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Free recall curves: Nothing but rehearsing some items more or recalling them sooner?
JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR 14,
549-563 (1975)
Free Recall Curves: Nothing but Rehearsing Some Items More or Recalling Them Sooner? DELBERT A.
B R O D I E A N D L U B O M I R S. P R Y T U L A K
University of Western Ontario
The hypothesis that free recall curves reflecting the effects of serial position, presentation time, and delay of recall are attributable to subjects' pattern of rehearsal was explored in four experiments. In Experiment I, unrestricted overt rehearsal during list learning reveals that a list item's rehearsal time and item retention interval (the interval between an item's last rehearsal and the signal to begin recall) produced a multiple correlation of .86 with probability of recall. In Experiment II, subjects' spontaneous pattern of rehearsal was disrupted with instructions to either rehearse items equally, or else to selectively rehearse beginning, middle, or terminal items. Although free recall curves were grossly altered, the multiple correlation remained high (.89). Experiments III and IV show that better-thanpredicted recall of beginning items in certain conditions m the first two experiments is largely attributable to subjects' overt rehearsal underestimating concurrent covert rehearsal of beginning items. tasks: The more often an item is rehearsed, and the shorter its retention interval, the better it is recalled (Hellyer, 1962; Pollatsek, 1969). The hypothesis tested here is that the three free recall phenomena are a manifestation of the two short-term memory phenomena; that is, how long an item is rehearsed, the item's rehearsal time, together with the interval separating the last rehearsal of an item and the signal to begin recall, the item's item retention interval, determine that item's recall as effectively in multi-item, free recall tasks as they are presently known to do in singleitem, short-term memory tasks. The hypothesis that duration of rehearsal and time since last rehearsal can account for free recall is not entirely new. Several investigators have already suggested that rehearsal time can account for free recall of This research, which is part of the first author's beginning and middle items (Welch & Burnett, doctoral dissertation, was supported by a grant from 1924; Rundus & Atkinson, 1970; Rundus, the National Research Council of Canada. We thank 1971, 1974) and that item retention interval Ian Spence, Harry G. Murray, Allan U. Paivio, can account for free recall of terminal items William Siegel, Jane A. Siegel, John Gartrell, and (Robinson & Brown, 1926; Gruneberg, Robert S. Lockhart for helpful comments. Dr. Brodle is now at the University of Toronto, 1970; Glanzer, 1972, p. 159). The hypothesis that rehearsal time together with item retenToronto, Ontario, Canada M5S 1A1. Copyright © 1975 by Academic Press, Inc. 549 The data reported below attempt to demonstrate that five phenomena that are presently considered to be distinct are really only disguised manifestations of two underlying phenomena. Three of these phenomena are observed in multi-item, free recall tasks. First, immediate free recall decreases across early serial positions, remains low across middle positions, and rises across terminal positions (Murdock, 1962). Second, longer presentation times increase immediate free recall of beginning and middle items, but not terminal items (Murdock, 1962; Glanzer & Cunitz, 1966). And third, small delays in recall decrease free recall of terminal items, but not beginning and middle items (Postman & Philips, 1965; Glanzer, Gmnutsos, & Dubin, 1969). The remaining two phenomena are observed in single-item, short-term memory
All rights of reproducUon m any form reserved. Printed in Great Britain
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tlon interval can account for a number of basic free recall phenomena, however, has not been put forward. At the same time, empirical investigation has centered on rehearsal time (Rundus & Atkinson, 1970; Rundus, 1971) and has not examined item retention interval. Hence, previous experiments throw only a dim light on the explanatory power of rehearsal time combined with item retention interval. EXPERIMENT I
Serial position, presentation time, and delay of recall were varied in Experiment I. The question was, will the effects of these three variables on free recall be explainable through the mediation of rehearsal time and item retention interval ?
Method Subjects. Thirty-six introductory psychology students at the University of Western Ontario participated to fulfill a course requirement. Materials and apparatus. One-syllable nouns with a running frequency between 50 and 300 occurrences per million (both before and after the forms of each noun were combined using the procedure described by Thorndike and Lorge, 1944, p. ix) were selected randomly from Ku~era and Francis (1967). The nouns were assigned randomly to three practice lists and 12 experimental lists. Each list contained 18 nouns. The lists were presented on a memory drum at a rate of one noun every 1.25, 2.50, or 5.00 sec. The sound of the memory drum advancing and subjects' vocalizations were tape recorded. Procedure. Individual subjects were shown each list once, followed by a l-rain written free recall test. For each subject, the three practice lists were presented at different rates; on at least one practice list, recall was immediate; and on another practice list, recall was delayed for 15 sec. The experimental
lists were presented in six different random orders. Within each list order, presentation time and delay of recall were counterbalanced across trials within subjects, and across both trials and lists between subjects. At the start of the experiment, each subject was instructed that while the list was being presented, he should continually report which items he was thinking about. No restrictions were placed on the choice of list items to be rehearsed. At the start of each trial, subjects were told how fast the items would be presented. Following list presentation, subjects were asked to recall either immediately, or after counting backwards from a three digit number by threes for 15 sec.
Results As advocated by Myers (1972, pp. 176179), in all experiments, F ratios were evaluated using ultraconservative degrees of freedom for Fs which are clearly significant, and ultraliberal degrees of freedom for Fs which are clearly nonsignificant. Whenever these degrees of freedom failed to indicate unambiguously whether an F ratio was significant or not significant, the degrees of freedom were adjusted for the observed heterogeneity of variances and covariances. When the variances were heterogeneous, vertical bars in the graphs show + 1 standard error of each mean (vertical bars are omitted when the standard error lies inside the area encompassed by the plotted data point). When the variances were homogeneous, graphs show the average standard error of the mean. Recall. Recall data from experimental lists were analyzed by a 6 x 2 x 2 x 3 x 9 analysis of variance with list order (1 to 6) as a betweensubject factor, and delay (0 or 15 sec), trials (first or second), presentation time (1.25, 2.5, or 5 sec), and serial position (1 to 18 with two adjacent positions averaged) as within-subject factors. This analysis indicated that the main effects of delay, F(1, 30) --- 48.73, presentation time, F(1, 30) -- 58.52, and serial
FREE RECALL CURVES
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position, F(1, 30)=43.92, were significant 2.37, p > .05, all other Fs(4, 120)~< 1.72, (p < .01). These main effects were qualified p > .05. Hence, in spite of subjects' overt by three significant interactions: between rehearsal, the present recall data conform to serial position and delay, F(1, 30)= 23.59, previous covert-rehearsal findings. p < . 0 1 ; serial position and presentation Rehearsal. Rehearsal time and item retentime, F(7, 205)=2.25, p < .05; and delay tion interval data were analyzed with the and presentation time, F(2, 47) = 4.63, same analysis of variance used to analyze p < .05. recall data. Like analysis of recall, analysis The effects of serial position, delay, and of rehearsal time data indicated that the presentation time on recall are shown in main effects of serial position, F(1, 30)--Figure 1. Inspection of this figure indicates 115.67, and presentation time, F(1,30)-that the interaction between serial position 226,909.39, were significant (p < .01) as well and delay resulted from poorer recall of as the interaction between serial position and terminal items and unchanged recall of presentation time, F(1, 30) = 75.54. All other preterminal items when recall was delayed for main effects and interactions were non15 sec. Figure 1 also suggests that the inter- significant (p > .05). Inspection of Figure 2 action between serial position and presentation indicates that the interaction between serial time resulted from longer presentation times position and presentation time resulted from increasing recall of items in preterminal longer presentation times producing larger positions more than items in terminal posi- increases in rehearsal time for the first items tions. Finally, Figure 1 suggests that the in a list than for later items. interaction between delay and presentation Like analyses of rehearsal time and recall, time was attributable to a delay producing analysis of item retention interval data larger reductions in recall when items were revealed that the main effects of serial position, presented either every 1.25 or 2.50 sec than F(1, 30)=226.19, and presentation time, when items were presented every 5 sec. F(1, 30) = 646.50, were significant (p < .01), as Since previous investigators (Murdock, well as the interaction between serial position 1962; Glanzer & Cunitz, 1966; Raymond, and presentation time, F(1, 30) = 37.33. More1969) have found that longer presentation over, delay had a significant effect on item times increase recall of all items, except the retention interval, F(1, 30) = 6,228.26, p < .01 immediate recall of terminal items, separate (as it had on recall but not on rehearsal time). analyses of variance were conducted across The main effect of delay, however, resulted beginning (1 to 6), middle (7 to 12), and merely from a delay increasing each item's terminal (13 to 18) items at each delay to retention interval by 15 sec. All other main determine whether similar results were ob- effects and interactions were not significant tained in the present experiment. These (p > .05). Figure 3 shows that item retention analyses and inspection of Figure 1 indicate intervals decreased across all positions except that longer presentation times increased the first, and that increases in presentation delayed recall of terminal items, and both time increased item retention intervals for immediate and delayed recall of beginning early items more than later items. and middle items, all Fs(1, 30)/> 11.20, The relation between recall, rehearsal time, p < .01. As expected, however, presentation and item retention interval is shown in Figure time did not alter immediate recall of terminal 4. Each point in Figure 4 represents mean items, F < 1. Moreover, these main effects recall and either mean rehearsal time (left were not qualified by any interactions between panel) or mean item retention interval serial position and presentation time; for im- (right panel) for a given presentation time, mediate recall of terminal items, F(3, 101) = delay, and pair of adjacent serial positions.
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Specifically, the left panel shows the relation between rehearsal time and recall, after recall has been adjusted by subtracting recall that can be predicted by item retention interval. On the other hand, the right panel shows the relation between item retention interval and recall, after recall has been adjusted by subtracting recall that can be predicted by rehearsal time. 10
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Individually, neither rehearsal time (r = .47, p < .01) nor item retention interval (r = -.37, p < .01) is highly correlated with recall. Rehearsal time and item retention interval together, however, do better: The multiple correlation coefficient is .86 (p < .01), where
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mean recall = .25(log mean rehearsal time) .16(log mean item retention interval)+ .60. Plus and minus one standard error of the regression coefficients is _+.02 for both rehearsal time and item retention interval. As is to be expected, occasional marked deviations from the line of best fit occur. If there is any one condition for which deviations are consistently large, it is for the first pair of items in lists where items were presented every 1.25 sec. In each panel of Figure 4, data from this condition are represented by two triangles. One triangle in each panel represents immediate recall of the first two items in lists presented at a rate of one item every 1.25 sec, and the other triangle represents delayed recall of the same two items.
Discussion Experiment I replicates four phenomena already familiar to researchers in the area. First (Figure 4), recall is an increasing negatively accelerated function of rehearsal time, and a decreasing negatively accelerated function of item retention interval (Sanders, 1961; Hellyer, 1962; Pollatsek, 1969). Second (Figure 1), longer presentation times increase recall of all items except immediate free recall of terminal items (Murdock, 1962; Glanzer & Cunitz, 1966; Raymond, 1969). Third (Figure 1), small delays of recall decrease recall of items in terminal, but not preterminal positions (Postman & Phillips, 1965; Glanzer, Gianutsos, & Dubin, 1969). And fourth (Figure 2), at a long presentation time (5 see), rehearsal time is a decreasing negatively accelerated function of serial position (Rundus & Atkinson, 1970; Rundus, 1971), and as presentation time shortens to 2.50 and 1.25 see, rehearsal time approaches a ftat line. The central finding of Experiment I, however, is that the duration of rehearsal and time since last rehearsal can be viewed as the primary mechanism mediating the independent variables of serial position,
presentation time, and delay of recall, and the dependent variable of free recall. The most consistent deviation from this interpretation, moreover, was the incongruously good recall of the first two items in lists presented at the fastest rate. This incongrmty will be discussed further in Experiment IV. EXPERIMENT I I
One could explain the above results by assuming that while rehearsal is correlated with recall, it is not responsible for recall. That is, when items are presented slowly, subjects may choose to rehearse the items that they have already learned, so rehearsal follows learning and is neither learning itself, nor a contemporaneous manifestation of learning. Experiment II attempted to test this hypothesis by manipulating which items subjects rehearsed. If learning precedes rehearsal, or is independent of rehearsal, then changing the subject's rehearsal pattern should have little effect on recall curves and should impair rehearsal's ability to predict recall. If, on the other hand, altered rehearsal produces radical changes in recall even while rehearsal continues to predict recall then the tenability of the hypothesis that rehearsal plays a causal role in recall will be strengthened.
Metkod Subjects. Forty-eight introductory psychology students at the University of Western Ontario participated to fulfill a course requirement. None of these subjects had participated in Experiment I. Materials and apparatus. The materials and apparatus were the same as in Experiment I except that four practice and eight experimental lists were presented, and on every list a 6-mm line extended across the memory drum paper between the sixth and seventh items and between the twelfth and thirteenth items.
FREE RECALL CURVES
Procedure. Each subject was shown the 12 lists at the rate of one item every 5 sec. Before each list, the subject was told which of four rehearsal patterns to use; he used each pattern once on the four practice lists and twice on the eight experimental lists. The rehearsal patterns were as follows. In the Equal condition, subjects were told to think about each item only while it was being presented. In the remaining three conditions, subjects were told to think about the beginning items while the beginning items were being presented, but with different patterns being required for later items. In the Beginning condition, subjects were asked to spend half their time thinking about beginning, and half thinking about middle items, while middle items were being presented; and half their time thinking about beginning, and half about terminal items, while terminal items were being presented. In the Middle condition, subjects were told to think only about middle items while middle items were being presented, and to spend half their time thinking about middle items, and half about terminal items, while terminal items were being presented. Finally, in the Terminal condition, subjects were told to think about both beginning and middle items while middle items were being presented, but to think only about terminal items while terminal items were being presented. For each subject, the rehearsal instructions were counterbalanced across trials; and within groups of four subjects, the rehearsal instructions were counterbalanced across trials and lists. Each group of four subjects saw the experimental lists presented in a different random order. Each subject was instructed to continually report during list presentation which list items he was thinking about. Following presentation of each list, subjects were given a 1-min written free recall test on that list. For half the subjects, recall was immediate, whereas for the other half, recall was delayed for 15 sec of counting backwards by threes
555
from a three-digit number. After all lists had been presented, each subject was questioned to determine if he had violated the covert rehearsal instructions.
Results Recall. The recall data were analyzed with a 6 x 2 x 2 x 4 x 9 analysis of variance with list order (1 to 6) and delay (0 to 15 sec) as between-subject factors; and trials (first or second), rehearsal pattern (Equal, Beginning, Middle, or Terminal), and serial position (1 to 18 with two adjacent positions averaged) as within-subject factors. This analysis revealed that the main effects of delay, F(1, 36) = 9.91, rehearsal pattern, F(1, 36) = 13.54, and serial position, F(1, 36)= 67.63, were significant (p < .01). These main effects were qualified by two significant (p < .01) interactions: between serial position and delay, F(1, 36) = 19.48, and between serial position and rehearsal pattern, F(1, 36)= 23.50. All other main effects and interactions were nonsignificant (p > .05). Like recall data in Figure 1, recall data in Figure 5 indicate that the interaction between serial position and delay resulted from poorer recall of terminal items and unchanged recall of preterminal items when recall was delayed for 15 sec. Figure 5 also indicates that within the portion of the list after which the rehearsal pattern was named, recall was raised unevenly, with the first items in the portion receiving the largest increase in recall. As a result, compared to the slope in the Equal condition, the slope across beginning items in the Beginning condition became more negative, the slope across middle items in the Middle condition changed from zero to negative, and the slope across terminal items in the Terminal condition changed from positive to close to zero in the I condition and negative in the D condition. More briefly, these changes in recall can be summarized as the exaggeration, or the production, of local primacy effects in the list portion selected for increased rehearsal.
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FIO. 5. Proportion of items recalled in Experiment II as a function of serial position and rehearsal pattern (Equal, Beginning, Middle, or Terminal) when recall was either immediate (I) or delayed (D). The confidence interval on the upper right encloses+ 1 standard error of each mean. Rehearsal. Rehearsal time and item retention interval data were analyzed with the same analysis of variance used to analyze recall data. Like analysis of recall data, analysis of rehearsal time data indicated that the main effect of serial position, F(1, 36)= 522.93, and the interaction between serial position and rehearsal pattern, F(1, 36)=226.48, were significant (p < .01). All other main effects and interactions were not significant (p > .05). Inspection of Figure 6 indicates that the interaction between serial position and rehearsal pattern resulted from all rehearsal patterns except Equal producing a sharp negative slope in rehearsal time across beginning positions, and from Middle and Terminal rehearsal patterns producing a sharp negative slope in rehearsal time across middle and terminal positions, respectively. Like analyses of rehearsal time and recall data, analysis of item retention interval data
indicated that the main effect of serial position, F(1, 36)= 1,566.65, and the interaction between serial position and rehearsal pattern, F(1, 36)= 172.95, were significant (p <.01). Moreover, like recall, but unlike rehearsal time, the main effects of rehearsal pattern, F(1, 36)=698.09, and delay, /7(1, 36)= 1,162.22, were significant (p<.01). The main effect of delay resulted from a delay increasing each item's item retention interval by 15 sec. All other main effects and interactions were not significant (p > .05). As can be seen in Figure 7, the interaction between serial position and rehearsal pattern resulted from the rehearsal patterns shortening the item retention intervals in the list fractions after which the rehearsal patterns were named, and rotating the slopes counterclockwise so as to make them positive (across beginning items in Beginning and Terminal conditions and across middle items in the
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FIG. 6. Mean rehearsal time in seconds (Experiment II) as a function of serial position and rehearsal pattern (Beginning, Middle, Terminal, or Equal). To avoid crowding, the line representing the Beginning rehearsal pattern is displaced shghtly to the right, and the line representing the Terminal rehearsal pattern to the left. Confidence intervals enclose + 1 standard error of each mean.
Middle condition), zero (across beginning items in the Middle condition), or less strongly negative (across terminal items in the Terminal condition). The relation between recall, rehearsal time, and item retention interval is illustrated in Figure 8. Each point in Figure 8 represents mean recall and either mean rehearsal time
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FIG. 7. Mean item retention interval in seconds (Expernnent II) as a function of serial position and rehearsal pattern (Equal, Middle, Terminal, or Beginning). To avoid crowding, the line representing the Terminal rehearsal pattern is displaced slightly to the right, and the line representing the Beginning rehearsal pattern to the left. Confidence intervals enclose + 1 standard error of each mean.
(left panel) or mean item retention interval (right panel) for a given rehearsal pattern, delay, and pair of adjacent serial positions. Specifically, as in Figure 4, the left panel in Figure 8 shows the relation between rehearsal time and recall, after recall has been adjusted
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by subtracting recall that can be predicted by continue to be highly correlated when item retention interval; and the right panel subjects are required to alter their usual shows the relation between item retention rehearsal pattern. Moreover, inspection of interval and recall, after recall has been Figures 4 and 8, as well as comparison of the adjusted by subtracting recall that can be regression coefficients obtained in Experipredicted by rehearsal time. ments I and II, indicate that manipulating a Individually, neither rehearsal time (r =.64, subject's rehearsal has little or no effect on p < .01) nor item retention interval (r = -.47, the slope of the rehearsal time and item p < . 0 1 ) is highly correlated with recall. retention interval regression curves. These Rehearsal time and item retention interval findings encourage the supposition that together, however, do better: The multiple changes in rehearsal are responsible for correlation coefficient is .89 (p < .01), where changes in recall, not only when subjects mean recall = .28(Iog mean rehearsal time) are free to rehearse whichever items they .15(log mean item retention interval)+ .50. choose, but also when they are required to Plus and minus one standard error of the follow a prespecified pattern of rehearsal. regression coefficients is _+.02 for rehearsal As in Experiment I, most of the effects of time and _+.01 for item retention interval. serial position on recall in the present experiif, as in Experiment I, we search for the ment can be predicted from changes in conditions with consistently large deviations rehearsal time and item retention interval. from the line of best fit, we find that they are Nevertheless, one finding is particularly immediate and delayed recall of the first troublesome--namely, a primacy effect in pair of items in the Equal condition (repre- the Equal condition where subjects were sented by triangles in Figure 8) and in the instructed to rehearse each item only while it Terminal condition (represented by squares). was being presented (see Figure 5). Other Perhaps rehearsal time and item retention investigators have also obtained primacy interval data failed to predict some changes effects using similar instructions (Glanzer & in recall because subjects covertly disobeyed Meinzer, 1967; Leicht, 1968; Fischler, Runthe rehearsal instructions. Despite almost dus, & Atkinson, 1970). If subjects do obey perfect compliance with instructions to limit their rehearsal instructions, then these findovert rehearsals to specific items, at the end ings would suggest that duration of rehearsal of the experiment most subjects reported and time since last rehearsal are not the sole that they had violated instructions to limit determinants of the primacy effect. In fact, their covert rehearsals to specific items. however, subjects admit disobeying rehearsal That is, 36 of the 48 subjects tested reported instructions when rehearsal is covert (Welch that: (a) in the equal condition, they covertly & Burnett, 1924; Leicht, 1968). Until now, rehearsed beginning items while later items however, overt rehearsal has been accepted were being presented; (b) In the middle as an accurate reflection of covert rehearsal, condition, they covertly rehearsed beginning and the possibility that subjects overtly items while either middle or terminal items obey rehearsal instructions while covertly were being presented; and (c) In the terminal disobeying them has not been investigated. condition, they covertly rehearsed beginning The discrepancy between overt and covert or middle items while terminal items were rehearsal is examined in Experiments III and being presented. IV. Discussion
The results from the present experiment clearly indicate that rehearsal and recall
EXPERIMENTIII Perhaps subjects in Experiment II disobeyed instructions to covertly rehearse each
FREE RECALL CURVES
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item only while it was being presented because when learning other lists, they were required to overtly rehearse the first items while later items were being presented. Alternatwely, perhaps subjects became confused at the end of the experiment and incorrectly reported that they had covertly rehearsed earlier items while later items were being presented. Experiment III was conducted to get subjects to obey equal rehearsal instructions, and to obtain more accurate and precise information on which items subjects covertly rehearse when learning under equal rehearsal instructions. This was attempted by having subjects participate in only one condition, and by having subjects indicate, after concurrent overt rehearsal, which items they had usually rehearsed aloud, as well as which items they had rehearsed covertly during list presentation. If subjects can accurately report which items they rehearsed aloud, then we can be more confident that they will also be able to accurately report which items they rehearsed covertly. Moreover, if the measure of covert rehearsal time for the first items in a list is longer, or covert item retention interval is shorter, than suggested by overt rehearsal (whether measured by concurrent vocalization or later reproduction) then we will have reason to suppose that rehearsal is responsible for the primacy effect even when subjects are required to restrict their overt rehearsal to the item being presented.
Each subject was instructed to continuously articulate the list words that he was thinking about while the list was being presented, to think about each item only while it was being presented, and to obey the rehearsal instructions, even if obeying the instructions reduced the number of items he could learn and recall. Immediately following list presentation, subjects were given a l-rain written free recall test on that list. Following recall of the sixth list, subjects were given a rehearsal reproduction sheet. Half the subjects were instructed first to use numbers to indicate as closely as possible which word or words they usually said aloud while each word was being presented during the last four lists. As examples on how to fill out this sheet, each subject was told to put a 1 next to word 1 if he had usually said the first word while it was being presented, and to put either 2, 1, or 1 and 2 next to word 2 depending on whether he had usually said only word 2, only word 1, or both words 1 and 2 while the second word was being presented. After each subject had indicated which words he had usually said, he was handed another rehearsal reproduction sheet, and the earlier instructions were repeated with the words "thought about" inserted for the words "said aloud." The other half of the subjects first indicated which words they usually thought about, then which words they usually said aloud.
Method Subjects. The subjects were 24 University of Western Ontario introductory psychology students who had not participated in either Experiment I or II.
Results
Materials and apparatus. The materials and apparatus were the same as those used in Experiment I, except for the addition of rehearsal reproduction sheets with "word 1" to "word 18" printed in a vertical column. Procedure. Individual subjects were shown two practice and four experimental lists presented at a rate of one item every 5 see.
Recall. Recall data were analyzed by a 4 x 9 analysis of variance with trials (1 to 4) and serial position (1 to 18 with two adjacent positions averaged) as within-subject factors. Only the main effect of serial position, F(1, 23)=26.29, was significant (p <.01). The effect of serial position on recall was essentially the same as that shown in Figure 5 for immediate recall in the Equal condition. That is, the probability of recall in the present experiment decreased from .57 to .36 across beginning positions, remained fairly constant
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at .34 across middle positions, and increased to .91 across terminal positions. Rehearsal All subjects vocalized each item only while it was being presented, and after all lists had been presented they correctly reported that they had vocalized each item only while it was being presented. However, even though each subject was instructed to also covertly rehearse each item only while it was being presented, all subjects reported disobeying the covert rehearsal instructions. Specifically, each subject reported from 3 to 44 covert violations per list (that is, covertly rehearsing earlier items while later items were being presented). Moreover, half the subjects reported over 11 violations per list, and the mean number of violations per subject per list was 14.8 with a standard deviation of 11. Rehearsal time and item retention interval data from subjects' reproductions of their covert rehearsal were analyzed with serial position (1 to 18 with two adjacent positions averaged) as the only within-subject factor. These analyses revealed significant (p < .01) effects of serial position on both rehearsal time, F(1, 23)--15.01, and item retention interval, F(1, 23)= 123.25. Serial position decreased rehearsal time from 7.36 sec for the first items to between 4 and 5 sec for later items. Similarly, serial position decreased item retention intervals from 63.25 sec for the first items to 1.96 sec for the last items. Rehearsal time and item retention interval data from subjects' concurrent overt rehearsals and from subjects' reproductions of their overt rehearsals could not be analyzed because neither measure varied between subjects. That is, rehearsal time for each item in the list was always 5 sec, and item retention intervals always decreased linearly from 82.50 for the first items to 2.50 sec for the last items.
Discussion As in Experiment II, the present results indicate that requiring subjects to continu-
ously vocalize only the item being presented does not ensure that they will obey instructions to avoid covertly rehearsing earlier items. Moreover, unlike Experiment II, the present results show that subjects' overt rehearsal selectively underestimates rehearsal time and overestimates item retention interval for beginning items. As a result, overt rehearsal predicts lower recall for beginning items than is in fact observed. Recomputing rehearsal time and item retention interval for the first two items in the Equal condition in Experiment II (by adding the difference between reproduction-covert and either reproduction-overt or concurrent-overt to rehearsal time and item retention interval) has the effect of reducing the discrepancy between predicted and observed recall by about two-thirds. Hence, the present results provide additional evidence that serial position alters recall through the mediation of rehearsal, even when subjects are instructed to rehearse each item only while it is being presented. EXPERIMENTIV Perhaps like the discrepancy between rehearsal and recall in the Equal condition in Experiment II, the discrepancy observed in Experiment I when items were presented quickly resulted from subjects selectively failing to report all rehearsals of the first words in a list. As in Experiment III, this possibility was tested in the present experiment by having subjects indicate, after concurrent overt rehearsal, which items they had rehearsed aloud, as well as which items they had rehearsed covertly during list presentation.
Method The subjects were 24 University of Western Ontario introductory psychology students who had not participated in any of the previous experiments. The materials, apparatus, and procedure were the same as those used in Experiment II, except lists were presented at a
561
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rate of one item every 1.25 sec and no restrictions were placed on the choice of list items to be rehearsed. Results Recall. Analyzing recall with the analysis of variance specified in Experiment III indicated that only the main effect of serial position, F(1, 23)=55.52, was significant (p < .01). The effect of serial position on recall was essentially the same as that shown in Figure 1 for immediate recall when items were presented for 1.25 sec. That is, the probability of recall in the present experiment decreased from .56 to .18 across beginning positions, remained fairly constant at .22 across middle positions, and increased to .90 across terminal positions. Rehearsal. The concurrent-overt rehearsal and rehearsal reproduction data were analyzed by 3 x 9 analyses of variance with report of rehearsal (concurrent-overt, reproductionovert, or reproduction-covert) and serial position (1 to 18 with two adjacent positions averaged) as within-subject factors. Analyses of rehearsal time and item retention interval data indicated that the main effects of serial position, both Fs(1, 23)/> 10.29, p < .01, and report of rehearsal, both Fs(1, 28)/> 6.99, p < .05, were significant. On the other hand, neither interaction between serial position and report of rehearsal was significant, both Fs(2, 34) ~<2.51, p > .05. Since it was expected that differences in rehearsal time and item retention interval as a function of different methods of reporting rehearsal would be limited to the first serial positions, separate analyses of variance were conducted across beginning, middle, and terminal positions. As expected, these analyses indicated that the main effect of report of rehearsal was significant for rehearsal time, F(2, 38)= 6.46, p < .01, and item retention interval, F(1, 31)=6.14, p < . 0 5 , across beginning positions, but not across middle or terminal positions, all Fs(2, 46)42.14, p > .05. The main effects of report of rehearsal
across beginning positions were due to concurrent-overt and reproduction-overt measures yielding lower estimates of rehearsal time (1.72 and 1.83 sec) and higher estimates of item retention interval (18.06 and 18.18 sec) for the first two items in a list than those obtained with a reproduction-covert measure (rehearsal time, 2.21 sec; item retention interval, 15.95 sec). Discussion
Like Experiment III, the present results suggest that estimating overt rehearsal time and item retention interval from subjects" reproduction of their overt rehearsals gives results almost identical to those obtained from subjects' concurrent overt rehearsal. Subjects' ability to reproduce their overt rehearsals encourages the belief that they could also accurately reproduce their covert rehearsals. Comparisons of the reproduction-covert data with both the concurrent-overt and reproduction-overt data indicates that the latter measures underestimate rehearsal time and overestimate item retention intervals for the first two items. Increasing rehearsal time and reducing item retention intervals by the difference between reproductioncovert and concurrent-overt conditions would reduce by about one-third the discrepancy between predicted and observed recall of the first two items in lists presented quickly in Experiment I. Hence, although these points would still deviate from the regression curves, their deviation would be less striking. Consequently, the present results lend further support to the hypothesis that rehearsal does in fact produce the primacy effect even when items are presented quickly. GENERAL DISCUSSION
The results from the present series of experiments support the hypothesis that serial position, delay, and presentation time alter free recall by first altering rehearsal time and item retention interval. That is,
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immediate free recall is a U-shaped function of serial position (Figure 1) because subjects rehearse beginning items more (Figure 2) and terminal items later (Figure 3) than middle items. The increases in item retention intervals, produced by increasing delay of recall, lower recall of terminal items only (Figure 1) because extending item retention intervals has more effect (Figures 4 and 8) on items with short item retention intervals (terminal items, Figure 3) than on items with alreadylong item retention intervals (beginning and middle items, Figure 3). Finally, longer presentation times increase immediate free recall of beginning and middle items only (Figure 1) because of an increased rehearsal time (Figure 2) which is not offset by a concomitant increase in an already-long item retention interval (Figures 3 and 4). Like beginning and middle items, immediate free recall of terminal items varies with changes in rehearsal (Figure 5). Increased rehearsal time at longer presentation times (Figure 2), however, does not increase immediate free recall of terminal items (Figure 1) because it is neutralized by the potent increase in short item retention intervals (Figure 3). The finding that rehearsal can account for the effects of serial position, delay of recall, and presentation time on free recall encourages the supposition that rehearsal can also account for the effects of several other manipulations. This supposition is supported by previous research (Rundus, 1971) that indicates that when no restrictions are placed on rehearsal, rehearsal accurately predicts spacing and isolation effects in free recall. Whether spacing and isolation effects can be eliminated by having subjects rehearse each item only while it is being presented is not known. The present results, however, suggest that subjects will disobey equal-rehearsal instructions. Hence, any tests of the relation between rehearsal and recall must rely on more than the investigator's instructions and the subjects' concurrent overt rehearsals.
Instead, as demonstrated by Reitman's (1971, 1974) reversed conclusion concerning the presence of rehearsal during a signal-detection task, before dismissing rehearsal as an explanation it is necessary to verify the accuracy of the measure of rehearsal being used.
REFERENCES FISCHLER, I., RUNDUS,D , & ATKINSON,R. C. Effects
of overt rehearsal procedures on free recall. Psychonomic Science, 1970, 19, 249-250.
GLANZER,M. Storage mechanisms in recall. In G. H. Bower (Ed.), The psychology of learning and mottvation: Advances m research and theory.
New York: Academic Press, 1972. Vol. 5. Pp. 129-193. GLANZER, IV[., & CUNITZ, .A.R. Two storage mechanisms in free recall. Journal of Verbal Learning and
Verbal Behavior, 1966, 5, 351-360. GLANZER, M, GIANtrTSOS, R., & DUBIN, S. The removal of items from short-term storage. Journal of Verbal Learning and Verbal Behavior,
1969, 8, 435-447. GLANZER,M., & MEINZER,A. The effects of lntralist activity on free recall. Journal of Verbal Learning and Verbal Behavior, 1967, 6, 928-935 GRUNEBERG,M. M. A dichotomous theory of memory unproved and unprovable? Acta Psyehologiea, 1970, 34, 489-496. HELLYER,S Frequency of stimulus presentation and short-term decrement in recall. Journal of ExperimentalPsyehology, 1962, 64, 650 KU6ERA, H., & FRANCIS, W. N. Computational analysis of present-day American English. Providence, RI' Brown Umverslty Press, 1967 LEICnT, K. L. Dafferential rehearsal and primacy effects Journal of Verbal Learning and Verbal Behavior, 1968, 7, 1115-1117. MURDOCK,B. B., JR. The serial position effect in free recall. Journal of Experimental Psychology, 1962, 64, 482-488 MYERS, J. L. Fundamentals of experimental design. Boston' Allyn and Bacon, 1972. 2nd ed. POLLATSEK,A. Rehearsal, interference, and spacing of practice in short-term memory Technical Report, Human Performance Center, University of Michigan, 1969. C~tedby Bjork, R. A., Repetition and rehearsal mechanisms in models for short-term memory. In D. A. Norman (Ed.), Models of human memory. New York" Academic Press, 1970. P. 325.
FREE RECALL CURVES
POSTMAN,L., & PHILLIPS,L. W. Short-term temporal changes in free recall. Quarterly Journal of ExperimentalPsychology, 1965, 17, 132-138. RAYMOND, B. Short-term storage and long-term storage in free recall. Journal of VerbalLearning and VerbalBehavior, 1969, 8, 567-574. ROBINSON, E. S., t~ BROWN, M. A. Effect of serial position upon memorization. American Journal of Psychology, 1926, 37, 538-552. REITMAN, J. S. Mechanisms of forgetting in shortterm memory. Cognitive Psychology, 1971, 2, 185-195. REITMAN, J. S. Without surreptitious rehearsal, information in short-term memory decays.
Journal of Verbal Learning and Verbal Behavior, 1974, 13, 365-377. Ru~,aJus, D. Analysis of rehearsal processes in free recall. Journal of Experimental Psychology, 1971, 89, 63-77.
563
RLrNDtrS, D. Output order and rehearsal in multi-trial free recall. Journal of VerbalLearning and Verbal Behavior, 1974, 13, 656-663. RUNDUS,D., & ATKINSON,R. C. Rehearsal processes in free recall: A procedure for direct observation.
Journal of Verbal Learning and Verbal Behavior, 1970, 9, 99-105. SAr,rDERS, A. F. Rehearsal and recall in immediate memory. Ergonomtcs, 1961, 4, 29-34. THORNDIKE, E. L., & LORGE, I. The teacher's word book of 30,000 words. New York: Columbia University Press, 1944. WELCH,G. B., & BURNETT,C. T. Is primacy a factor in association-formation? American Journal of Psychology, 1924, 35, 396-401.
(Received May 19, 1975)
549-563 (1975)
Free Recall Curves: Nothing but Rehearsing Some Items More or Recalling Them Sooner? DELBERT A.
B R O D I E A N D L U B O M I R S. P R Y T U L A K
University of Western Ontario
The hypothesis that free recall curves reflecting the effects of serial position, presentation time, and delay of recall are attributable to subjects' pattern of rehearsal was explored in four experiments. In Experiment I, unrestricted overt rehearsal during list learning reveals that a list item's rehearsal time and item retention interval (the interval between an item's last rehearsal and the signal to begin recall) produced a multiple correlation of .86 with probability of recall. In Experiment II, subjects' spontaneous pattern of rehearsal was disrupted with instructions to either rehearse items equally, or else to selectively rehearse beginning, middle, or terminal items. Although free recall curves were grossly altered, the multiple correlation remained high (.89). Experiments III and IV show that better-thanpredicted recall of beginning items in certain conditions m the first two experiments is largely attributable to subjects' overt rehearsal underestimating concurrent covert rehearsal of beginning items. tasks: The more often an item is rehearsed, and the shorter its retention interval, the better it is recalled (Hellyer, 1962; Pollatsek, 1969). The hypothesis tested here is that the three free recall phenomena are a manifestation of the two short-term memory phenomena; that is, how long an item is rehearsed, the item's rehearsal time, together with the interval separating the last rehearsal of an item and the signal to begin recall, the item's item retention interval, determine that item's recall as effectively in multi-item, free recall tasks as they are presently known to do in singleitem, short-term memory tasks. The hypothesis that duration of rehearsal and time since last rehearsal can account for free recall is not entirely new. Several investigators have already suggested that rehearsal time can account for free recall of This research, which is part of the first author's beginning and middle items (Welch & Burnett, doctoral dissertation, was supported by a grant from 1924; Rundus & Atkinson, 1970; Rundus, the National Research Council of Canada. We thank 1971, 1974) and that item retention interval Ian Spence, Harry G. Murray, Allan U. Paivio, can account for free recall of terminal items William Siegel, Jane A. Siegel, John Gartrell, and (Robinson & Brown, 1926; Gruneberg, Robert S. Lockhart for helpful comments. Dr. Brodle is now at the University of Toronto, 1970; Glanzer, 1972, p. 159). The hypothesis that rehearsal time together with item retenToronto, Ontario, Canada M5S 1A1. Copyright © 1975 by Academic Press, Inc. 549 The data reported below attempt to demonstrate that five phenomena that are presently considered to be distinct are really only disguised manifestations of two underlying phenomena. Three of these phenomena are observed in multi-item, free recall tasks. First, immediate free recall decreases across early serial positions, remains low across middle positions, and rises across terminal positions (Murdock, 1962). Second, longer presentation times increase immediate free recall of beginning and middle items, but not terminal items (Murdock, 1962; Glanzer & Cunitz, 1966). And third, small delays in recall decrease free recall of terminal items, but not beginning and middle items (Postman & Philips, 1965; Glanzer, Gmnutsos, & Dubin, 1969). The remaining two phenomena are observed in single-item, short-term memory
All rights of reproducUon m any form reserved. Printed in Great Britain
550
BRODIE AND PRYTULAK
tlon interval can account for a number of basic free recall phenomena, however, has not been put forward. At the same time, empirical investigation has centered on rehearsal time (Rundus & Atkinson, 1970; Rundus, 1971) and has not examined item retention interval. Hence, previous experiments throw only a dim light on the explanatory power of rehearsal time combined with item retention interval. EXPERIMENT I
Serial position, presentation time, and delay of recall were varied in Experiment I. The question was, will the effects of these three variables on free recall be explainable through the mediation of rehearsal time and item retention interval ?
Method Subjects. Thirty-six introductory psychology students at the University of Western Ontario participated to fulfill a course requirement. Materials and apparatus. One-syllable nouns with a running frequency between 50 and 300 occurrences per million (both before and after the forms of each noun were combined using the procedure described by Thorndike and Lorge, 1944, p. ix) were selected randomly from Ku~era and Francis (1967). The nouns were assigned randomly to three practice lists and 12 experimental lists. Each list contained 18 nouns. The lists were presented on a memory drum at a rate of one noun every 1.25, 2.50, or 5.00 sec. The sound of the memory drum advancing and subjects' vocalizations were tape recorded. Procedure. Individual subjects were shown each list once, followed by a l-rain written free recall test. For each subject, the three practice lists were presented at different rates; on at least one practice list, recall was immediate; and on another practice list, recall was delayed for 15 sec. The experimental
lists were presented in six different random orders. Within each list order, presentation time and delay of recall were counterbalanced across trials within subjects, and across both trials and lists between subjects. At the start of the experiment, each subject was instructed that while the list was being presented, he should continually report which items he was thinking about. No restrictions were placed on the choice of list items to be rehearsed. At the start of each trial, subjects were told how fast the items would be presented. Following list presentation, subjects were asked to recall either immediately, or after counting backwards from a three digit number by threes for 15 sec.
Results As advocated by Myers (1972, pp. 176179), in all experiments, F ratios were evaluated using ultraconservative degrees of freedom for Fs which are clearly significant, and ultraliberal degrees of freedom for Fs which are clearly nonsignificant. Whenever these degrees of freedom failed to indicate unambiguously whether an F ratio was significant or not significant, the degrees of freedom were adjusted for the observed heterogeneity of variances and covariances. When the variances were heterogeneous, vertical bars in the graphs show + 1 standard error of each mean (vertical bars are omitted when the standard error lies inside the area encompassed by the plotted data point). When the variances were homogeneous, graphs show the average standard error of the mean. Recall. Recall data from experimental lists were analyzed by a 6 x 2 x 2 x 3 x 9 analysis of variance with list order (1 to 6) as a betweensubject factor, and delay (0 or 15 sec), trials (first or second), presentation time (1.25, 2.5, or 5 sec), and serial position (1 to 18 with two adjacent positions averaged) as within-subject factors. This analysis indicated that the main effects of delay, F(1, 30) --- 48.73, presentation time, F(1, 30) -- 58.52, and serial
FREE RECALL CURVES
551
position, F(1, 30)=43.92, were significant 2.37, p > .05, all other Fs(4, 120)~< 1.72, (p < .01). These main effects were qualified p > .05. Hence, in spite of subjects' overt by three significant interactions: between rehearsal, the present recall data conform to serial position and delay, F(1, 30)= 23.59, previous covert-rehearsal findings. p < . 0 1 ; serial position and presentation Rehearsal. Rehearsal time and item retentime, F(7, 205)=2.25, p < .05; and delay tion interval data were analyzed with the and presentation time, F(2, 47) = 4.63, same analysis of variance used to analyze p < .05. recall data. Like analysis of recall, analysis The effects of serial position, delay, and of rehearsal time data indicated that the presentation time on recall are shown in main effects of serial position, F(1, 30)--Figure 1. Inspection of this figure indicates 115.67, and presentation time, F(1,30)-that the interaction between serial position 226,909.39, were significant (p < .01) as well and delay resulted from poorer recall of as the interaction between serial position and terminal items and unchanged recall of presentation time, F(1, 30) = 75.54. All other preterminal items when recall was delayed for main effects and interactions were non15 sec. Figure 1 also suggests that the inter- significant (p > .05). Inspection of Figure 2 action between serial position and presentation indicates that the interaction between serial time resulted from longer presentation times position and presentation time resulted from increasing recall of items in preterminal longer presentation times producing larger positions more than items in terminal posi- increases in rehearsal time for the first items tions. Finally, Figure 1 suggests that the in a list than for later items. interaction between delay and presentation Like analyses of rehearsal time and recall, time was attributable to a delay producing analysis of item retention interval data larger reductions in recall when items were revealed that the main effects of serial position, presented either every 1.25 or 2.50 sec than F(1, 30)=226.19, and presentation time, when items were presented every 5 sec. F(1, 30) = 646.50, were significant (p < .01), as Since previous investigators (Murdock, well as the interaction between serial position 1962; Glanzer & Cunitz, 1966; Raymond, and presentation time, F(1, 30) = 37.33. More1969) have found that longer presentation over, delay had a significant effect on item times increase recall of all items, except the retention interval, F(1, 30) = 6,228.26, p < .01 immediate recall of terminal items, separate (as it had on recall but not on rehearsal time). analyses of variance were conducted across The main effect of delay, however, resulted beginning (1 to 6), middle (7 to 12), and merely from a delay increasing each item's terminal (13 to 18) items at each delay to retention interval by 15 sec. All other main determine whether similar results were ob- effects and interactions were not significant tained in the present experiment. These (p > .05). Figure 3 shows that item retention analyses and inspection of Figure 1 indicate intervals decreased across all positions except that longer presentation times increased the first, and that increases in presentation delayed recall of terminal items, and both time increased item retention intervals for immediate and delayed recall of beginning early items more than later items. and middle items, all Fs(1, 30)/> 11.20, The relation between recall, rehearsal time, p < .01. As expected, however, presentation and item retention interval is shown in Figure time did not alter immediate recall of terminal 4. Each point in Figure 4 represents mean items, F < 1. Moreover, these main effects recall and either mean rehearsal time (left were not qualified by any interactions between panel) or mean item retention interval serial position and presentation time; for im- (right panel) for a given presentation time, mediate recall of terminal items, F(3, 101) = delay, and pair of adjacent serial positions.
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Specifically, the left panel shows the relation between rehearsal time and recall, after recall has been adjusted by subtracting recall that can be predicted by item retention interval. On the other hand, the right panel shows the relation between item retention interval and recall, after recall has been adjusted by subtracting recall that can be predicted by rehearsal time. 10
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Individually, neither rehearsal time (r = .47, p < .01) nor item retention interval (r = -.37, p < .01) is highly correlated with recall. Rehearsal time and item retention interval together, however, do better: The multiple correlation coefficient is .86 (p < .01), where
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554
BRODIE AND PRYTULAK
mean recall = .25(log mean rehearsal time) .16(log mean item retention interval)+ .60. Plus and minus one standard error of the regression coefficients is _+.02 for both rehearsal time and item retention interval. As is to be expected, occasional marked deviations from the line of best fit occur. If there is any one condition for which deviations are consistently large, it is for the first pair of items in lists where items were presented every 1.25 sec. In each panel of Figure 4, data from this condition are represented by two triangles. One triangle in each panel represents immediate recall of the first two items in lists presented at a rate of one item every 1.25 sec, and the other triangle represents delayed recall of the same two items.
Discussion Experiment I replicates four phenomena already familiar to researchers in the area. First (Figure 4), recall is an increasing negatively accelerated function of rehearsal time, and a decreasing negatively accelerated function of item retention interval (Sanders, 1961; Hellyer, 1962; Pollatsek, 1969). Second (Figure 1), longer presentation times increase recall of all items except immediate free recall of terminal items (Murdock, 1962; Glanzer & Cunitz, 1966; Raymond, 1969). Third (Figure 1), small delays of recall decrease recall of items in terminal, but not preterminal positions (Postman & Phillips, 1965; Glanzer, Gianutsos, & Dubin, 1969). And fourth (Figure 2), at a long presentation time (5 see), rehearsal time is a decreasing negatively accelerated function of serial position (Rundus & Atkinson, 1970; Rundus, 1971), and as presentation time shortens to 2.50 and 1.25 see, rehearsal time approaches a ftat line. The central finding of Experiment I, however, is that the duration of rehearsal and time since last rehearsal can be viewed as the primary mechanism mediating the independent variables of serial position,
presentation time, and delay of recall, and the dependent variable of free recall. The most consistent deviation from this interpretation, moreover, was the incongruously good recall of the first two items in lists presented at the fastest rate. This incongrmty will be discussed further in Experiment IV. EXPERIMENT I I
One could explain the above results by assuming that while rehearsal is correlated with recall, it is not responsible for recall. That is, when items are presented slowly, subjects may choose to rehearse the items that they have already learned, so rehearsal follows learning and is neither learning itself, nor a contemporaneous manifestation of learning. Experiment II attempted to test this hypothesis by manipulating which items subjects rehearsed. If learning precedes rehearsal, or is independent of rehearsal, then changing the subject's rehearsal pattern should have little effect on recall curves and should impair rehearsal's ability to predict recall. If, on the other hand, altered rehearsal produces radical changes in recall even while rehearsal continues to predict recall then the tenability of the hypothesis that rehearsal plays a causal role in recall will be strengthened.
Metkod Subjects. Forty-eight introductory psychology students at the University of Western Ontario participated to fulfill a course requirement. None of these subjects had participated in Experiment I. Materials and apparatus. The materials and apparatus were the same as in Experiment I except that four practice and eight experimental lists were presented, and on every list a 6-mm line extended across the memory drum paper between the sixth and seventh items and between the twelfth and thirteenth items.
FREE RECALL CURVES
Procedure. Each subject was shown the 12 lists at the rate of one item every 5 sec. Before each list, the subject was told which of four rehearsal patterns to use; he used each pattern once on the four practice lists and twice on the eight experimental lists. The rehearsal patterns were as follows. In the Equal condition, subjects were told to think about each item only while it was being presented. In the remaining three conditions, subjects were told to think about the beginning items while the beginning items were being presented, but with different patterns being required for later items. In the Beginning condition, subjects were asked to spend half their time thinking about beginning, and half thinking about middle items, while middle items were being presented; and half their time thinking about beginning, and half about terminal items, while terminal items were being presented. In the Middle condition, subjects were told to think only about middle items while middle items were being presented, and to spend half their time thinking about middle items, and half about terminal items, while terminal items were being presented. Finally, in the Terminal condition, subjects were told to think about both beginning and middle items while middle items were being presented, but to think only about terminal items while terminal items were being presented. For each subject, the rehearsal instructions were counterbalanced across trials; and within groups of four subjects, the rehearsal instructions were counterbalanced across trials and lists. Each group of four subjects saw the experimental lists presented in a different random order. Each subject was instructed to continually report during list presentation which list items he was thinking about. Following presentation of each list, subjects were given a 1-min written free recall test on that list. For half the subjects, recall was immediate, whereas for the other half, recall was delayed for 15 sec of counting backwards by threes
555
from a three-digit number. After all lists had been presented, each subject was questioned to determine if he had violated the covert rehearsal instructions.
Results Recall. The recall data were analyzed with a 6 x 2 x 2 x 4 x 9 analysis of variance with list order (1 to 6) and delay (0 to 15 sec) as between-subject factors; and trials (first or second), rehearsal pattern (Equal, Beginning, Middle, or Terminal), and serial position (1 to 18 with two adjacent positions averaged) as within-subject factors. This analysis revealed that the main effects of delay, F(1, 36) = 9.91, rehearsal pattern, F(1, 36) = 13.54, and serial position, F(1, 36)= 67.63, were significant (p < .01). These main effects were qualified by two significant (p < .01) interactions: between serial position and delay, F(1, 36) = 19.48, and between serial position and rehearsal pattern, F(1, 36)= 23.50. All other main effects and interactions were nonsignificant (p > .05). Like recall data in Figure 1, recall data in Figure 5 indicate that the interaction between serial position and delay resulted from poorer recall of terminal items and unchanged recall of preterminal items when recall was delayed for 15 sec. Figure 5 also indicates that within the portion of the list after which the rehearsal pattern was named, recall was raised unevenly, with the first items in the portion receiving the largest increase in recall. As a result, compared to the slope in the Equal condition, the slope across beginning items in the Beginning condition became more negative, the slope across middle items in the Middle condition changed from zero to negative, and the slope across terminal items in the Terminal condition changed from positive to close to zero in the I condition and negative in the D condition. More briefly, these changes in recall can be summarized as the exaggeration, or the production, of local primacy effects in the list portion selected for increased rehearsal.
556
BRODIE AND PRYTULAK EQUAL
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FIO. 5. Proportion of items recalled in Experiment II as a function of serial position and rehearsal pattern (Equal, Beginning, Middle, or Terminal) when recall was either immediate (I) or delayed (D). The confidence interval on the upper right encloses+ 1 standard error of each mean. Rehearsal. Rehearsal time and item retention interval data were analyzed with the same analysis of variance used to analyze recall data. Like analysis of recall data, analysis of rehearsal time data indicated that the main effect of serial position, F(1, 36)= 522.93, and the interaction between serial position and rehearsal pattern, F(1, 36)=226.48, were significant (p < .01). All other main effects and interactions were not significant (p > .05). Inspection of Figure 6 indicates that the interaction between serial position and rehearsal pattern resulted from all rehearsal patterns except Equal producing a sharp negative slope in rehearsal time across beginning positions, and from Middle and Terminal rehearsal patterns producing a sharp negative slope in rehearsal time across middle and terminal positions, respectively. Like analyses of rehearsal time and recall data, analysis of item retention interval data
indicated that the main effect of serial position, F(1, 36)= 1,566.65, and the interaction between serial position and rehearsal pattern, F(1, 36)= 172.95, were significant (p <.01). Moreover, like recall, but unlike rehearsal time, the main effects of rehearsal pattern, F(1, 36)=698.09, and delay, /7(1, 36)= 1,162.22, were significant (p<.01). The main effect of delay resulted from a delay increasing each item's item retention interval by 15 sec. All other main effects and interactions were not significant (p > .05). As can be seen in Figure 7, the interaction between serial position and rehearsal pattern resulted from the rehearsal patterns shortening the item retention intervals in the list fractions after which the rehearsal patterns were named, and rotating the slopes counterclockwise so as to make them positive (across beginning items in Beginning and Terminal conditions and across middle items in the
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Middle condition), zero (across beginning items in the Middle condition), or less strongly negative (across terminal items in the Terminal condition). The relation between recall, rehearsal time, and item retention interval is illustrated in Figure 8. Each point in Figure 8 represents mean recall and either mean rehearsal time
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FIG. 7. Mean item retention interval in seconds (Expernnent II) as a function of serial position and rehearsal pattern (Equal, Middle, Terminal, or Beginning). To avoid crowding, the line representing the Terminal rehearsal pattern is displaced slightly to the right, and the line representing the Beginning rehearsal pattern to the left. Confidence intervals enclose + 1 standard error of each mean.
(left panel) or mean item retention interval (right panel) for a given rehearsal pattern, delay, and pair of adjacent serial positions. Specifically, as in Figure 4, the left panel in Figure 8 shows the relation between rehearsal time and recall, after recall has been adjusted
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558
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by subtracting recall that can be predicted by continue to be highly correlated when item retention interval; and the right panel subjects are required to alter their usual shows the relation between item retention rehearsal pattern. Moreover, inspection of interval and recall, after recall has been Figures 4 and 8, as well as comparison of the adjusted by subtracting recall that can be regression coefficients obtained in Experipredicted by rehearsal time. ments I and II, indicate that manipulating a Individually, neither rehearsal time (r =.64, subject's rehearsal has little or no effect on p < .01) nor item retention interval (r = -.47, the slope of the rehearsal time and item p < . 0 1 ) is highly correlated with recall. retention interval regression curves. These Rehearsal time and item retention interval findings encourage the supposition that together, however, do better: The multiple changes in rehearsal are responsible for correlation coefficient is .89 (p < .01), where changes in recall, not only when subjects mean recall = .28(Iog mean rehearsal time) are free to rehearse whichever items they .15(log mean item retention interval)+ .50. choose, but also when they are required to Plus and minus one standard error of the follow a prespecified pattern of rehearsal. regression coefficients is _+.02 for rehearsal As in Experiment I, most of the effects of time and _+.01 for item retention interval. serial position on recall in the present experiif, as in Experiment I, we search for the ment can be predicted from changes in conditions with consistently large deviations rehearsal time and item retention interval. from the line of best fit, we find that they are Nevertheless, one finding is particularly immediate and delayed recall of the first troublesome--namely, a primacy effect in pair of items in the Equal condition (repre- the Equal condition where subjects were sented by triangles in Figure 8) and in the instructed to rehearse each item only while it Terminal condition (represented by squares). was being presented (see Figure 5). Other Perhaps rehearsal time and item retention investigators have also obtained primacy interval data failed to predict some changes effects using similar instructions (Glanzer & in recall because subjects covertly disobeyed Meinzer, 1967; Leicht, 1968; Fischler, Runthe rehearsal instructions. Despite almost dus, & Atkinson, 1970). If subjects do obey perfect compliance with instructions to limit their rehearsal instructions, then these findovert rehearsals to specific items, at the end ings would suggest that duration of rehearsal of the experiment most subjects reported and time since last rehearsal are not the sole that they had violated instructions to limit determinants of the primacy effect. In fact, their covert rehearsals to specific items. however, subjects admit disobeying rehearsal That is, 36 of the 48 subjects tested reported instructions when rehearsal is covert (Welch that: (a) in the equal condition, they covertly & Burnett, 1924; Leicht, 1968). Until now, rehearsed beginning items while later items however, overt rehearsal has been accepted were being presented; (b) In the middle as an accurate reflection of covert rehearsal, condition, they covertly rehearsed beginning and the possibility that subjects overtly items while either middle or terminal items obey rehearsal instructions while covertly were being presented; and (c) In the terminal disobeying them has not been investigated. condition, they covertly rehearsed beginning The discrepancy between overt and covert or middle items while terminal items were rehearsal is examined in Experiments III and being presented. IV. Discussion
The results from the present experiment clearly indicate that rehearsal and recall
EXPERIMENTIII Perhaps subjects in Experiment II disobeyed instructions to covertly rehearse each
FREE RECALL CURVES
559
item only while it was being presented because when learning other lists, they were required to overtly rehearse the first items while later items were being presented. Alternatwely, perhaps subjects became confused at the end of the experiment and incorrectly reported that they had covertly rehearsed earlier items while later items were being presented. Experiment III was conducted to get subjects to obey equal rehearsal instructions, and to obtain more accurate and precise information on which items subjects covertly rehearse when learning under equal rehearsal instructions. This was attempted by having subjects participate in only one condition, and by having subjects indicate, after concurrent overt rehearsal, which items they had usually rehearsed aloud, as well as which items they had rehearsed covertly during list presentation. If subjects can accurately report which items they rehearsed aloud, then we can be more confident that they will also be able to accurately report which items they rehearsed covertly. Moreover, if the measure of covert rehearsal time for the first items in a list is longer, or covert item retention interval is shorter, than suggested by overt rehearsal (whether measured by concurrent vocalization or later reproduction) then we will have reason to suppose that rehearsal is responsible for the primacy effect even when subjects are required to restrict their overt rehearsal to the item being presented.
Each subject was instructed to continuously articulate the list words that he was thinking about while the list was being presented, to think about each item only while it was being presented, and to obey the rehearsal instructions, even if obeying the instructions reduced the number of items he could learn and recall. Immediately following list presentation, subjects were given a l-rain written free recall test on that list. Following recall of the sixth list, subjects were given a rehearsal reproduction sheet. Half the subjects were instructed first to use numbers to indicate as closely as possible which word or words they usually said aloud while each word was being presented during the last four lists. As examples on how to fill out this sheet, each subject was told to put a 1 next to word 1 if he had usually said the first word while it was being presented, and to put either 2, 1, or 1 and 2 next to word 2 depending on whether he had usually said only word 2, only word 1, or both words 1 and 2 while the second word was being presented. After each subject had indicated which words he had usually said, he was handed another rehearsal reproduction sheet, and the earlier instructions were repeated with the words "thought about" inserted for the words "said aloud." The other half of the subjects first indicated which words they usually thought about, then which words they usually said aloud.
Method Subjects. The subjects were 24 University of Western Ontario introductory psychology students who had not participated in either Experiment I or II.
Results
Materials and apparatus. The materials and apparatus were the same as those used in Experiment I, except for the addition of rehearsal reproduction sheets with "word 1" to "word 18" printed in a vertical column. Procedure. Individual subjects were shown two practice and four experimental lists presented at a rate of one item every 5 see.
Recall. Recall data were analyzed by a 4 x 9 analysis of variance with trials (1 to 4) and serial position (1 to 18 with two adjacent positions averaged) as within-subject factors. Only the main effect of serial position, F(1, 23)=26.29, was significant (p <.01). The effect of serial position on recall was essentially the same as that shown in Figure 5 for immediate recall in the Equal condition. That is, the probability of recall in the present experiment decreased from .57 to .36 across beginning positions, remained fairly constant
560
BRODIE AND PRYTULAK
at .34 across middle positions, and increased to .91 across terminal positions. Rehearsal All subjects vocalized each item only while it was being presented, and after all lists had been presented they correctly reported that they had vocalized each item only while it was being presented. However, even though each subject was instructed to also covertly rehearse each item only while it was being presented, all subjects reported disobeying the covert rehearsal instructions. Specifically, each subject reported from 3 to 44 covert violations per list (that is, covertly rehearsing earlier items while later items were being presented). Moreover, half the subjects reported over 11 violations per list, and the mean number of violations per subject per list was 14.8 with a standard deviation of 11. Rehearsal time and item retention interval data from subjects' reproductions of their covert rehearsal were analyzed with serial position (1 to 18 with two adjacent positions averaged) as the only within-subject factor. These analyses revealed significant (p < .01) effects of serial position on both rehearsal time, F(1, 23)--15.01, and item retention interval, F(1, 23)= 123.25. Serial position decreased rehearsal time from 7.36 sec for the first items to between 4 and 5 sec for later items. Similarly, serial position decreased item retention intervals from 63.25 sec for the first items to 1.96 sec for the last items. Rehearsal time and item retention interval data from subjects' concurrent overt rehearsals and from subjects' reproductions of their overt rehearsals could not be analyzed because neither measure varied between subjects. That is, rehearsal time for each item in the list was always 5 sec, and item retention intervals always decreased linearly from 82.50 for the first items to 2.50 sec for the last items.
Discussion As in Experiment II, the present results indicate that requiring subjects to continu-
ously vocalize only the item being presented does not ensure that they will obey instructions to avoid covertly rehearsing earlier items. Moreover, unlike Experiment II, the present results show that subjects' overt rehearsal selectively underestimates rehearsal time and overestimates item retention interval for beginning items. As a result, overt rehearsal predicts lower recall for beginning items than is in fact observed. Recomputing rehearsal time and item retention interval for the first two items in the Equal condition in Experiment II (by adding the difference between reproduction-covert and either reproduction-overt or concurrent-overt to rehearsal time and item retention interval) has the effect of reducing the discrepancy between predicted and observed recall by about two-thirds. Hence, the present results provide additional evidence that serial position alters recall through the mediation of rehearsal, even when subjects are instructed to rehearse each item only while it is being presented. EXPERIMENTIV Perhaps like the discrepancy between rehearsal and recall in the Equal condition in Experiment II, the discrepancy observed in Experiment I when items were presented quickly resulted from subjects selectively failing to report all rehearsals of the first words in a list. As in Experiment III, this possibility was tested in the present experiment by having subjects indicate, after concurrent overt rehearsal, which items they had rehearsed aloud, as well as which items they had rehearsed covertly during list presentation.
Method The subjects were 24 University of Western Ontario introductory psychology students who had not participated in any of the previous experiments. The materials, apparatus, and procedure were the same as those used in Experiment II, except lists were presented at a
561
FREE RECALL CURVES
rate of one item every 1.25 sec and no restrictions were placed on the choice of list items to be rehearsed. Results Recall. Analyzing recall with the analysis of variance specified in Experiment III indicated that only the main effect of serial position, F(1, 23)=55.52, was significant (p < .01). The effect of serial position on recall was essentially the same as that shown in Figure 1 for immediate recall when items were presented for 1.25 sec. That is, the probability of recall in the present experiment decreased from .56 to .18 across beginning positions, remained fairly constant at .22 across middle positions, and increased to .90 across terminal positions. Rehearsal. The concurrent-overt rehearsal and rehearsal reproduction data were analyzed by 3 x 9 analyses of variance with report of rehearsal (concurrent-overt, reproductionovert, or reproduction-covert) and serial position (1 to 18 with two adjacent positions averaged) as within-subject factors. Analyses of rehearsal time and item retention interval data indicated that the main effects of serial position, both Fs(1, 23)/> 10.29, p < .01, and report of rehearsal, both Fs(1, 28)/> 6.99, p < .05, were significant. On the other hand, neither interaction between serial position and report of rehearsal was significant, both Fs(2, 34) ~<2.51, p > .05. Since it was expected that differences in rehearsal time and item retention interval as a function of different methods of reporting rehearsal would be limited to the first serial positions, separate analyses of variance were conducted across beginning, middle, and terminal positions. As expected, these analyses indicated that the main effect of report of rehearsal was significant for rehearsal time, F(2, 38)= 6.46, p < .01, and item retention interval, F(1, 31)=6.14, p < . 0 5 , across beginning positions, but not across middle or terminal positions, all Fs(2, 46)42.14, p > .05. The main effects of report of rehearsal
across beginning positions were due to concurrent-overt and reproduction-overt measures yielding lower estimates of rehearsal time (1.72 and 1.83 sec) and higher estimates of item retention interval (18.06 and 18.18 sec) for the first two items in a list than those obtained with a reproduction-covert measure (rehearsal time, 2.21 sec; item retention interval, 15.95 sec). Discussion
Like Experiment III, the present results suggest that estimating overt rehearsal time and item retention interval from subjects" reproduction of their overt rehearsals gives results almost identical to those obtained from subjects' concurrent overt rehearsal. Subjects' ability to reproduce their overt rehearsals encourages the belief that they could also accurately reproduce their covert rehearsals. Comparisons of the reproduction-covert data with both the concurrent-overt and reproduction-overt data indicates that the latter measures underestimate rehearsal time and overestimate item retention intervals for the first two items. Increasing rehearsal time and reducing item retention intervals by the difference between reproductioncovert and concurrent-overt conditions would reduce by about one-third the discrepancy between predicted and observed recall of the first two items in lists presented quickly in Experiment I. Hence, although these points would still deviate from the regression curves, their deviation would be less striking. Consequently, the present results lend further support to the hypothesis that rehearsal does in fact produce the primacy effect even when items are presented quickly. GENERAL DISCUSSION
The results from the present series of experiments support the hypothesis that serial position, delay, and presentation time alter free recall by first altering rehearsal time and item retention interval. That is,
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BRODIE AND PRYTULAK
immediate free recall is a U-shaped function of serial position (Figure 1) because subjects rehearse beginning items more (Figure 2) and terminal items later (Figure 3) than middle items. The increases in item retention intervals, produced by increasing delay of recall, lower recall of terminal items only (Figure 1) because extending item retention intervals has more effect (Figures 4 and 8) on items with short item retention intervals (terminal items, Figure 3) than on items with alreadylong item retention intervals (beginning and middle items, Figure 3). Finally, longer presentation times increase immediate free recall of beginning and middle items only (Figure 1) because of an increased rehearsal time (Figure 2) which is not offset by a concomitant increase in an already-long item retention interval (Figures 3 and 4). Like beginning and middle items, immediate free recall of terminal items varies with changes in rehearsal (Figure 5). Increased rehearsal time at longer presentation times (Figure 2), however, does not increase immediate free recall of terminal items (Figure 1) because it is neutralized by the potent increase in short item retention intervals (Figure 3). The finding that rehearsal can account for the effects of serial position, delay of recall, and presentation time on free recall encourages the supposition that rehearsal can also account for the effects of several other manipulations. This supposition is supported by previous research (Rundus, 1971) that indicates that when no restrictions are placed on rehearsal, rehearsal accurately predicts spacing and isolation effects in free recall. Whether spacing and isolation effects can be eliminated by having subjects rehearse each item only while it is being presented is not known. The present results, however, suggest that subjects will disobey equal-rehearsal instructions. Hence, any tests of the relation between rehearsal and recall must rely on more than the investigator's instructions and the subjects' concurrent overt rehearsals.
Instead, as demonstrated by Reitman's (1971, 1974) reversed conclusion concerning the presence of rehearsal during a signal-detection task, before dismissing rehearsal as an explanation it is necessary to verify the accuracy of the measure of rehearsal being used.
REFERENCES FISCHLER, I., RUNDUS,D , & ATKINSON,R. C. Effects
of overt rehearsal procedures on free recall. Psychonomic Science, 1970, 19, 249-250.
GLANZER,M. Storage mechanisms in recall. In G. H. Bower (Ed.), The psychology of learning and mottvation: Advances m research and theory.
New York: Academic Press, 1972. Vol. 5. Pp. 129-193. GLANZER, IV[., & CUNITZ, .A.R. Two storage mechanisms in free recall. Journal of Verbal Learning and
Verbal Behavior, 1966, 5, 351-360. GLANZER, M, GIANtrTSOS, R., & DUBIN, S. The removal of items from short-term storage. Journal of Verbal Learning and Verbal Behavior,
1969, 8, 435-447. GLANZER,M., & MEINZER,A. The effects of lntralist activity on free recall. Journal of Verbal Learning and Verbal Behavior, 1967, 6, 928-935 GRUNEBERG,M. M. A dichotomous theory of memory unproved and unprovable? Acta Psyehologiea, 1970, 34, 489-496. HELLYER,S Frequency of stimulus presentation and short-term decrement in recall. Journal of ExperimentalPsyehology, 1962, 64, 650 KU6ERA, H., & FRANCIS, W. N. Computational analysis of present-day American English. Providence, RI' Brown Umverslty Press, 1967 LEICnT, K. L. Dafferential rehearsal and primacy effects Journal of Verbal Learning and Verbal Behavior, 1968, 7, 1115-1117. MURDOCK,B. B., JR. The serial position effect in free recall. Journal of Experimental Psychology, 1962, 64, 482-488 MYERS, J. L. Fundamentals of experimental design. Boston' Allyn and Bacon, 1972. 2nd ed. POLLATSEK,A. Rehearsal, interference, and spacing of practice in short-term memory Technical Report, Human Performance Center, University of Michigan, 1969. C~tedby Bjork, R. A., Repetition and rehearsal mechanisms in models for short-term memory. In D. A. Norman (Ed.), Models of human memory. New York" Academic Press, 1970. P. 325.
FREE RECALL CURVES
POSTMAN,L., & PHILLIPS,L. W. Short-term temporal changes in free recall. Quarterly Journal of ExperimentalPsychology, 1965, 17, 132-138. RAYMOND, B. Short-term storage and long-term storage in free recall. Journal of VerbalLearning and VerbalBehavior, 1969, 8, 567-574. ROBINSON, E. S., t~ BROWN, M. A. Effect of serial position upon memorization. American Journal of Psychology, 1926, 37, 538-552. REITMAN, J. S. Mechanisms of forgetting in shortterm memory. Cognitive Psychology, 1971, 2, 185-195. REITMAN, J. S. Without surreptitious rehearsal, information in short-term memory decays.
Journal of Verbal Learning and Verbal Behavior, 1974, 13, 365-377. Ru~,aJus, D. Analysis of rehearsal processes in free recall. Journal of Experimental Psychology, 1971, 89, 63-77.
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RLrNDtrS, D. Output order and rehearsal in multi-trial free recall. Journal of VerbalLearning and Verbal Behavior, 1974, 13, 656-663. RUNDUS,D., & ATKINSON,R. C. Rehearsal processes in free recall: A procedure for direct observation.
Journal of Verbal Learning and Verbal Behavior, 1970, 9, 99-105. SAr,rDERS, A. F. Rehearsal and recall in immediate memory. Ergonomtcs, 1961, 4, 29-34. THORNDIKE, E. L., & LORGE, I. The teacher's word book of 30,000 words. New York: Columbia University Press, 1944. WELCH,G. B., & BURNETT,C. T. Is primacy a factor in association-formation? American Journal of Psychology, 1924, 35, 396-401.
(Received May 19, 1975)