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Distance between related words in free recall: Trace of the STS
JOURNAL OF VERBALLEARNINGAND VERBALBEHAVIOR8, 105--111 (1969)
Distance between Related Words in Free Recall: Trace of the STS1 MURRAY GLANZER2 New York University, New York, New York 10003
Two experiments on free recall are presented in which pairs of related words are presented within the lists and the number of words intervening between the related pair is systematically varied. In Exp. I the relation was a mnemonic, or associative, relation. In Exp. II the relation was repetition. A second variable in both experiments was presentation rate. In both experiments, systematic, monotonic effects of the number of intervening items were found. The relevance of the effects to a model that postulates two distinct storage mechanisms--an STS and LTS--is discussed.
The model for free recall used here is based on the assumption of two distinct storage m e c h a n i s m s - - a short-term store (STS) and a long-term store (LTS). Verbal units first enter STS and are held there temporarily. Eventually, the units either enter LTS or are forgotten. Several investigators have discussed this general type of model (Atkinson and Shiffrin, in press; Glanzer and Cunitz, 1966; Murdock, 1967; Peterson, 1966; Waugh and N o r m a n , 1965). The STS is assumed here to function as an input buffer that holds a limited amount of recent input information and keeps it available for various operations required by the task set for S. I f S makes use of relations between successive input items while they are in STS, then certain systematic changes in recall should occur as a function of distance between the items. This statement will be expanded below. In the first study, the relation between successive input words is mnemonic. In the second study, the relation between the successive words is that of repetition.
EXPERIMENT I: MNEMONIC STRUCTURE, NUMBER OF INTERVENING ITEMS AND PRESENTATION RATE
Mnemonic structure is defined here as any relation between a pair of words that facilitates the acquisition of one, given the other. Although association norms are used here to select pairs that have mnemonic structure, other bases of selection could be used--e.g., logical, semantic, or phonemic relations. There is evidence that mnemonic structure increases free recall (Cohen, 1963; Deese, 1959; Glanzer and Meinzer, 1967). The question arises as to when and how the mnemonic structure of a list has its effect as the list information progresses through the STS-LTS system. One assumption is that the list's mnemonic structure has its effect while the list items are in STS. The STS, however, holds relatively few words--three to six--these primarily the most recently presented words. The later the second member of a mnemonically related pair follows the first member, the less likely that the 1 This investigation was supported by the U. S. Army first member will still be present in STS. This Medical Research and Development Command, implies that the more closely two related words Department of the Army, under Research Contract follow each other, the more likely that their DA-49-193-MD-2496. 2 The author thanks Steven Dubin, Rosamond relation will have an effect. There are data Gianutsos, Deborah Lhamon, and Ronald Murphy (Mayzner and Tresselt, 1961) to support this assertion of a systematic distance f u n c t i o n - for their help in collecting and analyzing the data. 105
106
GLANZER
that the greater the distance between m n e m o nically related words, the lower the p r o b a b i l i t y of recall. Distance between a pair of words can m e a n several things. It can m e a n the n u m b e r of items that intervene between the related words. It can also m e a n the a m o u n t of time that elapses between the related items. These two variables can be m a n i p u l a t e d independently. I n the present study, b o t h n u m b e r of items between related words a n d the p r e s e n t a t i o n rate will be varied. O n the basi s of earlier findings (Mayzn e t a n d Tresselt, 1961; G l a n z e r a n d Cunitz, 1966) it was expected that these two variables would have opposed effects. Increasing the n u m b e r of i n t e r v e n i n g words should reduce the effect of m n e m o n i c structure a n d therefore decrease the n u m b e r of words recalled. I n creasing the time interval between successive words should increase the n u m b e r of words recalled. The m a i n d e p e n d e n t variable here will be the total n u m b e r of words recalled.
Method Each S was given two sets of free recall lists, with four lists in each set. One set was given at a fast rate, with a 1-sec interval between successive words. The other set was given at a slow rate, with a 3-sec interval between words. The four lists within each set were composed of mnemonicallyrelated pairs of words. The distance between the pair members was systematically varied across the four lists. Materials. The words used for the lists were drawn from 64 pairs of nouns described by Glanzer and Meinzer (1967). Each pair consisted of a KentRosanoff stimulus word and one of its low-frequency associates, i.e., a word given by fewer than 3 ~ of the Russell-Jenkins norm group (Russell and Jenkins, 1954). Word association was therefore used to define mnemonic relation here. Low-frequency associates were used to minimize the opportunity for Ss to use some associative strategy rather than recall of the specific list words presented. They were also used to minimize ceiling effects in the data. Four types of lists were constructed. Each list consisted of eight pairs of associated words. The lists differed in the number of words interveningbetween the members of each pair--the distance between pair members. Distance 0. The pair members were immediately adjacent: Stove, coal, ankle, foot, etc. Distance 1. The
two words of a pair were separated from each other by one word, a member of another pair: Stove, ankle, coal, foot, etc. Distance 3. Three intervening words: Stove, ankle, parent, alcohol, coal, foot, child, whiskey, etc. Distance 7. Seven intervening words: Stove, ankle,
parent, alcohol, pasture, wish, bread, nest, coal, foot, child, whiskey, etc. Word pairs were assigned to and ordered within each list randomly. The ordering within each pair was also randomized so that the Kent-Rosanoff stimulus word preceded its associate in half the pairs and followed it in the others. The ordering ofthelist types was randomized independentlyfor each S. Each S thus had an independently randomized sequence of lists and sequence of words within lists. In addition to the experimental lists, there were four practice lists; two of four words each and two of 16 words each. The words in the practice lists were 40 nouns of Thorndike-Lorge AA frequency (Thorndike and Lorge, 1944). They were also assigned and ordered at random, independently for each S. Apparatus. The stimuli were shown with a slide projector. The exposure times and the intervals between words were controEed by a Gerbrands programmer modified to run at 15 rpm. Subjects. The Ss were 70 college students who were paid for participating. Procedure. Each S was run individually.He was first shown a four-word practice list, a 16-word practice list and then the four main lists at one rate. Then he was told that the rate would be changed and was given another sequence of two practice lists and four main lists at the other rate. Half of the Ss had the 1-sec interval lists first. Half had the 3-secintervallistsfirst. All words were exposed for 1 sec. The S said each word aloud when it appeared on the screen. After each 16-word list, S was given 90 sec to write his responses in a booklet.
Results The curves in Fig. 1 summarize the overall results. W i t h a n increase in i n t e r v e n i n g items between related words there is a drop in m e a n p r o p o r t i o n of recall from .771 to .671 per word in the 3-sec rate a n d from .730 to .592 on the 1-sec rate. Both curves decline m o n o t o n i c a l l y b u t the shapes of the two curves differ. Analysis of variance was carried out with order, i.e., fast rate first vs. slow rate first, as a between-S variable a n d n u m b e r of i n t e r v e n i n g items, rate a n d serial position as w i t h i n - S variables. The m a i n effect of order was n o t significant F < 1. The m a i n effects of n u m b e r o f intervening items, F(3, 2 0 4 ) = 3 5 . 3 2 ; rate,
DISTANCE IN FREE RECALL
.8O (~ .75 o
u
. 70
~
.65
0 a:
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3SEC
1 SEC ,,o I
I
I
0
1
2
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3 4 DISTANCE
I
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FIG. 1. P r o p o r t i o n s o f associated w o r d s recalled at 1- a n d 3-sec p r e s e n t a t i o n rates as a f u n c t i o n of n u m b e r
of words between the pair members (distance). F(1, 68)= 67.03, and serial position, F(15, 1020)=34.54 were all highly significant, p < .001. The use of conservative tests (Greenhouse and Geisser, 1959) does not alter the significance levels of the findings. Only one of the interactions involving the main variables attains significance--the interaction of number of intervening items and rate, F(3, 204) = 2.64, p < .05. A conservative test of this effect, rising reduced degrees of freedom, does not leave this significant. Examination of the serial position curves for the individual experimental conditions reveals patterns similar to those found before. The double peaked serial position curves are found over all conditions. There is only- one interaction with serial position that is indicated by the data--the interaction of rate with serial position. The curves for the 3-sec rate and the 1-sec rate are clearly separate except that they merge in the last three positions. This agrees with earlier findings (Glanzer and Cunitz, 1966; Murdock, 1962). The interaction for serial position and rate was, however, not significant, F(15, 1020) = 1.65, .05 < p <.10. There is not even a suggestion of interaction between numbers of intervening items and serial position. Discussion
The effect of the number of intervening words fits the picture of a limited-capacity STS
107
discussed in preceding work. The data show that the probability of recall of mnemonically related words is a declining function of the number of words separating them. The interpretation of this function is that the probability that both members of a related pair will be in STS at the same time declines with the number of words separating the pair. As each intervening word enters, the probability increases that the first member of the pair will leave STS. If the first member of the pair has left STS, then the facilitative effect of the mnemonic relation between the words does not occur. The curves in Fig. 1 are then a function of the decline in probability of a word being in STS with each successive new word. The curves are, however, not a simple function of that decline in probability. They reflect a summation of probabilities over several successive inputs. The curves show, moreover, that the effects are not simply due to the passage of time. The effect of increasing inter-item interval is the opposite of that of increasing the number of items between pairs. It increases the total amount recalled. Thus, the STS is limited with respect to number of items it holds, not the amount of time it holds them. The lack of any marked difference between the serial position curves for the two rates and for the four interval conditions, permits averaging across all serial positions as in Fig. 1. The evidence for the lack of a difference is the nonsignificant Fs for the interaction of serial position with number of intervening items and with rate. The absence of interaction of number of intervening items with serial position is in line with data indicating the absence of interaction of presenc e vs. absence of mnemonic structure with serial position (Glanzer and Meinzer, 1967). The absence of an interaction indicates that the mnemonic structure has its effect while the words are in STS, making rehearsal in STS more efficient. An increase in efficiency of rehearsal also increases the probability that the words will be registered in LTS. Thus the effects of mnemonic structure would appear in both STS and LTS
108
GLANZER
and therefore across all serial positions. I f the m n e m o n i c structure affected only the probability o f registration in LTS, then the separation of the serial position curves should hold for all but the last few positions, the positions identified with output f r o m STS. The absence of a significant interaction between presentation rate and serial position seems to run contrary to previous findings (Gianzer and Cunitz, 1966; M u r d o c k , 1962). I n those studies, differences in rate affect all but the last few positions in the serial position curve. Examination o f the serial position curves indicates that the same effects are present in the present data. The interaction test is not specific and therefore, in this case, conservative. Analysis o f the difference between the 3- and 1-see means for the first four positions finds a highly significant F(1, 6 8 ) = 26.40, p < .001 ; for the last four positions, however, F(1, 68) = 1.81, p > .10. The merging o f the last few positions in the serial position curve occurs here as previously. The effect is, however, a small one in this experiment. EXPERIMENT I I : REPETITION, NUMBER OF INTERVENING ITEMS AND PRESENTATION RATE Repeating an item within a free recall list can, depending on the experimental conditions, lower recall (Glanzer and Meinzer, 1967), or raise recall (Waugh, 1962, 1963). The experiments cited above differed in a n u m b e r of ways so that it is not possible, on the basis o f those experiments, to specify a single variable to account for the differences. One variable, however, should be i m p o r t a n t - - t h e distance between repetitions o f a list word. W h e n words in a free-recall list are repeated, the repetition can occur while the first representation is still in STS or after it has left STS. I f the first representation has left STS, then it would be reasonable to view the S as being given two independent trials to learn that word. If, however, the second representation enters STS while the first is still there, several possibilities seem reasonable. T w o will be considered here: (a) The two representations are processed
independently as they are when they are in STS at different times; (b) the two representations are processed as a single representation. The first alternative implies that change in the distance between repetitions of a w o r d will have no effect. There are some data (Waugh, 1963) that support the first alternative. Other data indicate that distance does have an effect (Peterson, Wampler, Kirkpatrick, and Saltzman, 1963; Melton and Shulman, 1967). Some data (Glanzer and Cunitz, 1966) indicate that repeated presentation o f words in immediate succession gives no better performance than leaving empty a period o f time equal to that used for repetition, i.e., equivalent spacing. Three immediately successive repetitions gave no better recall than one presentation over the same time interval. These data would lend support to the second alternative. Method Parallel to Exp. I, both the number of words intervening between the repeated words and the presentation rate were varied. Each S was given 13 free recall
lists at either a fast rate, 1-see interval between words-or a slow rate, 3-see interval. Each list consisted of 16 words--12 different words, four of which were repeated once. The apparatus and general procedure were the same as in Exp. I. Materials. The words used for all lists were drawn from a set of 220 monosyllabic AA (Thorndike and Lorge, 1944) nouns. In each word list, there were four repeated words, in the following conditions: Distance 0, no intervening items; Distance 1, one intervening item; Distance 2; and Distance 5. The intervening items could be either nonrepeated words or words from repetition pairs. Repetition pairs were assigned at random to positions in the list with the following restrictions. Each repetition condition occurred no more than twice within a single list. Across the 13 lists, each repetition condition appeared once and only once at each possible serial position. Since each list consisted of 16 positions or items, there were 16 positions at which unrepeated items could appear, 15 at which zero-interval repetitions could appear, 14 at which one-interval repetitions could appear, etc. In addition to the 13 main lists there were two practice lists, of the same length and structure as the main lists. Twenty-five different sets of lists were generated by independent randomization. Within each randomization, three Ss were given the lists at the 1-see rate and three Ss were given the lists at a 3-see rate.
DISTANCE IN FREE RECALL
Subjects. The Ss were 150 introductory psychology students who participated in fulfillment of a course requirement. Procedure.The only major differencein the procedure from Exp. I was that S was shown lists at only one presentation rate, either 1 or 3 sec. Results The curves in Fig. 2 summarize the overall results. There is an increase in the probability of recall with repetition. The effect of repetition depends on the number of intervening words, increasing monotonically with that number.
109
or the second presentation of the word, or both. To estimate the proportion of correct recalls that S should have if he had two independent trials with the word, the following computation was carried out, using the mean proportion of recalls of unrepeated words at equivalent serial positions. Estimated p =Pi + Pi+d+X --Pi'P~+d+ l, where i is the same serial position as the first member of a pair and d the distance condition. For example, the mean proportions of recalls of unrepeated words at a 1-sec rate for posi-
.90 .85 .BO ................. o
.75 .70 .65 .60 .55 .50 I
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FIG. 2. Proportions of repeated words recalled at 1- and 3-sec presentation rates as a function of number of words between the repeated words (distance). Also shown on the solid lines are the proportions for unrepeated words (N). The estimated proportionsfor two independent trials are shown on the broken lines.
Analysis of variance was carried out with rate as a between-S variable and repetition condition as a within-S variable. The main effect of both variables was highly significant-rate, F(1, 148) = 43.51, p < .001, and repetition condition, F(4, 592) = 110.20, p < .001. The interaction between repetition condition and rate was not significant, F(4, 592) = 1.56, p > .10. T o evaluate fully the gains made by S with repeated presentation of a word, some additional information is necessary. The S may be viewed as recalling a repeated word on the basis of either the first presentation of the word,
tions 1, 2, and 3 across the lists are .69, .56, and .53. An estimated proportion for a repeated word at Distance 0, Serial Positions 1 and 2 would be .69 + .56 - .39 = .86. An estimated proportion for a repeated word at Distance 1, Serial Positions 1 and 3 would be .69 + .53 .37 = .85. The mean of the estimated values obtained in this fashion was taken across all serial positions. Those means are plotted on the broken line in Fig. 2. The estimated values stay constant for all conditions except Distance 5, which rises. Because of the shape of the serial position curve, high and lowp's are being combined for Distance 5, rather than similar
110
GLANZER
values as in Distance 0, 1, or 2. The effect of combining very different p's is to give a higher overall mean. As can be seen in the figure, the mean performance under each distance condition falls below that estimated for two independent tries at the word in all conditions except Distance 5. Tests of the deviations of the obtained values from the theoretical values find that all distances except Distance 5 differ significantly, p < .05, from the corresponding estimated values. Serial position curves for the nonrepeated words were plotted for the 1- and 3-sec rates. The curves display the effects found previously --separation at all but the last few positions. In these data the curves clearly merge from positions 12 through 16.
Discussion
respect to Exp. II, it could be argued that the effect of increasing distance of the repetitions is due to the placement of the two presentations in different contexts. Thus, a repetition at Distance 0 gives the repeated word only two neighboring items. A repetition at Distance 2 gives it four different neighboring items. If associations are formed with the neighboring items and those items function as retrieval cues, then an increase in recall would be expected. This approach would have to be developed further to explain the difference between Distance 2 and 5. If the development defines neighboring items as those three or four or five positions away, then a rationale for this definition would have to be constructed. The STS is the idea used here to rationalize these effects. The curves displayed in Figs. 1 and 2 are considered in this interpretation as traces of STS. REFERENCES
Again the effect of the number of intervening ATKINSON,R. C., AND Ssr~rmN, R. M. Mathematical models for memory and learning. In D. P. Kimble words fits the picture of a limited-capacity STS. (Ed.), The proceedings of the third conference on As the distance between the first and second learning, remembering and forgetting. New York: presentation of an item increases, so that it is New York Academy of Sciences, in press. less likely that the two representations of the COHEN, B. H. Recall of categorized word lists. J. exp. Psychol., 1963, 66, 227-234. item co-occur in STS, there is a closer approximation to the recall expected on the basis of DEES~, J. Influence of inter-item associative strength upon immediate free recall. Psychol. Rep., 1959, two independent trials. 5, 305-312. In preceding work (Glanzer and Cunitz, GLANZER,M., ANDCUNITZ, A. R. Two storage mech1966; Glanzer and Meinzer, 1967) the shape of anisms in free recall. J. verb. Learn. verb. Behav., 1966, 5, 351-360. the serial position curve was the dependent variable used to analyze characteristics of GLANZER,M., AND MEINZER,A. The effects of intralist activity on free'recall. J. verb. Learn. verb. Behav., STS. Here the serial position curve was not 1967, 6, 928-935. used in this way. With pairs of words under GREENHOUSE,S. W., AND GEISSER,S. On the methods study, the specification of the locus of an effect in the analysis of profile data. Psychometrika, 1959, 24, 95-112. in the serial order becomes less clear. The two major variables considered in Exps. I and II MAYZN~R, M. S., AND "I~.ESSELTI M. E. Incidental learning: A function of associative strength and do not, moreover, lend themselves to such distance between S-R pairs. J. Psychol., 1962, 53, analysis. Repetition distance, for example, does 155-160. not permit comparison of serial position curves MELTON,A. W., AND SHULMAN,H. G. Further studies of a distributed practice effect on probability of since the number of possible positions varies recall in free recall. Paper read at Psychonomic with distance. On a 16-item list there are 15 Society meeting, September, 1967. positions for pairs at Distance 0, and only 10 MURDOCK, B. B., JR. The serial position effect in free positions at Distance 5. recall. J. exp. Psychol., 1962, 64, 482-488. There are, of course, other ways of viewing MtmoocK, B. B., JR. Recent developments in shortterm memory. Brit. J. Psychol., 1967, 58, 421-433. the results obtained in Exps. I and II. With
DISTANCE IN FREE RECALL
PETERSON,L. R. Short-term verbal memory and learning. Psychol. Rev., 1966, 73, 193-207. PETERSON,L. R., WAMPLER,R., KIRKPATRICK,M., AND SALTZMAN,D. Effect of spacing presentations on retention of a paired associate over short intelvals. J. exp. Psychol., 1963, 66, 206-209. RUSSELL, W. A., AND JENKINS, J. J. The complete Minnesota norms for responses to 100 wordsfrom the Kent-Rosanoff Association Test.- ONR Tech. Rep. No. 11, 1954. TrIORNDIKE, E. L., AND LORGE, I. The teacher's word book of 30,000 words. New York: Bureau of
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Publications, Teacher's College, Columbia University, 1944. WAUCH, N. C. Immediate memory as a function of repetition. J. verb. Learn. verb. Behav., 1963, 2, 107-112. WAUGH,N. C. The effect of intralist repetition on free recall. J. verb. Learn. verb. Behav., 1962, 1, 95-99. WAUOH,N. C., AND NOR~tAN,D. A. Primary memory. Psychol. Rev., 1965, 72, 89-104. (Received May 31, 1968)
Distance between Related Words in Free Recall: Trace of the STS1 MURRAY GLANZER2 New York University, New York, New York 10003
Two experiments on free recall are presented in which pairs of related words are presented within the lists and the number of words intervening between the related pair is systematically varied. In Exp. I the relation was a mnemonic, or associative, relation. In Exp. II the relation was repetition. A second variable in both experiments was presentation rate. In both experiments, systematic, monotonic effects of the number of intervening items were found. The relevance of the effects to a model that postulates two distinct storage mechanisms--an STS and LTS--is discussed.
The model for free recall used here is based on the assumption of two distinct storage m e c h a n i s m s - - a short-term store (STS) and a long-term store (LTS). Verbal units first enter STS and are held there temporarily. Eventually, the units either enter LTS or are forgotten. Several investigators have discussed this general type of model (Atkinson and Shiffrin, in press; Glanzer and Cunitz, 1966; Murdock, 1967; Peterson, 1966; Waugh and N o r m a n , 1965). The STS is assumed here to function as an input buffer that holds a limited amount of recent input information and keeps it available for various operations required by the task set for S. I f S makes use of relations between successive input items while they are in STS, then certain systematic changes in recall should occur as a function of distance between the items. This statement will be expanded below. In the first study, the relation between successive input words is mnemonic. In the second study, the relation between the successive words is that of repetition.
EXPERIMENT I: MNEMONIC STRUCTURE, NUMBER OF INTERVENING ITEMS AND PRESENTATION RATE
Mnemonic structure is defined here as any relation between a pair of words that facilitates the acquisition of one, given the other. Although association norms are used here to select pairs that have mnemonic structure, other bases of selection could be used--e.g., logical, semantic, or phonemic relations. There is evidence that mnemonic structure increases free recall (Cohen, 1963; Deese, 1959; Glanzer and Meinzer, 1967). The question arises as to when and how the mnemonic structure of a list has its effect as the list information progresses through the STS-LTS system. One assumption is that the list's mnemonic structure has its effect while the list items are in STS. The STS, however, holds relatively few words--three to six--these primarily the most recently presented words. The later the second member of a mnemonically related pair follows the first member, the less likely that the 1 This investigation was supported by the U. S. Army first member will still be present in STS. This Medical Research and Development Command, implies that the more closely two related words Department of the Army, under Research Contract follow each other, the more likely that their DA-49-193-MD-2496. 2 The author thanks Steven Dubin, Rosamond relation will have an effect. There are data Gianutsos, Deborah Lhamon, and Ronald Murphy (Mayzner and Tresselt, 1961) to support this assertion of a systematic distance f u n c t i o n - for their help in collecting and analyzing the data. 105
106
GLANZER
that the greater the distance between m n e m o nically related words, the lower the p r o b a b i l i t y of recall. Distance between a pair of words can m e a n several things. It can m e a n the n u m b e r of items that intervene between the related words. It can also m e a n the a m o u n t of time that elapses between the related items. These two variables can be m a n i p u l a t e d independently. I n the present study, b o t h n u m b e r of items between related words a n d the p r e s e n t a t i o n rate will be varied. O n the basi s of earlier findings (Mayzn e t a n d Tresselt, 1961; G l a n z e r a n d Cunitz, 1966) it was expected that these two variables would have opposed effects. Increasing the n u m b e r of i n t e r v e n i n g words should reduce the effect of m n e m o n i c structure a n d therefore decrease the n u m b e r of words recalled. I n creasing the time interval between successive words should increase the n u m b e r of words recalled. The m a i n d e p e n d e n t variable here will be the total n u m b e r of words recalled.
Method Each S was given two sets of free recall lists, with four lists in each set. One set was given at a fast rate, with a 1-sec interval between successive words. The other set was given at a slow rate, with a 3-sec interval between words. The four lists within each set were composed of mnemonicallyrelated pairs of words. The distance between the pair members was systematically varied across the four lists. Materials. The words used for the lists were drawn from 64 pairs of nouns described by Glanzer and Meinzer (1967). Each pair consisted of a KentRosanoff stimulus word and one of its low-frequency associates, i.e., a word given by fewer than 3 ~ of the Russell-Jenkins norm group (Russell and Jenkins, 1954). Word association was therefore used to define mnemonic relation here. Low-frequency associates were used to minimize the opportunity for Ss to use some associative strategy rather than recall of the specific list words presented. They were also used to minimize ceiling effects in the data. Four types of lists were constructed. Each list consisted of eight pairs of associated words. The lists differed in the number of words interveningbetween the members of each pair--the distance between pair members. Distance 0. The pair members were immediately adjacent: Stove, coal, ankle, foot, etc. Distance 1. The
two words of a pair were separated from each other by one word, a member of another pair: Stove, ankle, coal, foot, etc. Distance 3. Three intervening words: Stove, ankle, parent, alcohol, coal, foot, child, whiskey, etc. Distance 7. Seven intervening words: Stove, ankle,
parent, alcohol, pasture, wish, bread, nest, coal, foot, child, whiskey, etc. Word pairs were assigned to and ordered within each list randomly. The ordering within each pair was also randomized so that the Kent-Rosanoff stimulus word preceded its associate in half the pairs and followed it in the others. The ordering ofthelist types was randomized independentlyfor each S. Each S thus had an independently randomized sequence of lists and sequence of words within lists. In addition to the experimental lists, there were four practice lists; two of four words each and two of 16 words each. The words in the practice lists were 40 nouns of Thorndike-Lorge AA frequency (Thorndike and Lorge, 1944). They were also assigned and ordered at random, independently for each S. Apparatus. The stimuli were shown with a slide projector. The exposure times and the intervals between words were controEed by a Gerbrands programmer modified to run at 15 rpm. Subjects. The Ss were 70 college students who were paid for participating. Procedure. Each S was run individually.He was first shown a four-word practice list, a 16-word practice list and then the four main lists at one rate. Then he was told that the rate would be changed and was given another sequence of two practice lists and four main lists at the other rate. Half of the Ss had the 1-sec interval lists first. Half had the 3-secintervallistsfirst. All words were exposed for 1 sec. The S said each word aloud when it appeared on the screen. After each 16-word list, S was given 90 sec to write his responses in a booklet.
Results The curves in Fig. 1 summarize the overall results. W i t h a n increase in i n t e r v e n i n g items between related words there is a drop in m e a n p r o p o r t i o n of recall from .771 to .671 per word in the 3-sec rate a n d from .730 to .592 on the 1-sec rate. Both curves decline m o n o t o n i c a l l y b u t the shapes of the two curves differ. Analysis of variance was carried out with order, i.e., fast rate first vs. slow rate first, as a between-S variable a n d n u m b e r of i n t e r v e n i n g items, rate a n d serial position as w i t h i n - S variables. The m a i n effect of order was n o t significant F < 1. The m a i n effects of n u m b e r o f intervening items, F(3, 2 0 4 ) = 3 5 . 3 2 ; rate,
DISTANCE IN FREE RECALL
.8O (~ .75 o
u
. 70
~
.65
0 a:
:60
3SEC
1 SEC ,,o I
I
I
0
1
2
I
I
3 4 DISTANCE
I
I
I
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6
7
FIG. 1. P r o p o r t i o n s o f associated w o r d s recalled at 1- a n d 3-sec p r e s e n t a t i o n rates as a f u n c t i o n of n u m b e r
of words between the pair members (distance). F(1, 68)= 67.03, and serial position, F(15, 1020)=34.54 were all highly significant, p < .001. The use of conservative tests (Greenhouse and Geisser, 1959) does not alter the significance levels of the findings. Only one of the interactions involving the main variables attains significance--the interaction of number of intervening items and rate, F(3, 204) = 2.64, p < .05. A conservative test of this effect, rising reduced degrees of freedom, does not leave this significant. Examination of the serial position curves for the individual experimental conditions reveals patterns similar to those found before. The double peaked serial position curves are found over all conditions. There is only- one interaction with serial position that is indicated by the data--the interaction of rate with serial position. The curves for the 3-sec rate and the 1-sec rate are clearly separate except that they merge in the last three positions. This agrees with earlier findings (Glanzer and Cunitz, 1966; Murdock, 1962). The interaction for serial position and rate was, however, not significant, F(15, 1020) = 1.65, .05 < p <.10. There is not even a suggestion of interaction between numbers of intervening items and serial position. Discussion
The effect of the number of intervening words fits the picture of a limited-capacity STS
107
discussed in preceding work. The data show that the probability of recall of mnemonically related words is a declining function of the number of words separating them. The interpretation of this function is that the probability that both members of a related pair will be in STS at the same time declines with the number of words separating the pair. As each intervening word enters, the probability increases that the first member of the pair will leave STS. If the first member of the pair has left STS, then the facilitative effect of the mnemonic relation between the words does not occur. The curves in Fig. 1 are then a function of the decline in probability of a word being in STS with each successive new word. The curves are, however, not a simple function of that decline in probability. They reflect a summation of probabilities over several successive inputs. The curves show, moreover, that the effects are not simply due to the passage of time. The effect of increasing inter-item interval is the opposite of that of increasing the number of items between pairs. It increases the total amount recalled. Thus, the STS is limited with respect to number of items it holds, not the amount of time it holds them. The lack of any marked difference between the serial position curves for the two rates and for the four interval conditions, permits averaging across all serial positions as in Fig. 1. The evidence for the lack of a difference is the nonsignificant Fs for the interaction of serial position with number of intervening items and with rate. The absence of interaction of number of intervening items with serial position is in line with data indicating the absence of interaction of presenc e vs. absence of mnemonic structure with serial position (Glanzer and Meinzer, 1967). The absence of an interaction indicates that the mnemonic structure has its effect while the words are in STS, making rehearsal in STS more efficient. An increase in efficiency of rehearsal also increases the probability that the words will be registered in LTS. Thus the effects of mnemonic structure would appear in both STS and LTS
108
GLANZER
and therefore across all serial positions. I f the m n e m o n i c structure affected only the probability o f registration in LTS, then the separation of the serial position curves should hold for all but the last few positions, the positions identified with output f r o m STS. The absence of a significant interaction between presentation rate and serial position seems to run contrary to previous findings (Gianzer and Cunitz, 1966; M u r d o c k , 1962). I n those studies, differences in rate affect all but the last few positions in the serial position curve. Examination o f the serial position curves indicates that the same effects are present in the present data. The interaction test is not specific and therefore, in this case, conservative. Analysis o f the difference between the 3- and 1-see means for the first four positions finds a highly significant F(1, 6 8 ) = 26.40, p < .001 ; for the last four positions, however, F(1, 68) = 1.81, p > .10. The merging o f the last few positions in the serial position curve occurs here as previously. The effect is, however, a small one in this experiment. EXPERIMENT I I : REPETITION, NUMBER OF INTERVENING ITEMS AND PRESENTATION RATE Repeating an item within a free recall list can, depending on the experimental conditions, lower recall (Glanzer and Meinzer, 1967), or raise recall (Waugh, 1962, 1963). The experiments cited above differed in a n u m b e r of ways so that it is not possible, on the basis o f those experiments, to specify a single variable to account for the differences. One variable, however, should be i m p o r t a n t - - t h e distance between repetitions o f a list word. W h e n words in a free-recall list are repeated, the repetition can occur while the first representation is still in STS or after it has left STS. I f the first representation has left STS, then it would be reasonable to view the S as being given two independent trials to learn that word. If, however, the second representation enters STS while the first is still there, several possibilities seem reasonable. T w o will be considered here: (a) The two representations are processed
independently as they are when they are in STS at different times; (b) the two representations are processed as a single representation. The first alternative implies that change in the distance between repetitions of a w o r d will have no effect. There are some data (Waugh, 1963) that support the first alternative. Other data indicate that distance does have an effect (Peterson, Wampler, Kirkpatrick, and Saltzman, 1963; Melton and Shulman, 1967). Some data (Glanzer and Cunitz, 1966) indicate that repeated presentation o f words in immediate succession gives no better performance than leaving empty a period o f time equal to that used for repetition, i.e., equivalent spacing. Three immediately successive repetitions gave no better recall than one presentation over the same time interval. These data would lend support to the second alternative. Method Parallel to Exp. I, both the number of words intervening between the repeated words and the presentation rate were varied. Each S was given 13 free recall
lists at either a fast rate, 1-see interval between words-or a slow rate, 3-see interval. Each list consisted of 16 words--12 different words, four of which were repeated once. The apparatus and general procedure were the same as in Exp. I. Materials. The words used for all lists were drawn from a set of 220 monosyllabic AA (Thorndike and Lorge, 1944) nouns. In each word list, there were four repeated words, in the following conditions: Distance 0, no intervening items; Distance 1, one intervening item; Distance 2; and Distance 5. The intervening items could be either nonrepeated words or words from repetition pairs. Repetition pairs were assigned at random to positions in the list with the following restrictions. Each repetition condition occurred no more than twice within a single list. Across the 13 lists, each repetition condition appeared once and only once at each possible serial position. Since each list consisted of 16 positions or items, there were 16 positions at which unrepeated items could appear, 15 at which zero-interval repetitions could appear, 14 at which one-interval repetitions could appear, etc. In addition to the 13 main lists there were two practice lists, of the same length and structure as the main lists. Twenty-five different sets of lists were generated by independent randomization. Within each randomization, three Ss were given the lists at the 1-see rate and three Ss were given the lists at a 3-see rate.
DISTANCE IN FREE RECALL
Subjects. The Ss were 150 introductory psychology students who participated in fulfillment of a course requirement. Procedure.The only major differencein the procedure from Exp. I was that S was shown lists at only one presentation rate, either 1 or 3 sec. Results The curves in Fig. 2 summarize the overall results. There is an increase in the probability of recall with repetition. The effect of repetition depends on the number of intervening words, increasing monotonically with that number.
109
or the second presentation of the word, or both. To estimate the proportion of correct recalls that S should have if he had two independent trials with the word, the following computation was carried out, using the mean proportion of recalls of unrepeated words at equivalent serial positions. Estimated p =Pi + Pi+d+X --Pi'P~+d+ l, where i is the same serial position as the first member of a pair and d the distance condition. For example, the mean proportions of recalls of unrepeated words at a 1-sec rate for posi-
.90 .85 .BO ................. o
.75 .70 .65 .60 .55 .50 I
i
I
I
I
I
i
N
0
1
2 DISTANCE
3
4
5
FIG. 2. Proportions of repeated words recalled at 1- and 3-sec presentation rates as a function of number of words between the repeated words (distance). Also shown on the solid lines are the proportions for unrepeated words (N). The estimated proportionsfor two independent trials are shown on the broken lines.
Analysis of variance was carried out with rate as a between-S variable and repetition condition as a within-S variable. The main effect of both variables was highly significant-rate, F(1, 148) = 43.51, p < .001, and repetition condition, F(4, 592) = 110.20, p < .001. The interaction between repetition condition and rate was not significant, F(4, 592) = 1.56, p > .10. T o evaluate fully the gains made by S with repeated presentation of a word, some additional information is necessary. The S may be viewed as recalling a repeated word on the basis of either the first presentation of the word,
tions 1, 2, and 3 across the lists are .69, .56, and .53. An estimated proportion for a repeated word at Distance 0, Serial Positions 1 and 2 would be .69 + .56 - .39 = .86. An estimated proportion for a repeated word at Distance 1, Serial Positions 1 and 3 would be .69 + .53 .37 = .85. The mean of the estimated values obtained in this fashion was taken across all serial positions. Those means are plotted on the broken line in Fig. 2. The estimated values stay constant for all conditions except Distance 5, which rises. Because of the shape of the serial position curve, high and lowp's are being combined for Distance 5, rather than similar
110
GLANZER
values as in Distance 0, 1, or 2. The effect of combining very different p's is to give a higher overall mean. As can be seen in the figure, the mean performance under each distance condition falls below that estimated for two independent tries at the word in all conditions except Distance 5. Tests of the deviations of the obtained values from the theoretical values find that all distances except Distance 5 differ significantly, p < .05, from the corresponding estimated values. Serial position curves for the nonrepeated words were plotted for the 1- and 3-sec rates. The curves display the effects found previously --separation at all but the last few positions. In these data the curves clearly merge from positions 12 through 16.
Discussion
respect to Exp. II, it could be argued that the effect of increasing distance of the repetitions is due to the placement of the two presentations in different contexts. Thus, a repetition at Distance 0 gives the repeated word only two neighboring items. A repetition at Distance 2 gives it four different neighboring items. If associations are formed with the neighboring items and those items function as retrieval cues, then an increase in recall would be expected. This approach would have to be developed further to explain the difference between Distance 2 and 5. If the development defines neighboring items as those three or four or five positions away, then a rationale for this definition would have to be constructed. The STS is the idea used here to rationalize these effects. The curves displayed in Figs. 1 and 2 are considered in this interpretation as traces of STS. REFERENCES
Again the effect of the number of intervening ATKINSON,R. C., AND Ssr~rmN, R. M. Mathematical models for memory and learning. In D. P. Kimble words fits the picture of a limited-capacity STS. (Ed.), The proceedings of the third conference on As the distance between the first and second learning, remembering and forgetting. New York: presentation of an item increases, so that it is New York Academy of Sciences, in press. less likely that the two representations of the COHEN, B. H. Recall of categorized word lists. J. exp. Psychol., 1963, 66, 227-234. item co-occur in STS, there is a closer approximation to the recall expected on the basis of DEES~, J. Influence of inter-item associative strength upon immediate free recall. Psychol. Rep., 1959, two independent trials. 5, 305-312. In preceding work (Glanzer and Cunitz, GLANZER,M., ANDCUNITZ, A. R. Two storage mech1966; Glanzer and Meinzer, 1967) the shape of anisms in free recall. J. verb. Learn. verb. Behav., 1966, 5, 351-360. the serial position curve was the dependent variable used to analyze characteristics of GLANZER,M., AND MEINZER,A. The effects of intralist activity on free'recall. J. verb. Learn. verb. Behav., STS. Here the serial position curve was not 1967, 6, 928-935. used in this way. With pairs of words under GREENHOUSE,S. W., AND GEISSER,S. On the methods study, the specification of the locus of an effect in the analysis of profile data. Psychometrika, 1959, 24, 95-112. in the serial order becomes less clear. The two major variables considered in Exps. I and II MAYZN~R, M. S., AND "I~.ESSELTI M. E. Incidental learning: A function of associative strength and do not, moreover, lend themselves to such distance between S-R pairs. J. Psychol., 1962, 53, analysis. Repetition distance, for example, does 155-160. not permit comparison of serial position curves MELTON,A. W., AND SHULMAN,H. G. Further studies of a distributed practice effect on probability of since the number of possible positions varies recall in free recall. Paper read at Psychonomic with distance. On a 16-item list there are 15 Society meeting, September, 1967. positions for pairs at Distance 0, and only 10 MURDOCK, B. B., JR. The serial position effect in free positions at Distance 5. recall. J. exp. Psychol., 1962, 64, 482-488. There are, of course, other ways of viewing MtmoocK, B. B., JR. Recent developments in shortterm memory. Brit. J. Psychol., 1967, 58, 421-433. the results obtained in Exps. I and II. With
DISTANCE IN FREE RECALL
PETERSON,L. R. Short-term verbal memory and learning. Psychol. Rev., 1966, 73, 193-207. PETERSON,L. R., WAMPLER,R., KIRKPATRICK,M., AND SALTZMAN,D. Effect of spacing presentations on retention of a paired associate over short intelvals. J. exp. Psychol., 1963, 66, 206-209. RUSSELL, W. A., AND JENKINS, J. J. The complete Minnesota norms for responses to 100 wordsfrom the Kent-Rosanoff Association Test.- ONR Tech. Rep. No. 11, 1954. TrIORNDIKE, E. L., AND LORGE, I. The teacher's word book of 30,000 words. New York: Bureau of
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Publications, Teacher's College, Columbia University, 1944. WAUCH, N. C. Immediate memory as a function of repetition. J. verb. Learn. verb. Behav., 1963, 2, 107-112. WAUGH,N. C. The effect of intralist repetition on free recall. J. verb. Learn. verb. Behav., 1962, 1, 95-99. WAUOH,N. C., AND NOR~tAN,D. A. Primary memory. Psychol. Rev., 1965, 72, 89-104. (Received May 31, 1968)