and make it clear that we need to identify subjective sequences or chunks and analyze their organization in order to understand what happens during learning. The purpose of this note is to show (a) that what happens in natural free recall learning of randomly ordered, unrelated items is that items are spontaneously clustered into many small recurrent chunks that remain intact when the basic chunks are grouped in higher-order organization, and (b) to show how well-defined recurrent chunks can be identified on each trial, so that the growth of organization in learning can be analyzed. This is shown by direct demonstration of the actual clusters on each trial in individual learning protocols. It is necessary to show individual protocols so the reader can see the clustering, because I do not know how to summarize these findings across subjects. These clusters are identified by observing that the items in each cluster appear together in different retrieval attempts, and are demarcated by different items or clusters on different retrieval attempts. The identification of such chunks simply requires comparison of all possible chunks in each retrievalwith all possible chunks in all other retrievals. I analyzed these protocols by eye, but we expect to have a computer program for this rather tedious but straightforward analysis (Zangen, Ziegelbaum, & Buschke, 1976) ; if the reader discovers some small chunks that escaped me, it will just help to show that recurrent chunks can be identified in spontaneous retrieval of unrelated items. MATERIALS
AND METHODS
These protocols were obtained by asking subjects for repeated spontaneous retrieval without any further presentation after a list of 40 “unrelated” items was presented just once. The subjects were allowed to recall the items
in any order, and were given as much time and encouragement as necessary to obtain maximum retrieval on each recall attempt. Their verbal responses were tape-recorded so that the temporal course of retrieval could be documented by simple timing with a stopwatch. A week later the subjects were unexpectedly asked to attempt one more spontaneous retrieval of this list, to evaluate the stability of their organization. After the final delayed retrieval, forced-choice recognition was tested using distracters that were conceptually similar to the list items. The subjects were tested individually, and were paid for their participation. Each subject received only a single presentation of the list, at his or her own rate. A different kind of presentation was used for each subject. A conventional written presentation of the items was used for the first subject, who read the items aloud from 3 x 5 cards, at her own rate. The second subject received an unconventional presentation that requires phonetic processing (Cermak, Schorr, & Buschke, 1970) reading aloud the items which were typed backwards on cards. For example, she had to decode “hsif” into “fish.” The third subject received a “cognitive presentation” of each item, a description or a definition from which he had to infer what the item was. For example, after reading a card that said “Use this item twice a day to keep your teeth clean,” he responded “toothbrush.” The definitions used for the cognitive presentations and the 40-word list come from a different study by Erdelyi, Buschke, and Finkelstein (in preparation). The use of such cognitive presentations (Buschke, in press) tells us that the subject attended to each item, thought about each item, that each item was already in his permanent lexicon, and that each item was retrievable. In addition, the use of presentations which require the subject to name the item for himself right from the beginning starts off the learning process with a spontaneous retrieval from long-term storage. This seems like a good way to start, because the
a-20-75
iron dice comb bell feather bicycle bottle umbrella W” chair table
ma5 tree toaster fish heart chain hook flas can;l1e arrow glasses boat funnel football hat ladder television broom snail toothbrush hourglass scissors pineapple bat telephone book ;;E;rS
SINGLE 'RESENTATION
C.H.
20 21 22 23 24 25 26 27 28 29 30
13 14 15 16 17 18
2 3 4 5
1
funnel telephone television umbrella ladder hook bell iron book watch toothbrush comb pineapple feather hourglass glasses flaq
snake key table chair fish
FIG.
table bell
O:ll 0:15
B
4:Ol
0:54 0:58 1:05 1:09 1:14 1:lB 1:*2
I =I4:56
_
comb lwatch
boat bat football funnel umbrella OCtoDUS snaii fish telephone television chair table snake ladder bell feather pineapple
“““L
“..,” 3
0:~ O:*l
I 2:23 . 0
F 1;46 A .
SPONTANEOUS RETRIEVAL 2
*:39
:j:;
1,50 1:s
1:30 37 ii,,
I---bell fish snail
4
I
4 1:lO 1:14 1:19 1:*4 1:*9 1:34 1: 1:45 1:52 1:s *:07
ol;;
5
1, Spontaneous retrieval after a single written presentation of each item,
football snail octopus fish feather umbrella book television telephone flxl
noun tnnthhrllch comb bat
xmas tree toaster wm:;
o:oo u:o3 ",i;;
. . A
7
0
0:*3
WEEK LATER
316
HERMANBUSCHKE
greatest difficulty in selective retrieval from long-term storage during verbal learning (Buschke, in press) seems to be the initial spontaneousretrieval, after which subjectsare usually able to maintain retrieval quite well (Buschke, 1974, 1975). Presentations which require the subject to produce each item initially seem appropriate whenever there is any question about what the subject is doing with each item and whether the item is retrievable. RESULTS
Retrieval after Conventional Presentation Figure 1 shows the learning protocol of a young woman who repeated spontaneous retrieval after a single presentation of the 40 item list shown on the left. Each of the 40 items was typed on a 3 x 5 card, which she read aloud at her own rate, in the order shown. Each retrieval is shown in the order in which she retrieved the items. The temporal course of retrieval is shown by the time elapsedfrom the onset of retrieval, in minutes and seconds.The chunks are labeled by letters. Items that were retrieved individually, not as part of a cluster, are marked by black dots. The basicchunks denoted by the letters were identified by observing that those items appeared together in more than one retrieval attempt, and that such chunks were demarcated by different items or clusters on different retrieval attempts. For example, the items in cluster F (telephone and television) recur together on all retrievals, including delayed retrieval 1 week later. On Trial 1 F was demarcated by E and “umbrella,” on Trial 2 F was demarcated by “book” and “flag,” on Trial 3 by B and A, on Trial 4 by “pineapple” and “flag,” on Trial 5 by El and the end of retrieval, and on the delayed retrieval F was demarcated by K and E,. Therefore it seems reasonableto identify F asa basic well-defined chunk. While F seemsto represent a cognitive clustering of two semantically related items
that were separatedin the initial presentation, other chunks, such as E (football and funnel) appear to reflect chunking basedon proximity in the original sequential presentation. The chunks are relatively small. Some chunks increaseslightly asadditional items are added. For example, C (“Xmas tree” and “toaster”), which appears on Trials 1 and 2, isincreasedby the addition of “iron” on Trial 3 to form the larger cluster CZ, which also includes the new small cluster C, (“toaster” and “iron”) that recurs in the delayed retrieval a week later. Some new clusters arise on successive retrievals; these are marked by circled letters. For example, “bell” and “ladder” which were retrieved as individual items on Trial 1, appear together on Trial 2 as cluster I, which recurs on all subsequent retrievals. The number of individually recalled items, marked by black dots, decreasesover repeated retrievals. Somewhat fewer items were retrieved spontaneously 1 week later, but most of the items in delayed retrieval were still retrieved in the same clusters as before. Although items usually are part of just one chunk, at least in organization by adults, an item can be included in more than one chunk, and can alsobe retrieved alone despiteprevious chunking. Although clusters were sometimes demarcated by long pauses,such asthe pausesbefore and after cluster H (“hourglass” and “glasses”) on Trial 1, many clusters are not bounded by obvious pauses in retrieval. In general, it appears that more accurate identification of chunks in retrieval can be achieved by using the criteria describedthan by relying on pauses in retrieval, partly becausethe pausesbetween chunks become shorter as the chunks are organized. However, when longer retrieval pauses do occur, they can confirm the clustering shown by retrieval of items together on different retrieval attempts. It appears that spontaneous clustering of items into small, well-defined chunks, which also are organized, is a basic process in natural free recall learning. Thesebasic chunks
IDENTIFICATION
are stable and recurrent, and remain intact when they are associatedwith other chunks as higher-order organization develops; items in different juxtaposed chunks are not reorganized into new chunks. The higher-order organization of the chunks themselvesis demonst,ratedin Figure 2, which C.H.
FIG. 2. Organization of chunks in repeated retrieval after a single written presentation of each item.
shows the relative ordering of chunks in each retrieval, after removal of individually retrieved items (marked by black dots in Figure 1). Although Figure 2 shows that there was increasing organization of chunks over repeated retrieval attempts, the organization of chunks doesnot seemasextensive as the basic organization of individual items into recurrent clusters. Figure 2 also shows that most of the items retrieved in the delayed retrieval a week later were retrieved aspart of the samechunks asbefore, but the organization of chunks in the delayed retrieval was lessthan on Trials 4 and 5 a week before. Retrieval after Phonetic Processimg Figure 3 shows the repeated spontaneous retrieval of another young woman after a single presentation of the 40 item list shown on the left. Each item wastyped backwards on
a 3 x 5 card, so that shehad to sound out each word; for example, she had to decode “hsif” into “fish.” This unconventional kind of presentation (Cermak, Schnorr, & Buschke, 1970)presumably requires somephonetic pro-
OF CHUNKING
317
cessingand may interfere with rehearsal and cognitive processing. After she had sounded out each of the words at her own rate, she retrieved the items verbally in standard English. Her protocol also shows increasing organization by the formation of small recurrent clusters, with increasing organization of those clusters in later retrievals, and persistence of that organization in the final delayed retrieval a week later. Some of her chunks, such as B (“fish, ” “heart,” “chain,” “hook,” “flag”) are larger and reflect the serial ordering of those items in the initial presentation. Most of her chunks show a considerable amount of internal. organization, with preservation of the same sequential order of the items in a chunk. Some chunks, such as B on Trial 1 are demarcated by long pausesbefore and after. On Trial 2 the pausebetween chunks B and A is no longer extensive, although the pause between chunks B and C is still substantial. This subject showed the increasing rate of retrieval (Figure 7) which, along with increasing accuracy of retrieval, is one of the two major characteristics of verbal learning. It appearsthat someof the increasein her rate of recall may be accounted for by increasingly rapid retrieval of the items within a chunk and some may be accounted for by increasingly rapid transition from one chunk to another as higher-order organization of the chunks themselvesdevelops during learning. This protocol is compatible with the reasonable hypothesis that increasing rate of retrieval in verbal learning may be at least partly due to increasing chunking and organization of chunks in retrieval. Figure 4 shows her higher-order organization by ordering the clusters in retrieval, after deletion of individually retrieved items. As learning progressed, she was able to retrieve more chunks without interposition of individually retrieved items, and developed an extensive and persistent higher-order organization of the basic chunks formed during learning.
funnel football hat ladder television broom snail toothbrush hourglass scissors pineapple bat telephone book octopus watch iron dice comb bell feather bicycle bottle umbrella W" chair table key snake
boat
xmds tree toaster fish heart chain hook flag candle arrow glasses
SINGLE PRESENTATION
11 12 13 14 15 1C li I 1CI l! 3 2c ) 2: 1 2: I 2: 3 2. I 215 215 2' 1 218 2' 3 31D 31 32 33 34 35 36 37 38 39 40
ia
2 3 4 5 6 7 8 9
1
0:5R I:07 1:09 1:26 1:35 1:42
1:5! 3:oc 3:O' 3:12 3:lf 4:4; 5:3t 5:5; 8:2C 8:46 R:5f
1:s~
Spontaneous
. . . . . .
FIG.
I
H
G
F ;;:;
. .
*
",i",;
. r t
0%
ii:",
0:21 0:24 0:33
0:18
D
c
B
candle umbrella _ feather bell 1 adder bat key
3.
jJ 0:oo
H 0:03 0:13 0:lG
arrow 9 glfisses
-%?brush watch snail octopus pineapple snake bicycle table _ chair telephone book
Xmas tree toaster fish heart chain hook flag boat funnel football hat
1 l-
2:06 2:os
2:13 4:20
I .
o:57 1:ol
0:38 0~43 0~46 0~52
0~34
0~12 0:15
O:OB o:io
0~02 0~05
0~00
4
* ,, " . r c
B
A
key feather bell watch
boat funnel football 1 hat 1 ladder 1 broom 1 toothbrush
xmas tree toaster I fish hook chain heart flag
SPONTANEOUS
3
. 4:2E ,@ 5:04
L :i:':
1:3t
"
l
0:59
,,
l
",i;;
0:43
0:33
0:13 0:1-l 0:25 0!20
0:09 o:ll
0:02 0:07
P
book broom
L
F\
4
G
C
B
J,
I,
A
1:07
0~51
gun table
bell
1:51l
1:33
1:l I:22
I pin fea
L-iii
5
,- \
Xmas tree toaster
1 candle 0:07 glasses o:oe arrow 0~11 fish 0~13 heart 0~15 l-----d chain 0:lG flag O:IB hook 0~21s boat o:2e funnel 0~30 football 0:32 hat
o:os
0~00 0~02
pi”eap “J” feather key bat
chair tab!e
telephone-
7
umbkella gun
candle glasses arrow fish chain heart hook flag boat funnel football hat
Xmas tree toaster
1
0:oo
O:50 0:52 0:56
c
1
B
A
RETRIEVAL
I,
C
26 2;
14
1:15 1:2G
13
0:31
WEEK xmas tree toaster glasses candle arrow fish heart chain flag hook
0:09 0:12 0:lB
0:03 0:06
0:oo
N
z:;:,
snail octopus
J,
E
D
;I;:
ii:;
;f;;
0:59
0:52 0:55
;;y;;;;;'
0:51
m 1:03 I:07
C
0:23 B 0:25 0:26 0:31 0:3R 0:46
11
A
LATER
football hat toothbrush broom ladder watch
3 4 5 6 1 B 9 10 11 boat 12 funnel
:
0:29
Oil4 0:16 B 0:17 0:19 0:20 0:2G 0:27
;:;;
0:07
A 0:oo 0:03
retrieval after decoding a single presentation of each item written backwards.
watch glasses candle snake
Xmas tree toaster fish hook heart chain flag boat funnel football hat bell broom toothbrush ladder snail octopus
2
IDENTIFICATION
5
A '1 9 B C1 0 D M IO E3
6
319
OF CHUNKING
delayed retrieval a week later, he retrieved somewhat fewer items, more slowly. While this younger subject did show considerable clustering of individual elements which was still apparent in delayed retrieval a week later, Figure 6 shows very little higherorder organization of the clusters themselves.
J, F 4 p L 4 G
DISCUSSION
These individual protocols demonstrate directly that retrieval in natural free recall FIG. 4. Organization of chunks in repeated retrieval learning is organized by spontaneous clusterafter decoding a single presentation of each item written backwards. ing of items into small recurrent chunks that remain intact when the basic chunks are Retrieval after Cognitive Processing organized as learning proceeds. These protoFigure 5 shows repeated spontaneous re- cols provide typical illustrations of such trieval of this 40 item list by a 12-year-old boy, organizing by chunking, so the reader can after a single “cognitive presentation” by confirm that recurrent chunks can be identified means of descriptions or definitions from by finding clusters of items that appear which he inferred the items to be retrieved. For together in different retrievals and are demarexample, after he read the description “use cated by different items and chunks on different this item twice a day to keep your teeth clean,” retrievals. It appears that what happens in free recall he said “toothbrush.” This kind of cognitive presentation tells us that he attended to each learning is that the items are organized into item, thought about each item, that each item small stable chunks which also are organized. was in his permanent memory, and that he Because the basic chunks are directly apparent could retrieve each item. The use of such in retrieval, the actual organization of items cognitive presentations seems appropriate be- and chunks on each trial can be described and cause it provides these necessary assurances, the changes in organization during learning and seems interesting because cognitive pre- can be analyzed. This is shown clearly by sentations allow the experimenter to vary the spontaneous retrieval after a single presenkind of cognitive processing used at the time of tation, which is a special case of selective reminding and restricted reminding (Buschke, encoding (Buschke, in press). This lZyear-old boy retrieved nearly as 1973). The advantage of these paradigms is many items as the adults. In the forced-choice that they let subjects show what they have recognition test after the final delayed retrieval, learned by recall without presentation, which he recognized 39 of the 40 list items, like the shows true retrieval from long-term storage adult subjects who recognized 38 and 40 items. during learning, and permits organization of Figure 5 shows that he also organized the items retrieval without disruption by unnecessary into many recurrent chunks during learning. repeated presentation (Mandler & Dean, Some chunks, such as E (“funnel” and 1969). Free recall of unrelated items seems to “bottle”), appear to represent cognitive clus- be the appropriate way to determine whether tering on a semantic basis. Others, such as B items are normally cIustered into chunks that (“Xmas tree,” “chain,” “fish”), appear to be also are grouped in order to process large based more on proximity in sequential presen- amounts of information effectively. It seems tation than on conceptual relatedness. In appropriate to use some kind of selective
g-17-75 SPONiANEOUS
RETRIEVAL
FIG. 5. Spontaneous retrieval by a 12-year-old boy after inferring each item from its description
iron dice comb bell feather bicycle bottle umbrella gun chair telephone key snake
snail toothbrush hourglass scissors pineapple bat table book KtOl)"S
xms tree toaster fish heart chain hook flag candle arrow glasses boat funnel football hat ladder television
SINGLE IESENTATION
t&S. LATER
3
. . .
E
C
b
7:07 7:18 *:50 11:03 11:11
0:21 0:x 0:s 0:31 2:*9 3:43 x:50 4:19 4:22 495 5:oo 5:15
in a single cognitive presentation.
pineapple xmas tree chain snail television fish hook bat hat football watch hourglass bottle funnel candle key brorm
YEEK
IDENTIFICATION
FIG. 6. Organization of chunks in repeated retrieval by a lZyear-old boy after a single cognitive presentation.
reminding to minimize the disruptive effect of repeated presentation on the organization of retrieval; repeated retrieval after a single presentation is the kind of selective reminding that shows spontaneous organization of retrieval after the least possible presentation. The disadvantage of a singlesequentialpresentation is that organization may be limited becausesomeitems must be encoded before it is known what the rest of the items are, so that recoding may be necessary to group related items, and such grouping may be limited by the subject’s ability to remember related items that were presented earlier. In addition, the implicit constraint to avoid repetitions in order to recall as many different items as possiblein the necessarilysequential recall may prevent subjectsfrom showing that someitems may be part of several different chunks. Nonetheless, the individual protocols presentedhere clearly showthat retrieval in verbal learning is organized by clustering items into small recurrent chunks that remain intact when the chunks are grouped. These findings provide direct confirmation that retrieval is organized spontaneously by chunking even when subjects are not asked to order, group, or categorize the items in natural free recall. The analysis of organization shown here allows us to seethe actual chunks, and their organization, on each trial of learning. This lets us analyze organization in terms of the basic organization of items into chunks and the higher-order organization of the chunks. Since the actual composition of each chunk
OF CHUNKING
321
can be seen,the cognitive processinginvolved in the basic chunking and the grouping of chunks can be investigated. Analysis of chunking and grouping of chunks should help account for differences in rate of retrieval (Murdock & Okada, 1970) and for the increasing rate of retrieval during learning, as well as for the increasing number of items retrieved during learning. Figure 7 shows the increasing rate of retrieval of all items and of those items retrieved as part of a chunk on Trials 1, 2, 5 and 1 week later. Trials 3 and 4 were omitted for graphical clarity; Trial 2 is the first spontaneousretrieval without presentation. Initially there is a fast phase of recall, followed by a slow phaseas retrieval becomes more difficult. As learning proceeds,the rate of retrieval increases so that most of the items are retrieved in the fast phase. Although the rate of retrieval by the 12-year-old subject is slower than that of the adult subjects, it also increased over trials. A week later, the adults’ rate of retrieval was still nearly as high as on Trial 5, but the 12-year-old’s rate of retrieval was lower than it was on Trial 1. This may be related to organization by chunking and grouping of chunks during learning, since less of the 12-year-old’s total retrieval was due to chunked retrieval. The increasing rates and amounts of total and chunked retrieval in Figure 7 seemreasonably consistent with the chunking and higher-order organization of chunks shown in the preceding figures. The increase in rate of chunked retrieval, which may be due to increasing rate of retrieval of items in chunks as well as increasingly rapid retrieval of chunks, seemsto account for a substantial part of the increased rate of total retrieval. Identification of the actual chunks on each trial makes it possible to analyze rates of retrieval and changes in the rate of retrieval quite specifically in terms of the retrieval of individual items, the retrieval of items in chunks, and the retrieval of chunks, for example, in terms of time between individual items, time between items in chunks, and time
322
HERMAN
BUSCHKE
CH -ADULT
1.......1.‘...““‘,“,“,‘~‘.J I 3. 3’1567
1x3956789
,
I
3
4
5
6
7
P
9
lo
II
MJNUTES FIG. 7. Retrieval rate in repeated retrieval after a single presentation.
between chunks as learning proceeds. When extended recall is used, asit should in order to obtain the maximum retrieval necessary for accurate evaluation of learning (Buschke, 1973, 1974), it is necessary to analyze rate of retrieval, since, as Figure 7 illustrates, nearly the sametotal number of items may eventually be retrieved when enough time is provided for maximum retrieval at different rates. When extended recall is used, any correlation between organization and learning will be shown by correlation between organization and rate of retrieval, rather than number of items retrieved. Learning is generally shown by an increasing rate of retrieval, which presumably reflects ease of retrieval and eRecGvenessof encoding. Since it takes time to recall items sequentially, number of items recalled or probability of recall, which are customarily used to
measurelearning, really mean number of items recalled or probability of recall during some interval of time. Number of items recalled will depend on the amount of time allowed for recall; the number of items recalled in the standard brief recall period provides an estimate of the rate of retrieval during some fixed interval. Estimating the retrieval rate by the number of items recalled in a limited recall period may be useful when retrieval rate stays constant, but may be difficult when retrieval rate is not constant, since different estimates of learning could be obtained by using different recall periods. Since the constancy of recall rate and the appropriateness of any particular recall time can only be evaluated when retrieval rate over a longer period is analyzed first, and since extended recall should be used to obtain maximum retrieval on each trial, it seemsappropriate
IDENTIFICATION
to use extended recall and analyze retrieval rate more explicitly, including consideration of the effects of chunking and organization of chunks. Since it appears that natural free recall learning does involve spontaneous clustering of items into small recurrent chunks, such chunking should be taken into account when verbal learning is analyzed. Delineation of the basic chunks in learning, by identifying clusters of items that recur together in different retrievals and are demarcated by different items or chunks in different retrievals, should provide the information necessary for analyzing verbal learning in a way that takes the organization of retrieval into account. Analysis of verbal learning in terms of the basic chunking and the higher-order organization of chunks extends the analysis of “levels of processing” (Craik & Lockhart, 1972) to include levels of semantic processing, in retrieval and recoding as well as in initial encoding. Analysis of actual chunking should provide a more realistic basis for measurement of subjective organization during learning. The present findings indicate that it may not be appropriate to measure organization by counting the occurrence of n-tuples on Trials n and n + 1, since this ignores the fact that items are clustered in chunks of various sizes, some of which may persist throughout learning, while others may not. The simplest measure of organization is given by n - 1, where n is the number of items in a cluster. This measure provides the least possible discrimination between clusters of size n and n + 1, and between two clusters of n items and 1 cluster of 2n items. This measure can be interpreted as the minimum number of links needed to connect all of the items in a cluster. It is linearly related to the number of items in a cluster, and can include the higher-order grouping of basic chunks. The relative persistence of chunks can be taken into account by not counting the first occurrence of each chunk. It is conceivable that identification of re-
OF CHUNKING
323
current chunks might also be useful for analyzing some other kinds of organization. As the present findings suggest, it may not always be appropriate to assume, as some kinds of multidimensional scaling do (Fillenbaum & Rapoport, 1971; Shepard, Romney, & Nerlove, 1972; Romney, Shepard, & Nerlove, 1972), that every item in a set of items is necessarily related to every other item in that set, or that each item should be represented only once. For at least some sets of items, it seems more likely that some items may belong to more than one cluster but may not be related to all other items in the set (except trivially, because they are all members of the same general category). Also, in some cases items may be related only indirectly because the clusters to which they belong are related. In some experimental situations, all of the items may seem to be related even though every item may not actually be related to every other item. For example, the sequential retrieval of items in free recall has suggested that the organization of recall can be represented in terms of the proximity of each item to every other item. However, as the present findings suggest, it is possible that, while items are related to those other items that belong to the same chunks, items in different chunks may only appear to be related because the sequential nature of verbal recall results in an apparent ordering of items that may really be due to the necessarily sequential recall of different chunks. While it is certainly possible to represent the organization of a set of items as though every item were related to every other item in that set, even when they are not, it would seem more appropriate to determine experimentally whether every item is actually related to every other item or whether items are related only to some but not all of the other items in that set (and if so, what is related to what). When items are clustered in recurrent chunks, as in sorting experiments, for example, it would seem more appropriate to analyze their organization in terms of the
324
HERMAN
inclusion of items in specific chunks and organization of the chunks, than to ignore the experimentally obtained groupings in order to create a proximity matrix on the assumption that every item must be related to every other item. Analysis of chunking seems necessary to determine the actual organization and represent it most appropriately.
REFERENCES
BOUSFIELD,W. A. The occurrence of clusteringin the recall of randomly arranged associates. Journal of General
Psychology,
1953,49,229-240.
BOWER, G. H. Organizational
factors in memory. 1S-46. BUSCHKE, H. Selective reminding for analysis of memory and learning. Journal of Verbal Learning and Verbal Behavior, 1973,12,543-550. BUSCHKE, H. Spontaneous remembering after recall faihxe. Science, 1974,184,579-581. BUSCHKE, H. Retrieval of categorized items increases without guessing. Bulletin of the Psychonomic Society, 1975,5, 71-73. BUSCHKE,H. Retrieval in the development of learning. In N. J. Castellan, D. B. Pisoni, & G. R. Potts (Eds.), Cognitive Theory: Vol. ZZ. Hillsdale, New Jersey: Lawrence Erlbaum Associates, 1976. CERMAK, G., SCHNORR, J., & BUSCHKE, H. Word recognition as a function of speIIing direction during study and test. Psychonomic Science, 1970, 21, 127-128. COFER, C. N. Does conceptual organization influence the amount retained in immediate free recall? In Kleinmuntz, B. (Ed.), Concepts and the structure of memory. New York: John Wiley & Sons, 1967. CRAIK, F. I. M., & LOCKHART, R. S. Levels of processing : A framework for memory research. Cognitive
Journal
Psychology,
of Verbal
1970, 1,
Learning
and
Verbal
Behavior,
1972,11, 671-684. ERDELYI, M., BUSCHKE, H., & FINKELSTEIN, S. Spontaneous retrieval of words, pictures, and “Socratic presentations,” in preparation. FILLENBAUM, S., & RAPOPORT, A. Structures in the subjective lexicon. New York: Academic Press, 1971. JOHNSON,N. F. The role of chunking and organization in the process of recall. In G. H. Bower (Ed.), The psychology
of learning
and motivation.
York: Academic Press, 1970, Vol. 4.
New
BUSCHKE
KINTSCH, W., MILLER, R. F., & HOGAN, R. M. Semantic structure and clustering in free recall. Studies in mathematical learning theory and psycholinguistics, University of Colorado, 1970.
MANDLER, G. Words, lists, and categories. In J. L. Cohan (Ed.), Studies in thought and language. Tucson: University of Arizona Press, 1970. MANDLER, G. Organization and memory. In K. W. Spence & J. T. Spence (Eds.), The psychology of learning and motivation. New York: Academic Press, 1967, Vol. 1. MANDLER, G., & DEAN, P. J. Seriation: Development of serial order in free recall. Journal of Experimental Psychology, 1969,81,207-215. MARTIN, E., & NOREEN, D. L. Serial learning: Identification of subjective sequences. Cognitive Psychology, 1974,6,421-435. MILLER, G. A. The magical number seven, plus or minus two: Some limits in our capacity for processing information. Psychological Review, 1956, 63,81-97.
MURDOCK, B. B., JR., & OKADA, R. Interresponse times in single-trial free recall. Journal of Experimental Psychology, 1970,86,263-267. PELLEGRINO, J., & BATTIG, W. F. Relationships
higher order organizational recall. Journal of Experimental
among measures and free Psychology,
1974,
102,463-472.
POLLIO, H. R., KASSCHAU, R. A., & DENISE, H. E. Associative structure and the temporal characteristics of free recall. Journal of Experimental Psychology, 1968,76,190-197. POLLIO, H. R., RICHARDS, S., & LUCAS, R. Temporal properties of category recall. Journal of Verbal Learning and Verbal Behavior, 1969,8, 529-536. POLLIO, H. R. Composition of associative clusters. Journal of Experimental Psychology, 1964, 67, 199-208. ROMNEY, A. K., SHEPARD, R. N., & NERLOVE, S. B. (Eds.), Multidimensional scaling, Vol. ZZ: Applications. New York: Seminar Press, 1972. SHEPARD, R. N., ROMNEY, A. K., & NERLOVE, S. B. (Eds.), Multidimensional scaling, Vol. I: Theory. New York: Seminar Press, 1972. TULVING, E. Subjective organization in free recall of “unrelated” words. Psychological Review, 1962, 69,344-354.
TULVING, E., & DONALDSON, W. (Eds.), Organization of memory. New York: Academic Press, 1972. ZANGEN, M., ZIEGELBAUM, P., & BUSCHKE, H. Cluster: A program for identifying recurrent clusters. Behavior Research Methods for Znstrumentation, in press. (Received October 6, 1975)
OF VERBAL
LEARNING
AND
VERBAL
Learning
BEHAVIOR
15,
(1976)
313-324
is Organized
by Chunking
HERMAN BUSCHKE Albert
Einstein
College
of Medicine
Chunking of items, with further organization of the chunks, has long been supposed to play a significant role in verbal learning. Spontaneous chunking in natural free recall learning is demonstrated directly by identifying clusters of items that recur together in different retrieval attempts, demarcated by different items or clusters. Trial-by-trial delineation of actual chunks and their organization in typical individual learning protocols demonstrates that items are spontaneously clustered into many small recurrent chunks, which remain intact when they are juxtaposed in higher-order organization of the basic chunks. Identification of the actual chunks in each retrieval permits trial-by-trial analysis of organization during verbal learning in terms of both basic clustering and higher-order organization of recurrent, well-defined clusters. Identification of chunking also allows analysis of the increasing rate of retrieval during learning in terms of individual items, items within chunks, and chunks.
Chunking and organization in memory have been investigated vigorously since Bousfield (1953) pointed out that items seem to be recalled in associated clusters, and Miller (1956) pointed out that limits in our capacity for processing information necessitate recoding by organizing items into “chunks” that can themselves be organized. Our understanding of such organization in memory and learning has been advanced greatly by the contributions of Tulving (1962; Tulving & Donaldson, 1972), Pollio (1964; Pollio et al., 1968; 1969), Mandler (1967; 1970; Mandler & Dean, 1969), Cofer (1967), Bower (1970), Kintsch (1970), Pellegrino and Battig (1974), and Martin and Noreen (1974), aswell asmany others. Most of the extensive research on organization in memory and learning has been concerned with demonstrating that retrieval in free recall learning is organized, with estimating the total amount of organization, and This work is supported by USPHS Grants MH17733 to H. B. from NIMH, NS-03356 from NINDS, and HD-01799 from NICHD. I thank Christine Sinclair-Prince for experimental and editorial assistance. Requests for reprints should be sent to Herman Buschke, M.D., Department of Neurology, Albert Einstein College of Medicine, Bronx, New York 10461. Copyright IQ 1976 by Academic Press, Inc. Ail rights ofreproduction in any form reserved. Printed in Great Britain
313
with showing that various kinds of grouping or categorizing by either the subject or the investigator will increaserecall, and that interference with subjective organization will hinder recall. We have not had a method for analyzing the actual organization on each trial of learning in terms of the actual chunks that are supposed to be organized in learning. Measurement of subjective organization has been restricted to consideration of how many n-tuples on Trial YE recur on Trial n + 1, without considering the (size of) actual clusters or the difference between clusters that only appear on Trials n and n + 1 and more robust clustersthat recur on all trials. Analyses of hierarchical clustering, which have been concerned with the actual organization, seemto assumesomeunderlying organization that is reflected by and can be inferred from recall over several or many trials; this is not very helpful if we need to see the organization on each trial to seethe changes in organization that are supposedto occur in learning. To show spontaneouschunking and organization of chunks in learning and to see the growth of organization in learning, we need to identify the actual chunks on each trial of learning. Martin and Noreen (1974) have
314
HERMANBUSCHKE
shown chunking in serial learning by identifying serially ordered subjective sequences in individual learning protocols. They present an insightful analysis of organization and learning, and make it clear that we need to identify subjective sequences or chunks and analyze their organization in order to understand what happens during learning. The purpose of this note is to show (a) that what happens in natural free recall learning of randomly ordered, unrelated items is that items are spontaneously clustered into many small recurrent chunks that remain intact when the basic chunks are grouped in higher-order organization, and (b) to show how well-defined recurrent chunks can be identified on each trial, so that the growth of organization in learning can be analyzed. This is shown by direct demonstration of the actual clusters on each trial in individual learning protocols. It is necessary to show individual protocols so the reader can see the clustering, because I do not know how to summarize these findings across subjects. These clusters are identified by observing that the items in each cluster appear together in different retrieval attempts, and are demarcated by different items or clusters on different retrieval attempts. The identification of such chunks simply requires comparison of all possible chunks in each retrievalwith all possible chunks in all other retrievals. I analyzed these protocols by eye, but we expect to have a computer program for this rather tedious but straightforward analysis (Zangen, Ziegelbaum, & Buschke, 1976) ; if the reader discovers some small chunks that escaped me, it will just help to show that recurrent chunks can be identified in spontaneous retrieval of unrelated items. MATERIALS
AND METHODS
These protocols were obtained by asking subjects for repeated spontaneous retrieval without any further presentation after a list of 40 “unrelated” items was presented just once. The subjects were allowed to recall the items
in any order, and were given as much time and encouragement as necessary to obtain maximum retrieval on each recall attempt. Their verbal responses were tape-recorded so that the temporal course of retrieval could be documented by simple timing with a stopwatch. A week later the subjects were unexpectedly asked to attempt one more spontaneous retrieval of this list, to evaluate the stability of their organization. After the final delayed retrieval, forced-choice recognition was tested using distracters that were conceptually similar to the list items. The subjects were tested individually, and were paid for their participation. Each subject received only a single presentation of the list, at his or her own rate. A different kind of presentation was used for each subject. A conventional written presentation of the items was used for the first subject, who read the items aloud from 3 x 5 cards, at her own rate. The second subject received an unconventional presentation that requires phonetic processing (Cermak, Schorr, & Buschke, 1970) reading aloud the items which were typed backwards on cards. For example, she had to decode “hsif” into “fish.” The third subject received a “cognitive presentation” of each item, a description or a definition from which he had to infer what the item was. For example, after reading a card that said “Use this item twice a day to keep your teeth clean,” he responded “toothbrush.” The definitions used for the cognitive presentations and the 40-word list come from a different study by Erdelyi, Buschke, and Finkelstein (in preparation). The use of such cognitive presentations (Buschke, in press) tells us that the subject attended to each item, thought about each item, that each item was already in his permanent lexicon, and that each item was retrievable. In addition, the use of presentations which require the subject to name the item for himself right from the beginning starts off the learning process with a spontaneous retrieval from long-term storage. This seems like a good way to start, because the
a-20-75
iron dice comb bell feather bicycle bottle umbrella W” chair table
ma5 tree toaster fish heart chain hook flas can;l1e arrow glasses boat funnel football hat ladder television broom snail toothbrush hourglass scissors pineapple bat telephone book ;;E;rS
SINGLE 'RESENTATION
C.H.
20 21 22 23 24 25 26 27 28 29 30
13 14 15 16 17 18
2 3 4 5
1
funnel telephone television umbrella ladder hook bell iron book watch toothbrush comb pineapple feather hourglass glasses flaq
snake key table chair fish
FIG.
table bell
O:ll 0:15
B
4:Ol
0:54 0:58 1:05 1:09 1:14 1:lB 1:*2
I =I4:56
_
comb lwatch
boat bat football funnel umbrella OCtoDUS snaii fish telephone television chair table snake ladder bell feather pineapple
“““L
“..,” 3
0:~ O:*l
I 2:23 . 0
F 1;46 A .
SPONTANEOUS RETRIEVAL 2
*:39
:j:;
1,50 1:s
1:30 37 ii,,
I---bell fish snail
4
I
4 1:lO 1:14 1:19 1:*4 1:*9 1:34 1: 1:45 1:52 1:s *:07
ol;;
5
1, Spontaneous retrieval after a single written presentation of each item,
football snail octopus fish feather umbrella book television telephone flxl
noun tnnthhrllch comb bat
xmas tree toaster wm:;
o:oo u:o3 ",i;;
. . A
7
0
0:*3
WEEK LATER
316
HERMANBUSCHKE
greatest difficulty in selective retrieval from long-term storage during verbal learning (Buschke, in press) seems to be the initial spontaneousretrieval, after which subjectsare usually able to maintain retrieval quite well (Buschke, 1974, 1975). Presentations which require the subject to produce each item initially seem appropriate whenever there is any question about what the subject is doing with each item and whether the item is retrievable. RESULTS
Retrieval after Conventional Presentation Figure 1 shows the learning protocol of a young woman who repeated spontaneous retrieval after a single presentation of the 40 item list shown on the left. Each of the 40 items was typed on a 3 x 5 card, which she read aloud at her own rate, in the order shown. Each retrieval is shown in the order in which she retrieved the items. The temporal course of retrieval is shown by the time elapsedfrom the onset of retrieval, in minutes and seconds.The chunks are labeled by letters. Items that were retrieved individually, not as part of a cluster, are marked by black dots. The basicchunks denoted by the letters were identified by observing that those items appeared together in more than one retrieval attempt, and that such chunks were demarcated by different items or clusters on different retrieval attempts. For example, the items in cluster F (telephone and television) recur together on all retrievals, including delayed retrieval 1 week later. On Trial 1 F was demarcated by E and “umbrella,” on Trial 2 F was demarcated by “book” and “flag,” on Trial 3 by B and A, on Trial 4 by “pineapple” and “flag,” on Trial 5 by El and the end of retrieval, and on the delayed retrieval F was demarcated by K and E,. Therefore it seems reasonableto identify F asa basic well-defined chunk. While F seemsto represent a cognitive clustering of two semantically related items
that were separatedin the initial presentation, other chunks, such as E (football and funnel) appear to reflect chunking basedon proximity in the original sequential presentation. The chunks are relatively small. Some chunks increaseslightly asadditional items are added. For example, C (“Xmas tree” and “toaster”), which appears on Trials 1 and 2, isincreasedby the addition of “iron” on Trial 3 to form the larger cluster CZ, which also includes the new small cluster C, (“toaster” and “iron”) that recurs in the delayed retrieval a week later. Some new clusters arise on successive retrievals; these are marked by circled letters. For example, “bell” and “ladder” which were retrieved as individual items on Trial 1, appear together on Trial 2 as cluster I, which recurs on all subsequent retrievals. The number of individually recalled items, marked by black dots, decreasesover repeated retrievals. Somewhat fewer items were retrieved spontaneously 1 week later, but most of the items in delayed retrieval were still retrieved in the same clusters as before. Although items usually are part of just one chunk, at least in organization by adults, an item can be included in more than one chunk, and can alsobe retrieved alone despiteprevious chunking. Although clusters were sometimes demarcated by long pauses,such asthe pausesbefore and after cluster H (“hourglass” and “glasses”) on Trial 1, many clusters are not bounded by obvious pauses in retrieval. In general, it appears that more accurate identification of chunks in retrieval can be achieved by using the criteria describedthan by relying on pauses in retrieval, partly becausethe pausesbetween chunks become shorter as the chunks are organized. However, when longer retrieval pauses do occur, they can confirm the clustering shown by retrieval of items together on different retrieval attempts. It appears that spontaneous clustering of items into small, well-defined chunks, which also are organized, is a basic process in natural free recall learning. Thesebasic chunks
IDENTIFICATION
are stable and recurrent, and remain intact when they are associatedwith other chunks as higher-order organization develops; items in different juxtaposed chunks are not reorganized into new chunks. The higher-order organization of the chunks themselvesis demonst,ratedin Figure 2, which C.H.
FIG. 2. Organization of chunks in repeated retrieval after a single written presentation of each item.
shows the relative ordering of chunks in each retrieval, after removal of individually retrieved items (marked by black dots in Figure 1). Although Figure 2 shows that there was increasing organization of chunks over repeated retrieval attempts, the organization of chunks doesnot seemasextensive as the basic organization of individual items into recurrent clusters. Figure 2 also shows that most of the items retrieved in the delayed retrieval a week later were retrieved aspart of the samechunks asbefore, but the organization of chunks in the delayed retrieval was lessthan on Trials 4 and 5 a week before. Retrieval after Phonetic Processimg Figure 3 shows the repeated spontaneous retrieval of another young woman after a single presentation of the 40 item list shown on the left. Each item wastyped backwards on
a 3 x 5 card, so that shehad to sound out each word; for example, she had to decode “hsif” into “fish.” This unconventional kind of presentation (Cermak, Schnorr, & Buschke, 1970)presumably requires somephonetic pro-
OF CHUNKING
317
cessingand may interfere with rehearsal and cognitive processing. After she had sounded out each of the words at her own rate, she retrieved the items verbally in standard English. Her protocol also shows increasing organization by the formation of small recurrent clusters, with increasing organization of those clusters in later retrievals, and persistence of that organization in the final delayed retrieval a week later. Some of her chunks, such as B (“fish, ” “heart,” “chain,” “hook,” “flag”) are larger and reflect the serial ordering of those items in the initial presentation. Most of her chunks show a considerable amount of internal. organization, with preservation of the same sequential order of the items in a chunk. Some chunks, such as B on Trial 1 are demarcated by long pausesbefore and after. On Trial 2 the pausebetween chunks B and A is no longer extensive, although the pause between chunks B and C is still substantial. This subject showed the increasing rate of retrieval (Figure 7) which, along with increasing accuracy of retrieval, is one of the two major characteristics of verbal learning. It appearsthat someof the increasein her rate of recall may be accounted for by increasingly rapid retrieval of the items within a chunk and some may be accounted for by increasingly rapid transition from one chunk to another as higher-order organization of the chunks themselvesdevelops during learning. This protocol is compatible with the reasonable hypothesis that increasing rate of retrieval in verbal learning may be at least partly due to increasing chunking and organization of chunks in retrieval. Figure 4 shows her higher-order organization by ordering the clusters in retrieval, after deletion of individually retrieved items. As learning progressed, she was able to retrieve more chunks without interposition of individually retrieved items, and developed an extensive and persistent higher-order organization of the basic chunks formed during learning.
funnel football hat ladder television broom snail toothbrush hourglass scissors pineapple bat telephone book octopus watch iron dice comb bell feather bicycle bottle umbrella W" chair table key snake
boat
xmds tree toaster fish heart chain hook flag candle arrow glasses
SINGLE PRESENTATION
11 12 13 14 15 1C li I 1CI l! 3 2c ) 2: 1 2: I 2: 3 2. I 215 215 2' 1 218 2' 3 31D 31 32 33 34 35 36 37 38 39 40
ia
2 3 4 5 6 7 8 9
1
0:5R I:07 1:09 1:26 1:35 1:42
1:5! 3:oc 3:O' 3:12 3:lf 4:4; 5:3t 5:5; 8:2C 8:46 R:5f
1:s~
Spontaneous
. . . . . .
FIG.
I
H
G
F ;;:;
. .
*
",i",;
. r t
0%
ii:",
0:21 0:24 0:33
0:18
D
c
B
candle umbrella _ feather bell 1 adder bat key
3.
jJ 0:oo
H 0:03 0:13 0:lG
arrow 9 glfisses
-%?brush watch snail octopus pineapple snake bicycle table _ chair telephone book
Xmas tree toaster fish heart chain hook flag boat funnel football hat
1 l-
2:06 2:os
2:13 4:20
I .
o:57 1:ol
0:38 0~43 0~46 0~52
0~34
0~12 0:15
O:OB o:io
0~02 0~05
0~00
4
* ,, " . r c
B
A
key feather bell watch
boat funnel football 1 hat 1 ladder 1 broom 1 toothbrush
xmas tree toaster I fish hook chain heart flag
SPONTANEOUS
3
. 4:2E ,@ 5:04
L :i:':
1:3t
"
l
0:59
,,
l
",i;;
0:43
0:33
0:13 0:1-l 0:25 0!20
0:09 o:ll
0:02 0:07
P
book broom
L
F\
4
G
C
B
J,
I,
A
1:07
0~51
gun table
bell
1:51l
1:33
1:l I:22
I pin fea
L-iii
5
,- \
Xmas tree toaster
1 candle 0:07 glasses o:oe arrow 0~11 fish 0~13 heart 0~15 l-----d chain 0:lG flag O:IB hook 0~21s boat o:2e funnel 0~30 football 0:32 hat
o:os
0~00 0~02
pi”eap “J” feather key bat
chair tab!e
telephone-
7
umbkella gun
candle glasses arrow fish chain heart hook flag boat funnel football hat
Xmas tree toaster
1
0:oo
O:50 0:52 0:56
c
1
B
A
RETRIEVAL
I,
C
26 2;
14
1:15 1:2G
13
0:31
WEEK xmas tree toaster glasses candle arrow fish heart chain flag hook
0:09 0:12 0:lB
0:03 0:06
0:oo
N
z:;:,
snail octopus
J,
E
D
;I;:
ii:;
;f;;
0:59
0:52 0:55
;;y;;;;;'
0:51
m 1:03 I:07
C
0:23 B 0:25 0:26 0:31 0:3R 0:46
11
A
LATER
football hat toothbrush broom ladder watch
3 4 5 6 1 B 9 10 11 boat 12 funnel
:
0:29
Oil4 0:16 B 0:17 0:19 0:20 0:2G 0:27
;:;;
0:07
A 0:oo 0:03
retrieval after decoding a single presentation of each item written backwards.
watch glasses candle snake
Xmas tree toaster fish hook heart chain flag boat funnel football hat bell broom toothbrush ladder snail octopus
2
IDENTIFICATION
5
A '1 9 B C1 0 D M IO E3
6
319
OF CHUNKING
delayed retrieval a week later, he retrieved somewhat fewer items, more slowly. While this younger subject did show considerable clustering of individual elements which was still apparent in delayed retrieval a week later, Figure 6 shows very little higherorder organization of the clusters themselves.
J, F 4 p L 4 G
DISCUSSION
These individual protocols demonstrate directly that retrieval in natural free recall FIG. 4. Organization of chunks in repeated retrieval learning is organized by spontaneous clusterafter decoding a single presentation of each item written backwards. ing of items into small recurrent chunks that remain intact when the basic chunks are Retrieval after Cognitive Processing organized as learning proceeds. These protoFigure 5 shows repeated spontaneous re- cols provide typical illustrations of such trieval of this 40 item list by a 12-year-old boy, organizing by chunking, so the reader can after a single “cognitive presentation” by confirm that recurrent chunks can be identified means of descriptions or definitions from by finding clusters of items that appear which he inferred the items to be retrieved. For together in different retrievals and are demarexample, after he read the description “use cated by different items and chunks on different this item twice a day to keep your teeth clean,” retrievals. It appears that what happens in free recall he said “toothbrush.” This kind of cognitive presentation tells us that he attended to each learning is that the items are organized into item, thought about each item, that each item small stable chunks which also are organized. was in his permanent memory, and that he Because the basic chunks are directly apparent could retrieve each item. The use of such in retrieval, the actual organization of items cognitive presentations seems appropriate be- and chunks on each trial can be described and cause it provides these necessary assurances, the changes in organization during learning and seems interesting because cognitive pre- can be analyzed. This is shown clearly by sentations allow the experimenter to vary the spontaneous retrieval after a single presenkind of cognitive processing used at the time of tation, which is a special case of selective reminding and restricted reminding (Buschke, encoding (Buschke, in press). This lZyear-old boy retrieved nearly as 1973). The advantage of these paradigms is many items as the adults. In the forced-choice that they let subjects show what they have recognition test after the final delayed retrieval, learned by recall without presentation, which he recognized 39 of the 40 list items, like the shows true retrieval from long-term storage adult subjects who recognized 38 and 40 items. during learning, and permits organization of Figure 5 shows that he also organized the items retrieval without disruption by unnecessary into many recurrent chunks during learning. repeated presentation (Mandler & Dean, Some chunks, such as E (“funnel” and 1969). Free recall of unrelated items seems to “bottle”), appear to represent cognitive clus- be the appropriate way to determine whether tering on a semantic basis. Others, such as B items are normally cIustered into chunks that (“Xmas tree,” “chain,” “fish”), appear to be also are grouped in order to process large based more on proximity in sequential presen- amounts of information effectively. It seems tation than on conceptual relatedness. In appropriate to use some kind of selective
g-17-75 SPONiANEOUS
RETRIEVAL
FIG. 5. Spontaneous retrieval by a 12-year-old boy after inferring each item from its description
iron dice comb bell feather bicycle bottle umbrella gun chair telephone key snake
snail toothbrush hourglass scissors pineapple bat table book KtOl)"S
xms tree toaster fish heart chain hook flag candle arrow glasses boat funnel football hat ladder television
SINGLE IESENTATION
t&S. LATER
3
. . .
E
C
b
7:07 7:18 *:50 11:03 11:11
0:21 0:x 0:s 0:31 2:*9 3:43 x:50 4:19 4:22 495 5:oo 5:15
in a single cognitive presentation.
pineapple xmas tree chain snail television fish hook bat hat football watch hourglass bottle funnel candle key brorm
YEEK
IDENTIFICATION
FIG. 6. Organization of chunks in repeated retrieval by a lZyear-old boy after a single cognitive presentation.
reminding to minimize the disruptive effect of repeated presentation on the organization of retrieval; repeated retrieval after a single presentation is the kind of selective reminding that shows spontaneous organization of retrieval after the least possible presentation. The disadvantage of a singlesequentialpresentation is that organization may be limited becausesomeitems must be encoded before it is known what the rest of the items are, so that recoding may be necessary to group related items, and such grouping may be limited by the subject’s ability to remember related items that were presented earlier. In addition, the implicit constraint to avoid repetitions in order to recall as many different items as possiblein the necessarilysequential recall may prevent subjectsfrom showing that someitems may be part of several different chunks. Nonetheless, the individual protocols presentedhere clearly showthat retrieval in verbal learning is organized by clustering items into small recurrent chunks that remain intact when the chunks are grouped. These findings provide direct confirmation that retrieval is organized spontaneously by chunking even when subjects are not asked to order, group, or categorize the items in natural free recall. The analysis of organization shown here allows us to seethe actual chunks, and their organization, on each trial of learning. This lets us analyze organization in terms of the basic organization of items into chunks and the higher-order organization of the chunks. Since the actual composition of each chunk
OF CHUNKING
321
can be seen,the cognitive processinginvolved in the basic chunking and the grouping of chunks can be investigated. Analysis of chunking and grouping of chunks should help account for differences in rate of retrieval (Murdock & Okada, 1970) and for the increasing rate of retrieval during learning, as well as for the increasing number of items retrieved during learning. Figure 7 shows the increasing rate of retrieval of all items and of those items retrieved as part of a chunk on Trials 1, 2, 5 and 1 week later. Trials 3 and 4 were omitted for graphical clarity; Trial 2 is the first spontaneousretrieval without presentation. Initially there is a fast phase of recall, followed by a slow phaseas retrieval becomes more difficult. As learning proceeds,the rate of retrieval increases so that most of the items are retrieved in the fast phase. Although the rate of retrieval by the 12-year-old subject is slower than that of the adult subjects, it also increased over trials. A week later, the adults’ rate of retrieval was still nearly as high as on Trial 5, but the 12-year-old’s rate of retrieval was lower than it was on Trial 1. This may be related to organization by chunking and grouping of chunks during learning, since less of the 12-year-old’s total retrieval was due to chunked retrieval. The increasing rates and amounts of total and chunked retrieval in Figure 7 seemreasonably consistent with the chunking and higher-order organization of chunks shown in the preceding figures. The increase in rate of chunked retrieval, which may be due to increasing rate of retrieval of items in chunks as well as increasingly rapid retrieval of chunks, seemsto account for a substantial part of the increased rate of total retrieval. Identification of the actual chunks on each trial makes it possible to analyze rates of retrieval and changes in the rate of retrieval quite specifically in terms of the retrieval of individual items, the retrieval of items in chunks, and the retrieval of chunks, for example, in terms of time between individual items, time between items in chunks, and time
322
HERMAN
BUSCHKE
CH -ADULT
1.......1.‘...““‘,“,“,‘~‘.J I 3. 3’1567
1x3956789
,
I
3
4
5
6
7
P
9
lo
II
MJNUTES FIG. 7. Retrieval rate in repeated retrieval after a single presentation.
between chunks as learning proceeds. When extended recall is used, asit should in order to obtain the maximum retrieval necessary for accurate evaluation of learning (Buschke, 1973, 1974), it is necessary to analyze rate of retrieval, since, as Figure 7 illustrates, nearly the sametotal number of items may eventually be retrieved when enough time is provided for maximum retrieval at different rates. When extended recall is used, any correlation between organization and learning will be shown by correlation between organization and rate of retrieval, rather than number of items retrieved. Learning is generally shown by an increasing rate of retrieval, which presumably reflects ease of retrieval and eRecGvenessof encoding. Since it takes time to recall items sequentially, number of items recalled or probability of recall, which are customarily used to
measurelearning, really mean number of items recalled or probability of recall during some interval of time. Number of items recalled will depend on the amount of time allowed for recall; the number of items recalled in the standard brief recall period provides an estimate of the rate of retrieval during some fixed interval. Estimating the retrieval rate by the number of items recalled in a limited recall period may be useful when retrieval rate stays constant, but may be difficult when retrieval rate is not constant, since different estimates of learning could be obtained by using different recall periods. Since the constancy of recall rate and the appropriateness of any particular recall time can only be evaluated when retrieval rate over a longer period is analyzed first, and since extended recall should be used to obtain maximum retrieval on each trial, it seemsappropriate
IDENTIFICATION
to use extended recall and analyze retrieval rate more explicitly, including consideration of the effects of chunking and organization of chunks. Since it appears that natural free recall learning does involve spontaneous clustering of items into small recurrent chunks, such chunking should be taken into account when verbal learning is analyzed. Delineation of the basic chunks in learning, by identifying clusters of items that recur together in different retrievals and are demarcated by different items or chunks in different retrievals, should provide the information necessary for analyzing verbal learning in a way that takes the organization of retrieval into account. Analysis of verbal learning in terms of the basic chunking and the higher-order organization of chunks extends the analysis of “levels of processing” (Craik & Lockhart, 1972) to include levels of semantic processing, in retrieval and recoding as well as in initial encoding. Analysis of actual chunking should provide a more realistic basis for measurement of subjective organization during learning. The present findings indicate that it may not be appropriate to measure organization by counting the occurrence of n-tuples on Trials n and n + 1, since this ignores the fact that items are clustered in chunks of various sizes, some of which may persist throughout learning, while others may not. The simplest measure of organization is given by n - 1, where n is the number of items in a cluster. This measure provides the least possible discrimination between clusters of size n and n + 1, and between two clusters of n items and 1 cluster of 2n items. This measure can be interpreted as the minimum number of links needed to connect all of the items in a cluster. It is linearly related to the number of items in a cluster, and can include the higher-order grouping of basic chunks. The relative persistence of chunks can be taken into account by not counting the first occurrence of each chunk. It is conceivable that identification of re-
OF CHUNKING
323
current chunks might also be useful for analyzing some other kinds of organization. As the present findings suggest, it may not always be appropriate to assume, as some kinds of multidimensional scaling do (Fillenbaum & Rapoport, 1971; Shepard, Romney, & Nerlove, 1972; Romney, Shepard, & Nerlove, 1972), that every item in a set of items is necessarily related to every other item in that set, or that each item should be represented only once. For at least some sets of items, it seems more likely that some items may belong to more than one cluster but may not be related to all other items in the set (except trivially, because they are all members of the same general category). Also, in some cases items may be related only indirectly because the clusters to which they belong are related. In some experimental situations, all of the items may seem to be related even though every item may not actually be related to every other item. For example, the sequential retrieval of items in free recall has suggested that the organization of recall can be represented in terms of the proximity of each item to every other item. However, as the present findings suggest, it is possible that, while items are related to those other items that belong to the same chunks, items in different chunks may only appear to be related because the sequential nature of verbal recall results in an apparent ordering of items that may really be due to the necessarily sequential recall of different chunks. While it is certainly possible to represent the organization of a set of items as though every item were related to every other item in that set, even when they are not, it would seem more appropriate to determine experimentally whether every item is actually related to every other item or whether items are related only to some but not all of the other items in that set (and if so, what is related to what). When items are clustered in recurrent chunks, as in sorting experiments, for example, it would seem more appropriate to analyze their organization in terms of the
324
HERMAN
inclusion of items in specific chunks and organization of the chunks, than to ignore the experimentally obtained groupings in order to create a proximity matrix on the assumption that every item must be related to every other item. Analysis of chunking seems necessary to determine the actual organization and represent it most appropriately.
REFERENCES
BOUSFIELD,W. A. The occurrence of clusteringin the recall of randomly arranged associates. Journal of General
Psychology,
1953,49,229-240.
BOWER, G. H. Organizational
factors in memory. 1S-46. BUSCHKE, H. Selective reminding for analysis of memory and learning. Journal of Verbal Learning and Verbal Behavior, 1973,12,543-550. BUSCHKE, H. Spontaneous remembering after recall faihxe. Science, 1974,184,579-581. BUSCHKE, H. Retrieval of categorized items increases without guessing. Bulletin of the Psychonomic Society, 1975,5, 71-73. BUSCHKE,H. Retrieval in the development of learning. In N. J. Castellan, D. B. Pisoni, & G. R. Potts (Eds.), Cognitive Theory: Vol. ZZ. Hillsdale, New Jersey: Lawrence Erlbaum Associates, 1976. CERMAK, G., SCHNORR, J., & BUSCHKE, H. Word recognition as a function of speIIing direction during study and test. Psychonomic Science, 1970, 21, 127-128. COFER, C. N. Does conceptual organization influence the amount retained in immediate free recall? In Kleinmuntz, B. (Ed.), Concepts and the structure of memory. New York: John Wiley & Sons, 1967. CRAIK, F. I. M., & LOCKHART, R. S. Levels of processing : A framework for memory research. Cognitive
Journal
Psychology,
of Verbal
1970, 1,
Learning
and
Verbal
Behavior,
1972,11, 671-684. ERDELYI, M., BUSCHKE, H., & FINKELSTEIN, S. Spontaneous retrieval of words, pictures, and “Socratic presentations,” in preparation. FILLENBAUM, S., & RAPOPORT, A. Structures in the subjective lexicon. New York: Academic Press, 1971. JOHNSON,N. F. The role of chunking and organization in the process of recall. In G. H. Bower (Ed.), The psychology
of learning
and motivation.
York: Academic Press, 1970, Vol. 4.
New
BUSCHKE
KINTSCH, W., MILLER, R. F., & HOGAN, R. M. Semantic structure and clustering in free recall. Studies in mathematical learning theory and psycholinguistics, University of Colorado, 1970.
MANDLER, G. Words, lists, and categories. In J. L. Cohan (Ed.), Studies in thought and language. Tucson: University of Arizona Press, 1970. MANDLER, G. Organization and memory. In K. W. Spence & J. T. Spence (Eds.), The psychology of learning and motivation. New York: Academic Press, 1967, Vol. 1. MANDLER, G., & DEAN, P. J. Seriation: Development of serial order in free recall. Journal of Experimental Psychology, 1969,81,207-215. MARTIN, E., & NOREEN, D. L. Serial learning: Identification of subjective sequences. Cognitive Psychology, 1974,6,421-435. MILLER, G. A. The magical number seven, plus or minus two: Some limits in our capacity for processing information. Psychological Review, 1956, 63,81-97.
MURDOCK, B. B., JR., & OKADA, R. Interresponse times in single-trial free recall. Journal of Experimental Psychology, 1970,86,263-267. PELLEGRINO, J., & BATTIG, W. F. Relationships
higher order organizational recall. Journal of Experimental
among measures and free Psychology,
1974,
102,463-472.
POLLIO, H. R., KASSCHAU, R. A., & DENISE, H. E. Associative structure and the temporal characteristics of free recall. Journal of Experimental Psychology, 1968,76,190-197. POLLIO, H. R., RICHARDS, S., & LUCAS, R. Temporal properties of category recall. Journal of Verbal Learning and Verbal Behavior, 1969,8, 529-536. POLLIO, H. R. Composition of associative clusters. Journal of Experimental Psychology, 1964, 67, 199-208. ROMNEY, A. K., SHEPARD, R. N., & NERLOVE, S. B. (Eds.), Multidimensional scaling, Vol. ZZ: Applications. New York: Seminar Press, 1972. SHEPARD, R. N., ROMNEY, A. K., & NERLOVE, S. B. (Eds.), Multidimensional scaling, Vol. I: Theory. New York: Seminar Press, 1972. TULVING, E. Subjective organization in free recall of “unrelated” words. Psychological Review, 1962, 69,344-354.
TULVING, E., & DONALDSON, W. (Eds.), Organization of memory. New York: Academic Press, 1972. ZANGEN, M., ZIEGELBAUM, P., & BUSCHKE, H. Cluster: A program for identifying recurrent clusters. Behavior Research Methods for Znstrumentation, in press. (Received October 6, 1975)