Short-term memory items in repeated free recall

JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR

10, 190-193 (1971)

Short-Term Memory Items in Repeated Free Recall 1 MARION QUINN LEWIS Iowa State University, Ames, Iowa, 50010

Two-store models of memory interpret free recall serial position effects as outputs of two storage mechanisms, short-term memory (STM) and long-term memory(LTM). Recent items primarily represent STM output, and earlier items represent LTM output. In two free recall experiments, using written and oral recall, lists were presented for two immediately successive recalls. The typical free recall recency effect was observed in the first recall. In the second, recall of early items was nearly identical to Recall 1, but recall of recent items declined sharply. Results were interpreted as supporting two-store models of memory. lists for two recalls, one immediately after list presentation and the other after all lists had been recalled once. The Ss were asked to recall as m a n y words as possible from all lists in a "final recall." Although recent items were highest in immediate recall, they were lowest on the final recall. Atkinson and Shiffrin (1968) suggested that unrehearsed information in the "short-term store" decays within a very short time period, perhaps 15-30 sec. Waugh and N o r m a n ' s (1965) "echo box" analogy of STM also implies that STM has a quite limited duration, although Waugh and N o r m a n did not speculate about specific limits. In the present experiments, lists were also presented for two free recalls, but the second recall immediately followed the first (only 30 sec after list presentation) rather than after several minutes and presentation of additional lists. I f STM is as limited as these models suggest, then even the brief delay and activity of the first recall would exceed STM limits. Only L T M items would be available for the second recall. ~This research was supported by United States Therefore, recall of recent items should Public Health Service Research Grant MH 13192 decline sharply from first to second recall. from the National Institute of Mental Health to Wayne H. Bartz and conducted while the author was a EXPERIMENT I: WRITTEN RECALL recipient of a National Defense Education Act Title M e t h o d IV Graduate Fellowship. The author expresses Audio tape-recorded lists of 18 words having Thornappreciation to Robert A. Lewis for writing a listdike and Lorge A and AA ratings were presented at generating computer program. 190

Several two-store models of memory have been proposed, e.g., Atkinson and Shiffrin (1968), Glanzer and Cunitz (1966), and Waugh and N o r m a n (1965). In general, these models suggest that new information enters shortterm memory (STM) and is held there for processing into long-term memory (LTM). The capacity of STM is limited, and after STM is filled, new items enter by displacing old items. Rehearsal maintains items in STM, and unrehearsed information is rapidly lost. Recall and rehearsal are incompatible; rehearsal ceases when recall begins, resulting in rapid forgetting from STM. Under free recall, most recent items are reported first because recall activity interferes with holding items in STM. This " d u m p i n g " of STM items leads to the high recall of recent items characteristic of the free recall serial position curve. Thus, recent items primarily represent output of STM; earlier items recalled represent L T M output. Craik (1970) reported evidence interpreted to support such a position. He presented 10

REPEATED FREE RECALL 2-sec intervals for free recall. Four sets of such lists were prepared. The Ss were randomly assigned to list sets. The Ss were tested in small groups with written recalls. As Ss wrote, they covered each word with a card. The recall interval was 30 sec. Five practice lists (one recall only) preceded the 10 expermaental lists. Each experimental list was recalled twice, the second 30-sec recall interval immediately after the first. The Ss were 38 volunteers from introductory psychology classes at Iowa State University. Serial position effects were computed for both recalls. For analysis of variance, lists were divided into segments based on serial position: first (SPs 1-6), middle (SPs 7-12), and last (SPs 13-18). A 3 x 2 x 10 (Segments x Recalls x Lists) analysis of variance was conducted on Ss' recall scores.

Results Serial p o s i t i o n effects are shown in F i g u r e 1 f o r Recall 1 a n d Recall 2. Clearly, in Recall 1, the typical free-recall curve appears. T h e r e is a decline in Recall 2 only for recent 1terns.

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Fzo. 1. Serial position effects for Recall 1 and Recall 2, Experiment I (written recall). Recall 1 was greater t h a n R e c a l l 2, F(2,2220) = 51.78, p < .01. Serial p o s i t i o n effects were reflected in differences between segments, F(2,2220) = 66.45, p < .01 ; a n d the Recalls x Segments i n t e r a c t i o n was significant, F(2,2220) = 40.31, p < .01. I n Recall 2, first a n d m i d d l e segment recall was nearly identical to Recall 1, b u t last segment recall declined. T h e r e was a significant effect o f lists, F(9,2220) = 1.94, p < .05; a n d the Lists x Segments i n t e r a c t i o n was also significant, F(18,2220) = 2.65, p < .01. T h e fluctuations 8

191

a m o n g lists a n d segments d i d n o t suggest a clear t r e n d ; there was n6 consistent increase o r decrease in w o r d s recalled p e r list o r segment over the tenlists. I n t e r a c t i o n s o f Lists x Recalls a n d Lists x Recalls x Segments were n o t significant, F < 1.0. I t is possible t h a t a recall interval o f 30 sec m a y have been t o o s h o r t for written recall, p a r t i c u l a r l y for Ss w h o w r o t e slowly. Because recent items are typically r e p o r t e d first (Deese, 1957), Ss beginning Recall 1 with such items m a y have c o n t i n u e d the "first" recall o n Recall 2, t h a t is, r e p o r t i n g early items on Recall 2 t h a t they d i d n o t have e n o u g h time to write on Recall 1. A c c o r d i n g l y , E x p e r i m e n t I I was d o n e with oral recall. EXPERIMENT I I : ORAL RECALL

Method Lists of 18 words having Thorndlke and Lorge A and AA ratings were presented on a memory drum at a two-second rate. Order of list presentation was separately randomized for each S. The Ss were tested individually, with oral recalls. Otherwise, the procedure was the same as for Experiment I, five single-recall practice lists preceding 10 experimental lists. The Ss were 20 volunteers from introductory psychology classes at Iowa State University. Serial position effects were computed for both recalls. Again, for analysis of variance, hsts were divided into first, middle, and last serial position segments. A 3 × 2 x 10 (Segments × Recalls x Lists) analysis of variance was conducted on Ss' recall scores. Additionally, Recall 2 was examined as a function of item output position on Recall 1 for last-segment items and for combined first- and middle-segment ztems. The percentage of last and first-middle items at each output position was noted, and the correlation between output position and per cent of last-segment items at that position was computed.

Results Serial p o s i t i o n effects for each recall are shown in F i g u r e 2. A g a i n , on Recall 1, the typical free recall recency effect o b t a i n e d . O n Recall 2, recall o f early items was nearly identical to Recall 1, b u t recent item recall declined.

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lower Recall 2 percentages than items in later output positions. For first-middle items (input SPs 1-12), output order on Recall 1 had little relationship to Recall 2.

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Recall 2, Experiment II (oral recall). Recall was higher for Recall 1 than for Recall 2, F(1, 1140) = 24.72,p < .01. The effect of segments was significant, F(2, 1140)= 32.93, p < .01, reflecting serial position effects. The difference between recalls was specific to segments, F(2, 1140) = 19.87, p < .01 ; almost all the decline in Recall 2 occurred in the last segment. The effect of lists was not significant, F(9, 1140) < 1.0. There was a Lists × Segments interaction, F(18, 1140) = 1.81, p < .05. As in Experiment 1, however, there was no consistent increase or decrease in words recalled per segment over the ten hsts. Lists × Recalls and Lists × Recalls × Segments interactions were not significant, F < 1.0. On Recall 1, recent items tended to be reported first. At output positions 1 and 2, approximately 70 per cent of the items recalled were last-segment items. This percentage declined steadily later in recall: the correlation between output position and percentage of last-segment items at that position was r =

Results of these experiments indicate that although last-presented (STM) items were recalled better than earlier items on Recall 1, their level of recall declined on Recall 2. In contrast, early (LTM) items showed little forgetting between recalls. Results are compatible with those of Lewis and Bartz (1970), who repeated items on a second list as a function of serial position. Although recall of recent items was high on initial presentation, little learning was observed when these STM items were repeated. Large learning effects were observed for repeated LTM items. In Waugh and Norman's (1965) description of two-store memory, transfer or processing of information from STM to LTM is assumed to be independent of an item's serial position. That is, processing of information into LTM is considered relatively constant across serial positions. This formulation predicts a relatively flat recency effect for Recall 2. The results of both experiments support such an interpretation. The high recency effect on Recall 1 represents additional but impermanent recall of STM items. An alternative conception of STM-LTM transfer is described by Atkinson and Shiffrin IC0

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The relationship between output position on Recall 1 and percentage correct on Recall 2 is shown in Figure 3. (Output positions 10 and above were averaged because of their extremely small numbers. Few recent items were recalled in output positions later than 7, few early items later than 10; and output positions 13-18 were empty.) For last-segment items (input SPs 15-18), early Recall 1 output positions were associated with substantially

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REPEATED FREE RECALL

(1968). Transfer of information from STM to LTM is assumed to continue as long as the item remains in STM, i.e., there is a direct relationship between time in STM and amount of transfer to LTM. This formulation predicts a decline from first to second recall for recent items relative to earlier items because of their relatively shorter duration in STM before recall and the smaller resulting STM-LTM transfer. Craik (1970) reported such a "negative recency effect" on final recall, but the present results do not replicate this finding. Last-presented items tend to be reported first in free recall, and the present results show the typical "last-in, first-out" pattern. It might be argued that the decline between recalls for recent items was not due to STM loss but to the relatively longer delay between their recalls, interfering effects of recalling additional items during the delay and the more favorable rehearsal possibilities for items late in initial recall. Craik (1970) reported that items in early output positions on first recall appeared less often on final recall than items initially in late output positions. However, the present results show this negative relationship between early output position on Recall 1 and subsequent recall holds only for STM items. For LTM items, there is little relationship between output position on Recall 1, and subsequent recall. (Late output LTM items fare slightly better than early output items on Recall 2, but the overall

high recall of all LTM items limits early-late output differences.) Output position alone does not explain the decline in recall for STM items; LTM items in early output positions are not associated with low subsequent recall. In conclusion, the present findings are in accord with two-store memory interpretations which propose that high recall of recent items on Recall 1 is due to the dumping of items from a temporary STM. These items are then unavailable for an immediately subsequent recall. Earlier items, recalled from LTM, are available for later recall as is evident from their consistency at both recalls. REFERENCES

ATKINSON,R. C., & SIaIrFRIN,R. M. Human memory: A proposed system and its control processes. In K. W. Spence and J. T. Spence (Eds.), The psychology of learning and motivation. Vol. 2. New York: Academic Press, 1968. Pp. 89-195. CRAIIC,F. I. M. The fate of primary memory items in free recall. Journal of Verbal Learning and Verbal Behavior, 1970, 9, 143-148. DEESE, J. Serial organization in the recall of disconnected items. Psychological Reports, 1957, 3, 577-582. GLANZER,M., & Ct;NITZ,A. R. Two storage mechanisms in free recall. Journal of Verbal Learning and Verbal Behavior, 1966, 5, 351-360. LEWIS, M. Q., & BARTZ, W. H. Learning and the memory stores. Journal of Experimental Psychology, 1970, 86, 465-466. WAUGI~,N. C., & NORMAN,D. A. Primary memory. Psychological Review, 1965, 72, 89-•04. (Received October 1, 1970)