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Repeated recall in short-term memory
JOURNAL
OF VERBAL
LEARNING
AND VERBAL
Repeated
7, 358-365 (1968)
BEHAVIOR
Recall
in Short-Term
Memory’
D. J. MURRAY Queen’s
University,
Kingston,
Ontario,
Canada
Lists of eight letters were either voiced or silently read at presentation, ihe presentation rate being either 1,2, or 3 letters/set. Immediate spoken recall was then given, three times in succession. It was found that accuracy of recall decreased over successive recalls, with errors in the early recalls tending to be perpetuated over later recalls; that the rate of recall was faster for rapidly presented lists than for slowly presented lists, but also increased over successive recalls; and that the loudness of recall decreased over successive recalls. The relationships between successive recalling, postlist rehearsal, and learning are discussed with reference to these results,
When a list is memorized
for immediate recall, rehearsal can take place either during the presentation of the list, provided the presenta-
tion rate is fairly slow (Posner, 1963), or in the interval between presentation and recall (Sanders, 1961). With respect to the former, it has been shown that when intralist rehearsal is prevented by having irrelevant items interspersed among the items to be memorized, recall is reduced (Murray, 1966a); and with respect to the latter, it is known that if postlist rehearsal is prevented by asking Ss to perform a task during the interval, the reduction in recall is a direct function of the duration of the interfering activity (Peterson and Peterson, 1959). But despite the consensus that rehearsal is important, if not indeed necessary, for the retention of verbal items, there is little evidence as to what Ss actually do during rehearsal. The purpose of the present study was to obtain evidence which would at least be suggestive of events occurring during postlist rehearsal. In particular, we desired to know the extent to which errors might be perpetuated across successive recalls. If this result were obtained, it * This research was supported by N.R.C. Grant APB-126. I am extremely grateful to E. Griffiths for constructing the transducer used with the polygraph, to L. Burgoyne for assistance particularly in the collection of the data, and to H. Seth for research assistance throughout.
would suggest that successive retrievals were based on “memories” of the preceding recalls rather than upon some basic trace structure laid down at presentation. It is, of course, difficult to specify, in other than an introspective manner, how retrieval might proceed in subvocal rehearsal. But it seems reasonable to assume that, if persons are asked to recall a list several times in succession, any patterns which emerge over the course of successive vocalized recalls are likely also to be found in the case of successive subvocal rehearsal acts. This assumption has to some extent been justified by the results of a preliminary study (Murray, 1967), in which it was shown that, provided immediate recall was forced-order, no important differences in serial-position effects resulted from recall after two voiced rehearsals as opposed to two silent rehearsals. (Recall after voiced rehearsal was, however, lower than recall after silent rehearsal). In the following experiment, therefore, Ss were asked to recall immediately, aloud, several times, material which had been presented once under one of various presentation conditions. The choice of presentation conditions was determined by considerations arising from previous work. One obvious variable worthy of examination was that of presentation rate. A number of authors (see Posner’s review, 358
REPEATED RECALL IN STM
1963; and Postman, 1964) have stressed that slow presentation permits of more intralist rehearsal than does fast. However, the efficiency of recall is also a function of the nature of the responses given by S at presentation : if lists were vocalized by Ss, the advantage for recall of vocalization as opposed to silent reading was enhanced at the faster rates (Murray, 1966b). The present study therefore investigated both presentation rate and vocalization at presentation. Recall rates were also examined, partly because it had incidentally been found in earlier work that recall rates tended to parallel presentation rates (Murray, 1964, p. 147), and partly because it was felt that the process of rehearsal might involve increased “chunking,” which would be reflected in increasing recall rates across successive rehearsals. To obtain recall times in the present study, a polygraph was used: this had the advantage of also allowing recall loudness to be recorded, though no specific predictions were made as to the outcome of an analysis of this characteristic of spoken recall. It might be noted that other authors have found that successive recalls of paired associates, without feedback as to the correctness of the various recalls, have tended to increase in accuracy rather than decrease (Richardson and Gropper, 1964). Experiments using the Estes RTT paradigm have however found little evidence of shifts from incorrect to correct across successive recall trials (e.g., Jones, 1962). The present study was expected to reveal what might happen in the case of the immediate repeated recall of a list of eight letters presented just once.
359
of paper which could be fed through an arrangement of rollers above which was a viewing-slit permitting only one letter to be exposed at a time. By appropriate spacing of the items on the roll, the single letters could appear at rates of 1,2, or 3 per sec. On each roll there were 16 lists, all at the same presentation rate: a total of nine rolls was drawn up, with each of the three presentation rates being allotted three blocks of lists (see “Design”). Design. Each S worked through three rolls, one at each presentation rate. On each roll half the lists were voiced and half silently read. The orders in which Ss worked through their six conditions were counterbalanced across the experiment, apart from the restriction that the two vocalization conditions on any rate were carried out consecutively by each S. To avoid any artifacts of list difficulty, three different blocks of 16 lists were used, these blocks also being counterbalanced across conditions. Procedure. On arrival Ss were shown written instructions outlining their task, and six practice lists, one under each vocalization/presentation rate condition, werecarried out. The Sthen worked through his three rolls (48 lists). Forpresentation, Ss were instructed either to read the lists silently (without mouth movements), or voice each letter aloud as it appeared. The machine was switched off as E saw the last letter of a list pass the viewing slit. For recall, S started to recall “assoonasheliked’afterthemachinewasswitchedoff. He spoke three successive recalls into a tape recorder: the recalls were also written down by E as a further check. The S was told always to start each recall with the first presented letter and continue through to the end in order, leaving no omissions (forced-order recall). Each S’s single session lasted about 45 min. Analysis of .results. The tape recordings obtained from each S were played via a specially constructed transducer into the input of a Grass polygraph (Model SDWCl), with the sensitivity set at a constant value of 8. As each letter was sounded from the tape, this resulted in a deflection of the pen recorder on the polygraph (paper speed, 25 mm/set). This record could be used to determine (a) the timing between recalled letters and between lists, obtained by checking each deflection against a time base, and (b) the relative loudness of the spoken letters, given by the amplitude METHOD of the deflection representing each letter. To obtain General. The Ss were visually presented with lists of suitable readings, the playback intensity of the tape eight consonants for immediate recall. The letters were recorder was set for each Sso that the averagedeflection either silently read (R) or voiced (V) at presentation, of the polygraph pen was, so far as could be judged and were shown at rates of 1,2, or 3 letters/set. Recall visually, about the same for each S. Thus, despite was spoken immediately after the last letter, and three variations in the normal loudness of S’s voices as successive recalls were given (these will be denoted as compared with each other, the records were reasonably recalls I, II, III respectively). comparable between Ss, and certainly comparable Material. Lists of eight consonants, drawn from the within Ss. On all voiced trials, both S’s reading aloud pool described by Murray (1965), were typed onto rolls at presentation and his recalls were recorded on the
360
MURRAY
polygraph: on silently read trials, there was obviously no sound during presentation, but the switch-off of the memory drum made a clear signal which could be used for determining the latency between the end of presentation and the start of the first recall. Each recording was first gone through to delete any deflections due to background noises, etc. Then scores were taken of the total time required for each recalled list (from which mean time per letter could be derived), and the intervals between successive recalls. In all cases the time intervals were measured between peaks of deflections. The latency of the first recall was judged by the interval between the click caused by the switch-off of the memory drum and the start of the first recall. Finally an index of loudness was obtained for each recalled list: the index was the number of deflections per list (maximum possible, 8) which crossed the time base on the polygraph record. The more loudly a list was recalled, the more such crossings there were. More elaborate (and laborious) measures of loudness could of course be made, but we found that the results of this simple procedure were clear enough for definite conclusions to be drawn about variations in the loudness of spoken recall across successive recalls. Subjects. The Ss were 18 psychology students (mainly graduate) from Queen’s University, all of whom had had experience with memorizing using letter lists and the present apparatus (in experiments held about a year previously). They were aware that their recall was being tape recorded, but were not told
that the timing and loudness of recall were going to be examined. RESULTS
The results with respect to number
correct, timing of recalls, and loudness of recalls, will be reported separately, and then an overall picture will be given.
Number Correct. Figure 1 shows the per-
centages of letters correct (in their correct position in the list) as a function of presentation rate, voicing condition, and recall numbers (I, II, III). Analysis of variance applied to the raw data showed that there was a significant decrease
in the number
correct
across re-
calls, F(2, 68) = 70.51, p < .OOl, and a significant variation among Ss, F(17, 34) = 11.43, p < .OOl. Although when tested against the remainder, the effects of both vocalization and of presentation rate were highly significant (p < .OOl), when tested against the significant Vocalization x Rate mean square, F(2, 34) = 4.05,~ < .04, neither was significant. The interaction is shown in Fig. 1: vocalized lists were best recalled at the medium rate, and silently
?O-
I
lx
m
RECALL
FIG. 1. Percentage correct as a function ---- v;---R.
of vocalization
condition,
presentation
rate, and recall number;
REPEATED
RECALL
read lists at the slowest rate. This interaction has also been found in previous work (Murray, 1966b); in the present study, however, the Vocalization x Rate x Ss interaction was also significant, F(34, 68) = 8.49, p -c .OOl. The finding we wish to emphasize here, however, is
that as recall was repeated, there were increasing errors over successive recalls, with the rate of this increase being independent both of vocalization at presentation and of presentation rate.2 The recall data were then examined in detail to determine the nature of this increasing error TABLE PROPORTIONS
OF EACH KIND
IN
361
STM
the corresponding serial position of Recall II and that item in turn with its counterpart in
Recall III. With “CCC” used to denote that a given letter was correct across all three recalls, “NNN” to denote that it was incorrect across all three recalls, “CCN” to denote that it was correct in Recalls I and II but not in III, and so on, the percentage occurrences of all eight possible combinations were worked out (Table 1). Apart from a higher frequency of NNN cases following silent reading as opposed to voicing -as would be expected, given the data shown in Fig. l-there were no apparent differences 1
OF ERROR SHIFT OVER THE THREE RECALLS CONDITIONS
UNDER THE
SIXPRESENTATION
Presentationconditions Vocalization rate
V 1
ccc
.350
CCN
.051
CNC
.008 .075 .015 .017 .016 .469
CNN NCC NCN NNC NNN
R
2
3
1
2
3
Mean
.418 a43 .017 .082 .017 .012 .021 .391
.334 .051 .015 .120 .022 .016 .012 .431
,333 .027 1.00 .049 .OlO .009 .007 .553
.303 a45 .008 .060 ,012 .007 .012 .553
.271 .029 .009 .048 .016 .005 .012 .610
.305
rate across recalls. Each separate letter in
Recall I was compared with its counterpart in ZIt might be asked whether the decreasein performance over successiverecalls was related to any proactive inhibition effects accumulating over the session.If the sessionswere divided into thirds (16 lists each), the decreaseover successiverecallsshowed up clearly for each third of the session. Moreover, performance improved, rather than decreased,over the whole session.Given that the conditions were counterbalanced over session-thirds,it thus seems doubtful that the validity of the above resultswould be affectedby PI artifacts. It wasnoted, however,that for the veryfirst list, 12out of the 18Ss did equally well on all three recalls.It may have been that PI effectswere operative over the first few listsof the sessiononly.
.041 .012 .072 .015 .OOl .013 .501
of importance between Rand V with respect to the different types of combination. Essentially, Table 1 shows that an item correct on recall I had a high probability of being correct on Recall II and III, while items incorrect
on
Recall I were likely to stay incorrect on Recalls II and III. The overall downtrend in number correct across successive recalls is reflected in
the incidence of CCC, CNN, and CCN cases, respectively. This analysis does not tell us, however, whether an error in Recall I will be perpetuated throughout Recalls II and III, or whether the error will change (i.e., if “B” is wrongly
362
MURRAY
TABLE
2
ANALYSIS OF NNN (PROPORTIONS
OF ERROR
PRESERVATIONS
CASES AND ERROR
Between recalls I and II Proportions of errors which were:
Changed
Preserved
Changed
V
1 2 3
.657 .626 .568
.343 .374 .432
.712 .728 .731
.288 .272 .269
R
1 2 3
.719 .686 .707
.281 .314 .293
.813 .777 .748
.187 .223 .252
times per recall and on the interrecall intervals (the latter including the interval between machine switch-off and the start of the first recall). On times per recall, there was a significant Vocalization x Rate x 5’s interaction, F(34, 68) = 4.01, p < .Ol. Significant two-way interactions were found for Recall Numbers x Ss, F(34,68) = 1.83, p < .05, and for Vocalization x Recall Number, F(2, 68) = 6.46, p -C.Ol. In the latter case, while later recalls were consistently shorter than were earlier recalls, the
TABLE RECALL
TIMES
Between recalls II and III
Preserved
recalled as 7” on Recall I, will it also be recalled as “V” on Recall II, or as some other letter?). Table 2 shows an analysis of NNN cases for each of the six main conditions: it can be seen that, for all conditions, the probability of an error’s being perpetuated across all three recalls was at least double that of its being changed from recall to recall. Timing of Recall. Table 3 shows the mean times per recall and mean interrecall intervals obtained under the main conditions. Separate analyses of variance were carried out on the
MEAN
CHANGES)
AND INTERRECALL
INTERVALS
3
FOR RECALLS CONDITIONS
Recall times (set) Presentation rate (item/@
I, II,
AND
Interrecall
III
UNDER
THE SIX PRESENTATION
intervals (xc)
I
II
III
I
I-II
II-III
R
1 2 3
5.88 5.32 4.57
4.32 3.94 3.99
4.25 3.79 3.69
2.06 2.05 1.75
1.59 1.55 1.38
1.38 1.41 1.19
V
1 2 3
5.25 4.25 4.03
4.49 4.06 3.74
4.20 3.66 3.56
1.91 1.34 1.31
1.38 1.25 1.31
1.57 1.46 1.45
4.88
4.09
3.86
1.74
1.41
1.41
Mean
REPEATED
RECALL
IN STM
363
difference was most marked for silently read ness of each recall decreased, the effect being lists as opposed to voiced lists. As a conse- more marked for R than for V lists, and for quence of this interaction, the main effects of slow than for medium or fast lists. Interrelationships Between Number Correct, neither vocalization nor of recall were signifiRecall-Time, and Recall-Loudness. Although cant, but it is clear from Table 3 that time per the above results appear complicated, there recall decreased across successive recalls. The are a number of common threads that can be effect of presentation rate upon recall rate was significant, however, F(2, 34) = 8.50, p < .Ol : teased out from the mass. First, in all measures, the faster the presentation rate, the more rapid save that of time per recall, there was a signifithe first, and subsequent, recalls. This is the cant three-way interaction of Vocalization, Rate, and Ss. This can be taken to indicate that most obvious feature shown in Table 3. The analysis of interrecall intervals showed there are large individual differences in the a large number of interactions significant at degree to which persons found vocalization at the .05 level and less: Vocalization x Recall presentation affecting their recall following any Number, F(2, 68) = 15.99; Vocalization x particular presentation rate. Second, on all Rate, F(2, 68) = 3.66; Vocalization x Ss, analyses save that of number correct, Recall F(17, 68) = 2.02; Recall Number x Ss, F(34, Number x Ss interactions were significant; 68) = 2.92; and Rate x Ss, F(34, 68) = 2.10. thus there was a high degree of concordance When the main effects were tested against among Ss with respect to the decrease in these interactions, only the Ss factor yielded a number correct over successive recalls, but significant variance ratio, F( 17, 34) = 22.9, less concordance with respect to other trends over successive recalls. And third, for all p < .Ol. Many of these interactions merely reflected subject variability. The most imporanalyses except that of numbers correct, trends tant results seemed to be that (a) interrecall over successive recalls were more marked intervals decreased over successive recalls, the following silent reading than they were followdecrease being more pronounced for silently ing voicing. For the case of numbers correct, read as opposed to voiced lists, and (b) the the important interaction appeared to be that faster the presentation rate, the shorter the between Vocalization and Presentation Rate, interrecall intervals, the effect again being rather than that between Vocalization and more pronounced for R as opposed to V lists. Recall Number. Loudness of Recall. Figure 2 shows loudness DISCUSSION as a function of the main conditions, using the baseline-crossing index of loudness described From these results a broad picture of the in the Method section. Analysis of variance course of successive rehearsal emerges. (a) Reindicated a high degree of variability among call decreases in accuracy over successive reSs, this possibly arising in part from differences calls; this decrease being due to a perpetuation in the normal loudness of the various Ss’ into later recalls of errors made in the first or voices. Thus the following all yielded &values second recall, plus a few extra errors which significant at the .05 level: Vocalization x creep into each successive recall. The vocalizaRate x Ss, Recall Number x Ss, Rate x Ss, tion condition and rate of presentation affect Vocalization x Ss, Ss. But in addition, the the accuracy of the first recall, but do not difVocalization x Recall Number interaction, ferentially affect the “rate” of decrease in P(2, 68) = 10.30, p c .Ol, The Rate x Recall accuracy beyond the first recall. (b) There is a Number interaction F(4, 68) = 6.5 1, p < .Ol, monotonic association, at least for the range and the Recall Number main effect F(2,34) = of presentation rates between 1 and 3/set, be18.92, p < .Ol were significant. Figure 2 shows tween presentation rate and recall rate: fast that over successive recalls, the average loud- lists are recalled more quickly than slow lists,
MURRAY
364 160 IS0 I40 110 I20 II0 p0 g
90
gj
60
i! n”o 3 MEDIUM FAST
260 50 40
SLOW MEDIUM SLOW
30
FAST
20 IO
n
I
m
RECALL
FIG. 2. Loudness of recall as a function of vocalization condition, presentation rate, and recall number. The loudness index shown represents the number of baseline crossings, summed over all Ss, for each of the six presentation conditions; ----V; -----It.
at least on the first recall; but thereafter, successive recalls also tend to be enunciated more and more quickly; interrecall intervals also decrease. Both effects appear to be enhanced following silent reading as compared with voicing. (c) The loudness of successive recalls also decreases, particularly for silently read slow lists. The fact that the rate of decrease in number correct across successive recalls was not a function of presentation condition, suggests that, once the first recall had been given, Recall II consisted essentially of an attempt to retrieve the items recalled in I, and Recall III of an attempt to retrieve the items recalled in II. This assumption is consistent with the fact that errors tended to be of the same kind in successive recalls. Thus successive recalling is better
described as being the immediate reproduction of the immediately preceding recall than as being the repeated reproduction of the originally presented items. The increase in recall rate over successive recalls might, however, also reflect increased learning of the items correctly recalled on Recall I (see below). The finding of an increase in recall rate as presentation rate increased might also suggest that Ss recalled “parrot-fashion,” this being easiest to do at fast presentation rates where the list would more readily be apprehended as one unit. The finding of an increase in recall rate across successive recalls may reflect various factors operating in recall-increased “chunking” with each recall (as mentioned in the introduction), increasing confidence, possibly the gradual transition from a state in which S
REPEATED
RECALL
is consciously trying to retrieve the separate items from a “speech” store (cf. Sperling, 1963) to a state in which he has developed a motor habit, “rattling off” the items with little conscious effort. The decrease in loudness across recalls may simply arise from the fact that less work is involved in enunciating rapidly if the voice is kept soft as opposed to loud : alternatively, there is evidence that the faster an auditory presentation, the poorer the recall when presentation is loud as contrasted with soft (Murray, 1966~). Perhaps Ss involuntarily lower their voice when recalling rapidly, in order to reduce interference from concurrent auditory feedback. Perhaps the most important theoretical implication of the above findings is that successive recalling appears to be analogous to a sequence of learning trials in which S’s own production, the first recall-based essentially on pure short-term memory-serves as the stimulus material. The number of items correct admittedly decreased across recalls, but there were very few cases of NCC or NCC shifts (Table I), and errors made on Recall I were propagated, much as if they too were “learned”: S would have no way of knowing that they were wrong on that recall. Note that if S had been given some kind of cue regarding the correctness or incorrectness of an item in Recall I, he would have been able to change the incorrect items. It is suspected that this is the reason why the decrease over successful recalls in the present experiment did not parallel the increase in successful recalls found in experiments investigating successive recalls of lists of paired associates previously learned to a given criterion (these are reviewed by Richardson and Gropper, 1964). In the latter case, presentations of the stimulus terms may have facilitated the “unlearning” or rejection of certain responses, over successive recall trials. As Richardson and Gropper stated, this result might not have applied when the Estes RTT paradigm was used because insufficient learning trials were given prior to the recall trials;
365
IN STM
and in fact Seidel(1963) did find an increase in NC shifts across two successive recalls when the number of learning trials was increased up to five. If the above hypothesis is correct, then experiments ostensibly investigating STM, but which do permit of fairly extensive rehearsal prior to recall, might be more fruitfully considered as experiments in which S has produced his own stimulus material, from STM, and by rehearsal translated the material into LTM. REFERENCES JONES,J. E. All-or-none versus incremental learning. Psychol. Rev., 1962,69, 156-60. MURRAY, D. J. Some effects of overt response at presentation upon subsequentrecall. Ph.D. thesis on file in Cambridge University Library, 1964. MURRAY, D. J. Vocalization-at-presentation and immediate recall, with varying presentation-rates. Quart. J. exp. Psychol., 1965,17,41-S& MURRAY, D. J. Intra-list interference and rehearsal in short-term memory. Canad. J. Psychol., 1966, 20, 413-426. (a) MURRAY, D. J. Vocalization-at-presentation and immediate recall, with varying recall-methods. Quart.
J. exp. Psychol.,
1966,18,9-18.
(b)
MURRAY, D. I. Effects of loudness and presentationrate on auditory short-term memory. Nature, 1966,210,226. (c) MURRAY, D. J. Overt versus covert rehearsal in shortterm memory. Psychon. Sci., 1967,7,363%4. PETERSON,L. R., AND PETERSON,M. L. Short-term retention of individual verbal items. J. exp. Psychol., 1959,58,193-198. POSNER,M. I. Immediate memory in sequential tasks. Psychol. Bull., 1963,60,333-349. POSTMAN, L. Short-term memory and incidental learning. In A. W. Melton (Ed.), Categories of human learning. New York: Academic Press, 1964. Pp. 145-201. RICHARDSON,J., AND GROPPER,M. S. Learning during recall trials. Psychol. Rep., 1964,15,551-560. SANDERS, A. F. Rehearsal and recall in immediate memory. Ergonomics, 1961,4,25-34. SEIDEL, R. J. RTT paradigm: no panacea for theories of associative learning. Psychol Rev., 1963, 70, 565-572.
SPERLING, C. A model Human
Factors,
1963,5,
for visual memory 19-3 1.
(Received November 28,1966)
tasks.
OF VERBAL
LEARNING
AND VERBAL
Repeated
7, 358-365 (1968)
BEHAVIOR
Recall
in Short-Term
Memory’
D. J. MURRAY Queen’s
University,
Kingston,
Ontario,
Canada
Lists of eight letters were either voiced or silently read at presentation, ihe presentation rate being either 1,2, or 3 letters/set. Immediate spoken recall was then given, three times in succession. It was found that accuracy of recall decreased over successive recalls, with errors in the early recalls tending to be perpetuated over later recalls; that the rate of recall was faster for rapidly presented lists than for slowly presented lists, but also increased over successive recalls; and that the loudness of recall decreased over successive recalls. The relationships between successive recalling, postlist rehearsal, and learning are discussed with reference to these results,
When a list is memorized
for immediate recall, rehearsal can take place either during the presentation of the list, provided the presenta-
tion rate is fairly slow (Posner, 1963), or in the interval between presentation and recall (Sanders, 1961). With respect to the former, it has been shown that when intralist rehearsal is prevented by having irrelevant items interspersed among the items to be memorized, recall is reduced (Murray, 1966a); and with respect to the latter, it is known that if postlist rehearsal is prevented by asking Ss to perform a task during the interval, the reduction in recall is a direct function of the duration of the interfering activity (Peterson and Peterson, 1959). But despite the consensus that rehearsal is important, if not indeed necessary, for the retention of verbal items, there is little evidence as to what Ss actually do during rehearsal. The purpose of the present study was to obtain evidence which would at least be suggestive of events occurring during postlist rehearsal. In particular, we desired to know the extent to which errors might be perpetuated across successive recalls. If this result were obtained, it * This research was supported by N.R.C. Grant APB-126. I am extremely grateful to E. Griffiths for constructing the transducer used with the polygraph, to L. Burgoyne for assistance particularly in the collection of the data, and to H. Seth for research assistance throughout.
would suggest that successive retrievals were based on “memories” of the preceding recalls rather than upon some basic trace structure laid down at presentation. It is, of course, difficult to specify, in other than an introspective manner, how retrieval might proceed in subvocal rehearsal. But it seems reasonable to assume that, if persons are asked to recall a list several times in succession, any patterns which emerge over the course of successive vocalized recalls are likely also to be found in the case of successive subvocal rehearsal acts. This assumption has to some extent been justified by the results of a preliminary study (Murray, 1967), in which it was shown that, provided immediate recall was forced-order, no important differences in serial-position effects resulted from recall after two voiced rehearsals as opposed to two silent rehearsals. (Recall after voiced rehearsal was, however, lower than recall after silent rehearsal). In the following experiment, therefore, Ss were asked to recall immediately, aloud, several times, material which had been presented once under one of various presentation conditions. The choice of presentation conditions was determined by considerations arising from previous work. One obvious variable worthy of examination was that of presentation rate. A number of authors (see Posner’s review, 358
REPEATED RECALL IN STM
1963; and Postman, 1964) have stressed that slow presentation permits of more intralist rehearsal than does fast. However, the efficiency of recall is also a function of the nature of the responses given by S at presentation : if lists were vocalized by Ss, the advantage for recall of vocalization as opposed to silent reading was enhanced at the faster rates (Murray, 1966b). The present study therefore investigated both presentation rate and vocalization at presentation. Recall rates were also examined, partly because it had incidentally been found in earlier work that recall rates tended to parallel presentation rates (Murray, 1964, p. 147), and partly because it was felt that the process of rehearsal might involve increased “chunking,” which would be reflected in increasing recall rates across successive rehearsals. To obtain recall times in the present study, a polygraph was used: this had the advantage of also allowing recall loudness to be recorded, though no specific predictions were made as to the outcome of an analysis of this characteristic of spoken recall. It might be noted that other authors have found that successive recalls of paired associates, without feedback as to the correctness of the various recalls, have tended to increase in accuracy rather than decrease (Richardson and Gropper, 1964). Experiments using the Estes RTT paradigm have however found little evidence of shifts from incorrect to correct across successive recall trials (e.g., Jones, 1962). The present study was expected to reveal what might happen in the case of the immediate repeated recall of a list of eight letters presented just once.
359
of paper which could be fed through an arrangement of rollers above which was a viewing-slit permitting only one letter to be exposed at a time. By appropriate spacing of the items on the roll, the single letters could appear at rates of 1,2, or 3 per sec. On each roll there were 16 lists, all at the same presentation rate: a total of nine rolls was drawn up, with each of the three presentation rates being allotted three blocks of lists (see “Design”). Design. Each S worked through three rolls, one at each presentation rate. On each roll half the lists were voiced and half silently read. The orders in which Ss worked through their six conditions were counterbalanced across the experiment, apart from the restriction that the two vocalization conditions on any rate were carried out consecutively by each S. To avoid any artifacts of list difficulty, three different blocks of 16 lists were used, these blocks also being counterbalanced across conditions. Procedure. On arrival Ss were shown written instructions outlining their task, and six practice lists, one under each vocalization/presentation rate condition, werecarried out. The Sthen worked through his three rolls (48 lists). Forpresentation, Ss were instructed either to read the lists silently (without mouth movements), or voice each letter aloud as it appeared. The machine was switched off as E saw the last letter of a list pass the viewing slit. For recall, S started to recall “assoonasheliked’afterthemachinewasswitchedoff. He spoke three successive recalls into a tape recorder: the recalls were also written down by E as a further check. The S was told always to start each recall with the first presented letter and continue through to the end in order, leaving no omissions (forced-order recall). Each S’s single session lasted about 45 min. Analysis of .results. The tape recordings obtained from each S were played via a specially constructed transducer into the input of a Grass polygraph (Model SDWCl), with the sensitivity set at a constant value of 8. As each letter was sounded from the tape, this resulted in a deflection of the pen recorder on the polygraph (paper speed, 25 mm/set). This record could be used to determine (a) the timing between recalled letters and between lists, obtained by checking each deflection against a time base, and (b) the relative loudness of the spoken letters, given by the amplitude METHOD of the deflection representing each letter. To obtain General. The Ss were visually presented with lists of suitable readings, the playback intensity of the tape eight consonants for immediate recall. The letters were recorder was set for each Sso that the averagedeflection either silently read (R) or voiced (V) at presentation, of the polygraph pen was, so far as could be judged and were shown at rates of 1,2, or 3 letters/set. Recall visually, about the same for each S. Thus, despite was spoken immediately after the last letter, and three variations in the normal loudness of S’s voices as successive recalls were given (these will be denoted as compared with each other, the records were reasonably recalls I, II, III respectively). comparable between Ss, and certainly comparable Material. Lists of eight consonants, drawn from the within Ss. On all voiced trials, both S’s reading aloud pool described by Murray (1965), were typed onto rolls at presentation and his recalls were recorded on the
360
MURRAY
polygraph: on silently read trials, there was obviously no sound during presentation, but the switch-off of the memory drum made a clear signal which could be used for determining the latency between the end of presentation and the start of the first recall. Each recording was first gone through to delete any deflections due to background noises, etc. Then scores were taken of the total time required for each recalled list (from which mean time per letter could be derived), and the intervals between successive recalls. In all cases the time intervals were measured between peaks of deflections. The latency of the first recall was judged by the interval between the click caused by the switch-off of the memory drum and the start of the first recall. Finally an index of loudness was obtained for each recalled list: the index was the number of deflections per list (maximum possible, 8) which crossed the time base on the polygraph record. The more loudly a list was recalled, the more such crossings there were. More elaborate (and laborious) measures of loudness could of course be made, but we found that the results of this simple procedure were clear enough for definite conclusions to be drawn about variations in the loudness of spoken recall across successive recalls. Subjects. The Ss were 18 psychology students (mainly graduate) from Queen’s University, all of whom had had experience with memorizing using letter lists and the present apparatus (in experiments held about a year previously). They were aware that their recall was being tape recorded, but were not told
that the timing and loudness of recall were going to be examined. RESULTS
The results with respect to number
correct, timing of recalls, and loudness of recalls, will be reported separately, and then an overall picture will be given.
Number Correct. Figure 1 shows the per-
centages of letters correct (in their correct position in the list) as a function of presentation rate, voicing condition, and recall numbers (I, II, III). Analysis of variance applied to the raw data showed that there was a significant decrease
in the number
correct
across re-
calls, F(2, 68) = 70.51, p < .OOl, and a significant variation among Ss, F(17, 34) = 11.43, p < .OOl. Although when tested against the remainder, the effects of both vocalization and of presentation rate were highly significant (p < .OOl), when tested against the significant Vocalization x Rate mean square, F(2, 34) = 4.05,~ < .04, neither was significant. The interaction is shown in Fig. 1: vocalized lists were best recalled at the medium rate, and silently
?O-
I
lx
m
RECALL
FIG. 1. Percentage correct as a function ---- v;---R.
of vocalization
condition,
presentation
rate, and recall number;
REPEATED
RECALL
read lists at the slowest rate. This interaction has also been found in previous work (Murray, 1966b); in the present study, however, the Vocalization x Rate x Ss interaction was also significant, F(34, 68) = 8.49, p -c .OOl. The finding we wish to emphasize here, however, is
that as recall was repeated, there were increasing errors over successive recalls, with the rate of this increase being independent both of vocalization at presentation and of presentation rate.2 The recall data were then examined in detail to determine the nature of this increasing error TABLE PROPORTIONS
OF EACH KIND
IN
361
STM
the corresponding serial position of Recall II and that item in turn with its counterpart in
Recall III. With “CCC” used to denote that a given letter was correct across all three recalls, “NNN” to denote that it was incorrect across all three recalls, “CCN” to denote that it was correct in Recalls I and II but not in III, and so on, the percentage occurrences of all eight possible combinations were worked out (Table 1). Apart from a higher frequency of NNN cases following silent reading as opposed to voicing -as would be expected, given the data shown in Fig. l-there were no apparent differences 1
OF ERROR SHIFT OVER THE THREE RECALLS CONDITIONS
UNDER THE
SIXPRESENTATION
Presentationconditions Vocalization rate
V 1
ccc
.350
CCN
.051
CNC
.008 .075 .015 .017 .016 .469
CNN NCC NCN NNC NNN
R
2
3
1
2
3
Mean
.418 a43 .017 .082 .017 .012 .021 .391
.334 .051 .015 .120 .022 .016 .012 .431
,333 .027 1.00 .049 .OlO .009 .007 .553
.303 a45 .008 .060 ,012 .007 .012 .553
.271 .029 .009 .048 .016 .005 .012 .610
.305
rate across recalls. Each separate letter in
Recall I was compared with its counterpart in ZIt might be asked whether the decreasein performance over successiverecalls was related to any proactive inhibition effects accumulating over the session.If the sessionswere divided into thirds (16 lists each), the decreaseover successiverecallsshowed up clearly for each third of the session. Moreover, performance improved, rather than decreased,over the whole session.Given that the conditions were counterbalanced over session-thirds,it thus seems doubtful that the validity of the above resultswould be affectedby PI artifacts. It wasnoted, however,that for the veryfirst list, 12out of the 18Ss did equally well on all three recalls.It may have been that PI effectswere operative over the first few listsof the sessiononly.
.041 .012 .072 .015 .OOl .013 .501
of importance between Rand V with respect to the different types of combination. Essentially, Table 1 shows that an item correct on recall I had a high probability of being correct on Recall II and III, while items incorrect
on
Recall I were likely to stay incorrect on Recalls II and III. The overall downtrend in number correct across successive recalls is reflected in
the incidence of CCC, CNN, and CCN cases, respectively. This analysis does not tell us, however, whether an error in Recall I will be perpetuated throughout Recalls II and III, or whether the error will change (i.e., if “B” is wrongly
362
MURRAY
TABLE
2
ANALYSIS OF NNN (PROPORTIONS
OF ERROR
PRESERVATIONS
CASES AND ERROR
Between recalls I and II Proportions of errors which were:
Changed
Preserved
Changed
V
1 2 3
.657 .626 .568
.343 .374 .432
.712 .728 .731
.288 .272 .269
R
1 2 3
.719 .686 .707
.281 .314 .293
.813 .777 .748
.187 .223 .252
times per recall and on the interrecall intervals (the latter including the interval between machine switch-off and the start of the first recall). On times per recall, there was a significant Vocalization x Rate x 5’s interaction, F(34, 68) = 4.01, p < .Ol. Significant two-way interactions were found for Recall Numbers x Ss, F(34,68) = 1.83, p < .05, and for Vocalization x Recall Number, F(2, 68) = 6.46, p -C.Ol. In the latter case, while later recalls were consistently shorter than were earlier recalls, the
TABLE RECALL
TIMES
Between recalls II and III
Preserved
recalled as 7” on Recall I, will it also be recalled as “V” on Recall II, or as some other letter?). Table 2 shows an analysis of NNN cases for each of the six main conditions: it can be seen that, for all conditions, the probability of an error’s being perpetuated across all three recalls was at least double that of its being changed from recall to recall. Timing of Recall. Table 3 shows the mean times per recall and mean interrecall intervals obtained under the main conditions. Separate analyses of variance were carried out on the
MEAN
CHANGES)
AND INTERRECALL
INTERVALS
3
FOR RECALLS CONDITIONS
Recall times (set) Presentation rate (item/@
I, II,
AND
Interrecall
III
UNDER
THE SIX PRESENTATION
intervals (xc)
I
II
III
I
I-II
II-III
R
1 2 3
5.88 5.32 4.57
4.32 3.94 3.99
4.25 3.79 3.69
2.06 2.05 1.75
1.59 1.55 1.38
1.38 1.41 1.19
V
1 2 3
5.25 4.25 4.03
4.49 4.06 3.74
4.20 3.66 3.56
1.91 1.34 1.31
1.38 1.25 1.31
1.57 1.46 1.45
4.88
4.09
3.86
1.74
1.41
1.41
Mean
REPEATED
RECALL
IN STM
363
difference was most marked for silently read ness of each recall decreased, the effect being lists as opposed to voiced lists. As a conse- more marked for R than for V lists, and for quence of this interaction, the main effects of slow than for medium or fast lists. Interrelationships Between Number Correct, neither vocalization nor of recall were signifiRecall-Time, and Recall-Loudness. Although cant, but it is clear from Table 3 that time per the above results appear complicated, there recall decreased across successive recalls. The are a number of common threads that can be effect of presentation rate upon recall rate was significant, however, F(2, 34) = 8.50, p < .Ol : teased out from the mass. First, in all measures, the faster the presentation rate, the more rapid save that of time per recall, there was a signifithe first, and subsequent, recalls. This is the cant three-way interaction of Vocalization, Rate, and Ss. This can be taken to indicate that most obvious feature shown in Table 3. The analysis of interrecall intervals showed there are large individual differences in the a large number of interactions significant at degree to which persons found vocalization at the .05 level and less: Vocalization x Recall presentation affecting their recall following any Number, F(2, 68) = 15.99; Vocalization x particular presentation rate. Second, on all Rate, F(2, 68) = 3.66; Vocalization x Ss, analyses save that of number correct, Recall F(17, 68) = 2.02; Recall Number x Ss, F(34, Number x Ss interactions were significant; 68) = 2.92; and Rate x Ss, F(34, 68) = 2.10. thus there was a high degree of concordance When the main effects were tested against among Ss with respect to the decrease in these interactions, only the Ss factor yielded a number correct over successive recalls, but significant variance ratio, F( 17, 34) = 22.9, less concordance with respect to other trends over successive recalls. And third, for all p < .Ol. Many of these interactions merely reflected subject variability. The most imporanalyses except that of numbers correct, trends tant results seemed to be that (a) interrecall over successive recalls were more marked intervals decreased over successive recalls, the following silent reading than they were followdecrease being more pronounced for silently ing voicing. For the case of numbers correct, read as opposed to voiced lists, and (b) the the important interaction appeared to be that faster the presentation rate, the shorter the between Vocalization and Presentation Rate, interrecall intervals, the effect again being rather than that between Vocalization and more pronounced for R as opposed to V lists. Recall Number. Loudness of Recall. Figure 2 shows loudness DISCUSSION as a function of the main conditions, using the baseline-crossing index of loudness described From these results a broad picture of the in the Method section. Analysis of variance course of successive rehearsal emerges. (a) Reindicated a high degree of variability among call decreases in accuracy over successive reSs, this possibly arising in part from differences calls; this decrease being due to a perpetuation in the normal loudness of the various Ss’ into later recalls of errors made in the first or voices. Thus the following all yielded &values second recall, plus a few extra errors which significant at the .05 level: Vocalization x creep into each successive recall. The vocalizaRate x Ss, Recall Number x Ss, Rate x Ss, tion condition and rate of presentation affect Vocalization x Ss, Ss. But in addition, the the accuracy of the first recall, but do not difVocalization x Recall Number interaction, ferentially affect the “rate” of decrease in P(2, 68) = 10.30, p c .Ol, The Rate x Recall accuracy beyond the first recall. (b) There is a Number interaction F(4, 68) = 6.5 1, p < .Ol, monotonic association, at least for the range and the Recall Number main effect F(2,34) = of presentation rates between 1 and 3/set, be18.92, p < .Ol were significant. Figure 2 shows tween presentation rate and recall rate: fast that over successive recalls, the average loud- lists are recalled more quickly than slow lists,
MURRAY
364 160 IS0 I40 110 I20 II0 p0 g
90
gj
60
i! n”o 3 MEDIUM FAST
260 50 40
SLOW MEDIUM SLOW
30
FAST
20 IO
n
I
m
RECALL
FIG. 2. Loudness of recall as a function of vocalization condition, presentation rate, and recall number. The loudness index shown represents the number of baseline crossings, summed over all Ss, for each of the six presentation conditions; ----V; -----It.
at least on the first recall; but thereafter, successive recalls also tend to be enunciated more and more quickly; interrecall intervals also decrease. Both effects appear to be enhanced following silent reading as compared with voicing. (c) The loudness of successive recalls also decreases, particularly for silently read slow lists. The fact that the rate of decrease in number correct across successive recalls was not a function of presentation condition, suggests that, once the first recall had been given, Recall II consisted essentially of an attempt to retrieve the items recalled in I, and Recall III of an attempt to retrieve the items recalled in II. This assumption is consistent with the fact that errors tended to be of the same kind in successive recalls. Thus successive recalling is better
described as being the immediate reproduction of the immediately preceding recall than as being the repeated reproduction of the originally presented items. The increase in recall rate over successive recalls might, however, also reflect increased learning of the items correctly recalled on Recall I (see below). The finding of an increase in recall rate as presentation rate increased might also suggest that Ss recalled “parrot-fashion,” this being easiest to do at fast presentation rates where the list would more readily be apprehended as one unit. The finding of an increase in recall rate across successive recalls may reflect various factors operating in recall-increased “chunking” with each recall (as mentioned in the introduction), increasing confidence, possibly the gradual transition from a state in which S
REPEATED
RECALL
is consciously trying to retrieve the separate items from a “speech” store (cf. Sperling, 1963) to a state in which he has developed a motor habit, “rattling off” the items with little conscious effort. The decrease in loudness across recalls may simply arise from the fact that less work is involved in enunciating rapidly if the voice is kept soft as opposed to loud : alternatively, there is evidence that the faster an auditory presentation, the poorer the recall when presentation is loud as contrasted with soft (Murray, 1966~). Perhaps Ss involuntarily lower their voice when recalling rapidly, in order to reduce interference from concurrent auditory feedback. Perhaps the most important theoretical implication of the above findings is that successive recalling appears to be analogous to a sequence of learning trials in which S’s own production, the first recall-based essentially on pure short-term memory-serves as the stimulus material. The number of items correct admittedly decreased across recalls, but there were very few cases of NCC or NCC shifts (Table I), and errors made on Recall I were propagated, much as if they too were “learned”: S would have no way of knowing that they were wrong on that recall. Note that if S had been given some kind of cue regarding the correctness or incorrectness of an item in Recall I, he would have been able to change the incorrect items. It is suspected that this is the reason why the decrease over successful recalls in the present experiment did not parallel the increase in successful recalls found in experiments investigating successive recalls of lists of paired associates previously learned to a given criterion (these are reviewed by Richardson and Gropper, 1964). In the latter case, presentations of the stimulus terms may have facilitated the “unlearning” or rejection of certain responses, over successive recall trials. As Richardson and Gropper stated, this result might not have applied when the Estes RTT paradigm was used because insufficient learning trials were given prior to the recall trials;
365
IN STM
and in fact Seidel(1963) did find an increase in NC shifts across two successive recalls when the number of learning trials was increased up to five. If the above hypothesis is correct, then experiments ostensibly investigating STM, but which do permit of fairly extensive rehearsal prior to recall, might be more fruitfully considered as experiments in which S has produced his own stimulus material, from STM, and by rehearsal translated the material into LTM. REFERENCES JONES,J. E. All-or-none versus incremental learning. Psychol. Rev., 1962,69, 156-60. MURRAY, D. J. Some effects of overt response at presentation upon subsequentrecall. Ph.D. thesis on file in Cambridge University Library, 1964. MURRAY, D. J. Vocalization-at-presentation and immediate recall, with varying presentation-rates. Quart. J. exp. Psychol., 1965,17,41-S& MURRAY, D. J. Intra-list interference and rehearsal in short-term memory. Canad. J. Psychol., 1966, 20, 413-426. (a) MURRAY, D. J. Vocalization-at-presentation and immediate recall, with varying recall-methods. Quart.
J. exp. Psychol.,
1966,18,9-18.
(b)
MURRAY, D. I. Effects of loudness and presentationrate on auditory short-term memory. Nature, 1966,210,226. (c) MURRAY, D. J. Overt versus covert rehearsal in shortterm memory. Psychon. Sci., 1967,7,363%4. PETERSON,L. R., AND PETERSON,M. L. Short-term retention of individual verbal items. J. exp. Psychol., 1959,58,193-198. POSNER,M. I. Immediate memory in sequential tasks. Psychol. Bull., 1963,60,333-349. POSTMAN, L. Short-term memory and incidental learning. In A. W. Melton (Ed.), Categories of human learning. New York: Academic Press, 1964. Pp. 145-201. RICHARDSON,J., AND GROPPER,M. S. Learning during recall trials. Psychol. Rep., 1964,15,551-560. SANDERS, A. F. Rehearsal and recall in immediate memory. Ergonomics, 1961,4,25-34. SEIDEL, R. J. RTT paradigm: no panacea for theories of associative learning. Psychol Rev., 1963, 70, 565-572.
SPERLING, C. A model Human
Factors,
1963,5,
for visual memory 19-3 1.
(Received November 28,1966)
tasks.