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A breakdown of the total-time law in free-recall learning
JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR
9, 573-580 (1970)
A Breakdown of the Total-Time Law in Free-Recall Learning BENTON J. UNDERWOOD1 Northwestern University, Evanston, Illinois 60201
Five experiments are reported in which single-trial free recall followed various frequencies of repetition under massed (MP) and distributed (DP) schedules. All experiments showed the DP schedule to result in far better recall than the MP schedule, and the difference between MP and DP increased as the frequency of repetition increased. This was true for sentences, nonsense syllables, and words. Various activities inserted between successive words in the lists did not change the basic findings.
The total-time law states that the amount learned is a direct function of study time regardless of how that time is distributed. The evidence brought together in support of this law by Cooper and Pantle (1967) is impressive and could be further documented by recent studies (e.g., Zacks, 1969). The present paper is concerned with exceptions to the law. These exceptions have grown rapidly in number and all seem to result from the same basic procedures. If a unit to be learned is presented more than once in a continuous series the schedule may be by massed practice (MP) or by distributed practice (DP). Under MP, the successive occurrences of an item occupy adjacent positions. Under DP, at least one other item falls between successive occurrences. Thus, for an item (X) presented three times, the MP schedule might be: F, G, B, X, X, X, P, M, etc. For DP, the schedule might be: F, X, G, B, X, P, X, M, etc. Recall
following the DP schedule is usually far greater than the recall following the MP schedule in spite of the fact that the total time the items are presented is equivalent. Exceptions to the time law resulting from these procedures appear to have considerable generality. They occur in the continuous paired-associate task (Calfee, 1968; Greeno, 1964; Landauer, 1969), in free-recall learning (Madigan, 1969; Melton, 1967; Underwood, 1969) and apparently in short-term memory procedures (e.g., Borkowski, 1967). There has been an occasional exception in free-recall learning (e.g., Waugh, 1967). The major purpose of this paper is to report studies which further extend the generality of the exception to the time law for free-recall learning. The first two experiments deal with the free recall of sentences. R o t h k o p f and Coke (1963; 1966) have shown that the recall of sentences presented twice will be better if the two occurrences are separated by other sentences than if not. Two experiments will be reported, one using mixed lists, the other unmixed lists, in both of which the frequency of presentation is extended beyond those frequencies employed by R o t h k o p f and Coke.
This paper originated from the author's participation in the symposium, "Distribution effects in learning and memory," Midwestern Psychological Association, May 9, 1969. The nature of this report, however, is quite different from the original presentation. A particular finding reported at that time was judged to be of considerable theoretical importance. The failure EXPERIMENT 1 to replicate the finding in subsequent studies has M e t h o d resulted in removal of much of the theoretical content. This work was supported by Project NR 154-057, Materials. Twenty-four different sentences comContract N00014-67-A-356-0010, between North- prised the learning task. The meaning of each sentence western University and the Office of Naval Research. was somewhat abstract as may be seen from the fol573
574
UNDERWOOD
lowing three illustrations: Universal law always follows a pattern, Those who talk too much do little else, Back o f all ideas is specialized knowledge. Mixed lists were constructed in which sentences occurred 1, 2, 3, 4, or 6 times. Half of the sentences were given by MP, half by DP. The latter schedule required only that at least one other sentence be inserted between successive occurrences of a given sentence. There were two sentences for each frequency level (2, 3, 4, 6) for MP and two for DP. Four sentences occurred once within the body of the list. Two buffer sentences were used at the beginning of the list, two at the end. Thus, there was a total of 68 positions in the series. Five different forms were used. Sentences for each fo?m were assigned randomly to conditions subject to the restriction that the same sentence not be used more than once for a given condition in different forms. Procedure and subjects. The sentences were recorded on tape at a 10 sec rate; the first 5 sec (on the average) were used to speak the sentence, the remaining 5 sec were blank. The Ss were run in groups, 18 on each form, for a total of 90 Ss. Instructions emphasized that S should try to remember the sentences verbatim if possible, but that if this were not possible the idea of the sentence should be remembered with recall being expressed in S's own words. Instructions also informed S that order of the sentences in recall was unimportant. After the last sentence was presented, prepared data sheets were passed out, and the basic instructions for written recall repeated. Recall attempts were halted when it appeared that the supply was exhausted, a period estimated at from 8-10 rain.
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Scoring. Sentences were scored on a three-point scale. A 3 was assigned if the recall was essentially verbatim (minor deviations were allowed if the meaning was not changed, e.g., changing a singular to plural). A 2 was assigned if the meaning was correct but the wording changed, e.g., A man who says much does little else instead of A man who talks too much does little else. A score of 1 was given if the basic idea was modified but recall clearly demonstrated some knowledge of the sentence, e.g., All life consists o f chance instead of Life is filled with an element o f chance. Very few sentences were given a score of 1. Mean points per sentence is used here as the response measure. The results were the same if only the number of sentences rated 3 was used.
Results There were clear primacy and recency effects, so the four buffer sentences were not included in the analysis. The mean points per sentence are plotted in Figure 1 as a function of frequency and schedule. Recall following the DP schedule is far superior to that following the MP schedule ( F = 219.92), and the interaction between schedule and frequency is also apparent ( F = 18.05). The five forms did not produce differences in overall recall but there were significant interactions between form and the other variables which, it is pre-
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FIG. I. Free recall of sentences as a function of frequency of presentation and type of schedule in mixed lists.
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BREAKDOWN IN TOTAL-TIME LAW
sumed, result f r o m differences in difficulty a m o n g the sentences. T w o other observations will be reported. In earlier studies with lists o f discrete words it was f o u n d t h a t when Ss were asked to m a k e frequency j u d g m e n t s ( n u m b e r o f different times each w o r d had occurred) the m e a n j u d g m e n t s paralleled the recall results ( U n d e r w o o d , 1969). It was as if there h a d been a reception b l o c k u n d e r the M P schedule. One a d d i t i o n a l g r o u p o f Ss was run in the present experim e n t ; these Ss were a s k e d to m a k e frequency j u d g m e n t s o f the sentences. F o r 21 Ss for one f o r m o f the list the m e a n j u d g m e n t s were 2.26, 2.52, 2.85, a n d 4.69 for frequencies o f 2, 3, 4, a n d 6 following the M P schedule. F o r D P the values were 3.04, 3.33, 5.61, a n d 6.92. Thus, in terms o f frequency i n f o r m a t i o n as well as in terms o f recall, the sentences a p p r o x i m a t e the results f o u n d in discrete words, In some studies with discrete words, serialp o s i t i o n effects extending well into the b o d y o f the list have been found. Excluding the s h a r p p r i m a c y a n d recency effects, items tow a r d the end o f the list were better recalled t h a n those t o w a r d the beginning. A n examin a t i o n o f the position-recall relationship for
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the present d a t a showed these same p o s i t i o n effects. Since, on the average, the last occurrence o f a D P sentence occurred later t h a n the last occurrence o f a c o r r e s p o n d i n g M P sentence, some o f the M P - D P effect o f F i g u r e 1 must be a t t r i b u t e d to position differences. While this can only be a small p o r t i o n o f the total difference, a second experiment was carried out to eliminate this factor entirely. EXPERIMENT 2
Method The sentences were the same as used in Experiment 1. There were 10 different unmixed lists representing five forms with a DP and an MP list for each form. Sixteen different sentences occurred only once with five of these being buffers (three at the beginning, two at the end). Two sentences were used at each frequency level of 2, 3, 4, and 5 frequencies. For a given form, the MP and DP lists were parallel in that a given sentence served exactly the same function in both lists. The last occurrence of a given sentence used at a given frequency level in both lists held the same serial position in both lists. Position differences, therefore, cannot influence the findings. A total of 100 Ss was run in groups of 10; 50 on the five MP forms and 50 on the five DP forms, 10 Ss per form. The MP and DP forms were alternated for successive groups of Ss. All other procedures were the same as in Experiment 1. I
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FIG. 2. Free recall of sentences as a function of frequency of presentation and type of schedule in unmixed lists.
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UNDERWOOD
Results
a n d it is possible that the effect w o u l d occur with higher frequencies. In the present study, children between the ages o f 9 a n d 14 were used, s o m e w h a t y o u n g e r on the average than those used by Landauer. 2
The results are p l o t t e d in Figure 2. The superiority o f the D P lists over the M P lists is again a p p a r e n t ( F = 34.43), a n d the M P - D P by frequency interaction is significant, F(3, 270)=7.16, p<.01. These statistics were calculated on the results for frequencies o f two a n d higher. P r i m a c y effects were a p p a r e n t only for the first position, recency effects only for the last position. Between positions 2-43 there was a flat recall curve for sentences presented once. Thus, unlike the results for Experiment 1, positions effects were n o t present. The results o f Experiments 1 a n d 2 fully confirm the previous findings o f R o t h k o p f a n d C o k e (1963; 1966) and show in a d d i t i o n t h a t the M P - D P effect increases as frequency o f p r e s e n t a t i o n increases.
Method The lists were composed of 42 two-syllable nouns falling between 20 and 50 in the frequency values given by Thorndike and Lorge (1944). The words were exactly the same as those of a so-called List 2 in Experiments V and VI of an earlier report (Underwood, 1969). Five words were used to absorb primacy effects, five to absorb recency effects. Of the remaining 32, eight were presented once within the body of the list. Twelve words were presented under the MP schedule with four words at each of three frequency levels, 2, 3, and 4. The remaining 12 words served exactly the same functions under a DP schedule. There were three different lists differing only in words assigned to the various conditions. The lists contained 90 positions. The words were presented for a single trial by magnetic tape at a 5-sec rate. Each word was pronounced twice during the 5-sec interval. Immediately after the presentation of the last word, the Ss wrote as many
EXPERIMENT 3 L a n d a u e r (1967) has r e p o r t e d that Ss o f j u n i o r high school age do n o t show the M P - D P effect for c o m m o n words. However, m a x i m u m frequency o f occurrence was two, I
2 This experiment was conducted by Mary Jean Bach. I
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Fro. 3. Free recall of discrete words by children (ages 9-14 years) as a function of frequency and schedule.
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BREAKDOWN IN TOTAL-TIME L A W
words as they could remember. There were 30 children run in groups of 10 each, with 10 being assigned to each of the three lists.
Results Percent recall as a function of the two variables is shown in Figure 3. The results are quite c o m p a r a b l e to those f o u n d with college students using the same list, although overall recall is less. U n d e r the M P schedule there is little increase in recall with increasing frequency, whereas u n d e r D P there is a sharp relationship. Statistical analysis, based only on frequencies 2, 3, a n d 4, confirm the apparent differences. F o r M P - D P , F = 45.00; for frequency, F(2, 134) = 5.11, p < .01; a n d for the interaction, F(2, 134) = 3.62, p < . 0 5 . Unlike L a n d a u e r ' s findings, the present results show a m a r k e d difference between M P a n d D P schedules in free-recall learning of children. EXPERIMENT 4 The materials used in this experiment were nonsense syllables, with the variable of major interest being rate of presentation. If it is assumed that it takes longer to establish a
stable code or representational response for a nonsense syllable t h a n for a word, an M P schedule might be less deleterious for syllables when they are presented at a rapid rate t h a n when presented at a slow rate. A n additional immediate presentation at a rapid rate might allow S to establish a stable code that would n o t be established on the initial presentation. A t a slow rate, the initial presentation would be sufficient.
Method Material. The nonsense syllables varied between 4 6 ~ and 69~ association value (Noble, 1961). The 24 critical syllables were sorted into four subgroups of six each so that the mean association values of the subgroups were equivalent (57 ~). The six syllables in one subgroup cccurred once in a list, and the six items in the remaining three groups occurred either 2, 3, or 4 times. Four additional syllables were used in positions 1-4, and two in the two terminal positions. The list of 30 syllables had minimal formal similarity. Five vowels were each used six times, and no consonant was used more than twice as the initial letter nor more than twice as the terminal letter. Two unmixed lists were constructed. In one list all syllables occurring more than once were given an MP schedule, and the corresponding items in the other list a DP schedule. The position of the last occurrence of a given item was m
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Fro. 4. Free recall of nonsense syllables as a function of frequency, presentation rate, and type of schedule.
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UNDERWOOD
exactly the same in both lists for syllables occurring more than once. Procedure and subjects. There were four groups of 20 Ss each, differentiated by the rate of presentation of the syllables (2 or 5 sec) and by the type of list (MP or DP). The syllables were presented on slides with a special timer governing the projection rate. It should be clear that all items within a given list were all presented at the same rate. After a single presentation of the list, written recall was taken on prepared sheets. Results The results are shown in Figure 4. Again, there is the usual large M P - D P difference ( F = 17.01), a frequency effect ( F = 19.01), a n d an interaction between the two variables, F(3, 2 2 8 ) = 2.99, p < .05. The rate variable was n o t significant, F(1, 76) = 3.26, p > .05, a n d none o f the interactions involving rate even a p p r o a c h e d significance. It is to be n o t e d t h a t the two M P groups do n o t differ; 5 sec versus 2 sec per item does not p r o d u c e a difference regardless o f frequency. This is p a r t i c u l a r l y puzzling for syllables occurring once. These two groups did differ in the recall o f filler syllables ( 2 2 ~ vs 4 3 ~ ) . F u r t h e r , there is no a p p a r e n t reason why D P a n d M P schedules should influence syllables presented once at the 5-sec rate. It seems likely, therefore, t h a t the recall o f syllables presented once in the M P list at a 5-sec rate is, for some unk n o w n reason, u n d e r e s t i m a t e d by p e r h a p s
8-1O7oo. The d a t a give no substantial s u p p o r t to the hypothesis t h a t the difference between M P a n d D P should be less the m o r e r a p i d the rate o f p r e s e n t a t i o n for units o f relatively low meaningfulness. T h e differences are in the a p p r o p r i a t e direction b u t far f r o m significant statistically. The results, therefore, merely confirm previous findings (e.g., L a n d a u e r , 1967) showing the M P - D P effect with syllables. EXPERIMENT 5 I n a previous study it was shown t h a t the lag between successive presentations o f a w o r d in a free-recall t a s k was n o t related to recall
( U n d e r w o o d , 1969). One w o r d falling between successive presentations resulted in recall t h a t was j u s t as high as when 20 words s e p a r a t e d the two occurrences. A l t h o u g h this finding is at odds with the results o f other investigators (e.g., M a d i g a n , 1969; Melton, 1967), it is responsible for the experiment to be r e p o r t e d now. The lack o f a lag effect suggested that if S could be led to process some neutral m a t e r i a l between the successive occurrences o f an M P item, this item might be recalled at the level o f a D P item. F u r t h e r , the l i k e l i h o o d o f this occurring should be greater the greater the d e m a n d s the processing o f the neutral m a t e r i a l m a d e u p o n m e m o r y . This follows f r o m a crude analogy with the case in which a w o r d to be m e m o r i z e d falls between successive occurrences o f the item (DP). In any event, this experiment a t t e m p t e d to manipulate the nature o f the processing o f neutral m a t e r i a l inserted after each word. Method The mixed list was exactly the same as that used in Experiment 3 of this report. The list was shown by a memory drum, and each successive word appeared for 4 sec. After each 4-sec presentation of a word a l-sec interval occurred and the major variable was the task required of the S during this 1-sec period. In one condition, the Blank condition, a blank portion of the tape appeared for 1 sec and S was required to do nothing. In a second condition, the Read condition, two single-digit numbers appeared separated by a plus sign (e.g., 3 + 4). The S was instructed merely to read (e.g., "three plus four") and was instructed not to add the two numbers. This task was assumed to require a minimal amount of memory processing. In a third condition, the Add condition, the same sets of numbers occurred as in the Read condition and the S was instructed to give the sum of the two numbers within the 1-sec period. Since there were 90 positions in the list, and since a pair of numbers occurred after each position, there were 90 sets of numbers, each one different from all others. It should be clear that a set of numbers (or a blank) separated all successive occurrences of an MP item. A total of 27 Ss was assigned to each of the three conditions by block randomization. The instructions were the usual ones for free-recall learning with the necessary additions to implement the handling of the numbers.
579
BREAKDOWN IN TOTAL-TIME LAW I
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FIG. 5. Free recall of discrete words as a function of frequency, type of schedule, and type of activity inserted between successive words (blank, add numbers, read numbers).
Results It might be anticipated that the different activities would produce differences in overall recall. As is apparent in Figure 5, they did. More particularly, when S was required to add the numbers, performance was depressed; merely reading the numbers had no effect when compared with the blank condition. Thus, it appears that the activities required did produce different demands on the S. Although Figure 5 suggests that the difference between MP and DP is attenuated when the S was required to add the figures, there is no statistical support for this. The critical statistic would be the M P - D P by Activity interaction and this gives an F of only 1.27 (when calculated using frequencies 2, 3, and 4). To explore further the influence of betweenword activities, an additional experiment was conducted in which the interval between words
was increased to 2 sec. One group of 50 Ss read the numbers, another group of 50 Ss added the numbers just as in Experiment 5. Increasing the between-word interval to 2 sec almost entirely removed the negative effect on overall recall produced by adding, but again the interaction between M P - D P and type of activity fell far short of significance ( F < I). It must be concluded that these manipulations have not influenced the basic relationship between recall and the M P - D P schedules.
DISCUSSION
The results of the five studies reported here extend the range of materials and conditions under which exceptions to the total-time law are found in free-recall learning. Unfortunately, the very consistency of the results across conditions and materials makes theory
580
UNDERWOOD
s p i n n i n g difficult. F o r theoretical purposes it would have been m u c h more useful to have discovered a situation in which the M P - D P difference was eliminated or at least markedly reduced in magnitude. F u r t h e r m o r e , such consistencies can make an investigator u n easy for it m a y m e a n that he is dealing with something that i n this situation is psychologically trivial. F o r example, if learning is depressed u n d e r M P because of i n a t t e n t i o n by S, it would be trivial; learning c a n n o t take place without input. REFERENCES
BORKOWSKI,J. G. Distributed practice in short-term memory. Journal of Verbal Learning and Verbal Behavior, 1967, 6, 66-72. CALFEE, R. C. lnterpresentation effects in pairedassociate learning. Journal of Verbal Learning and Verbal Behavior, 1968, 7, 1030-1036. COOPER, E. H., & PANTLE,A. J. The total-time hypothesis in verbal learning. Psychological Bulletin, 1967, 68, 221-234. GREENO, J. G. Paired-associate learning with massed and distributed presentation of items. Journal of Experimental Psychology, 1964, 67, 286-295. LANDAUER, T. K. Interval between item repetitions and free recall memory. Psychonomic Science, 1967, 8, 439-440. LANDAUER, T. K. Reinforcement as consolidation. Psychological Review, 1969, 76, 82-96.
MADIGAN,S. A. lntraserial repetition and coding processes in free recall. Journal of Verbal Learning and Verbal Behavior, 1969, 8, 828-835. MELTON,A. W. Repetition and retrieval from memory. Science, 1967, 158, 532. NOBLE,C. E. Measurements of association value (a), rated associations (a'), and scaled meaningfulness (m') for the 2100 CVC combinations of the English alphabet. Psychological Reports Monograph Supplement, 1961, 8, 487-521. ROTHKOPF, E. Z., & COKE,E. U. Repetition interval and rehearsal method in learning equivalences from written sentences. Journal of Verbal Learning and Verbal Behavior, 1963, 2, 406-416. ROTHKOPF, E. Z., t~. COKE, E. U. The effect of some variations in procedure on response repetition following verbal outcomes. Journal of Verbal Learning and Verbal Behavior, 1966, 5, 86-91. THORND1KE,E. L., & LORGE,I. The teacher's wordbook of 30,000 words. New York, Columbia University Press, 1944. UNDERWOOD, B. J. Some correlates of item repetition in free-recall learning. Journal of Verbal Learning and Verbal Behavior, 1969, 8, 83-94. WAUGH, N. C. Presentation time and free recall. Journal of Experimental Psychology, 1967, 73, 39-44. ZACKS, R. T. lnvariance of total learning time under different conditions of practice. Journal of Experimental Psychology, 1969, 82, 441-447.
(Received February 27, 1970)
9, 573-580 (1970)
A Breakdown of the Total-Time Law in Free-Recall Learning BENTON J. UNDERWOOD1 Northwestern University, Evanston, Illinois 60201
Five experiments are reported in which single-trial free recall followed various frequencies of repetition under massed (MP) and distributed (DP) schedules. All experiments showed the DP schedule to result in far better recall than the MP schedule, and the difference between MP and DP increased as the frequency of repetition increased. This was true for sentences, nonsense syllables, and words. Various activities inserted between successive words in the lists did not change the basic findings.
The total-time law states that the amount learned is a direct function of study time regardless of how that time is distributed. The evidence brought together in support of this law by Cooper and Pantle (1967) is impressive and could be further documented by recent studies (e.g., Zacks, 1969). The present paper is concerned with exceptions to the law. These exceptions have grown rapidly in number and all seem to result from the same basic procedures. If a unit to be learned is presented more than once in a continuous series the schedule may be by massed practice (MP) or by distributed practice (DP). Under MP, the successive occurrences of an item occupy adjacent positions. Under DP, at least one other item falls between successive occurrences. Thus, for an item (X) presented three times, the MP schedule might be: F, G, B, X, X, X, P, M, etc. For DP, the schedule might be: F, X, G, B, X, P, X, M, etc. Recall
following the DP schedule is usually far greater than the recall following the MP schedule in spite of the fact that the total time the items are presented is equivalent. Exceptions to the time law resulting from these procedures appear to have considerable generality. They occur in the continuous paired-associate task (Calfee, 1968; Greeno, 1964; Landauer, 1969), in free-recall learning (Madigan, 1969; Melton, 1967; Underwood, 1969) and apparently in short-term memory procedures (e.g., Borkowski, 1967). There has been an occasional exception in free-recall learning (e.g., Waugh, 1967). The major purpose of this paper is to report studies which further extend the generality of the exception to the time law for free-recall learning. The first two experiments deal with the free recall of sentences. R o t h k o p f and Coke (1963; 1966) have shown that the recall of sentences presented twice will be better if the two occurrences are separated by other sentences than if not. Two experiments will be reported, one using mixed lists, the other unmixed lists, in both of which the frequency of presentation is extended beyond those frequencies employed by R o t h k o p f and Coke.
This paper originated from the author's participation in the symposium, "Distribution effects in learning and memory," Midwestern Psychological Association, May 9, 1969. The nature of this report, however, is quite different from the original presentation. A particular finding reported at that time was judged to be of considerable theoretical importance. The failure EXPERIMENT 1 to replicate the finding in subsequent studies has M e t h o d resulted in removal of much of the theoretical content. This work was supported by Project NR 154-057, Materials. Twenty-four different sentences comContract N00014-67-A-356-0010, between North- prised the learning task. The meaning of each sentence western University and the Office of Naval Research. was somewhat abstract as may be seen from the fol573
574
UNDERWOOD
lowing three illustrations: Universal law always follows a pattern, Those who talk too much do little else, Back o f all ideas is specialized knowledge. Mixed lists were constructed in which sentences occurred 1, 2, 3, 4, or 6 times. Half of the sentences were given by MP, half by DP. The latter schedule required only that at least one other sentence be inserted between successive occurrences of a given sentence. There were two sentences for each frequency level (2, 3, 4, 6) for MP and two for DP. Four sentences occurred once within the body of the list. Two buffer sentences were used at the beginning of the list, two at the end. Thus, there was a total of 68 positions in the series. Five different forms were used. Sentences for each fo?m were assigned randomly to conditions subject to the restriction that the same sentence not be used more than once for a given condition in different forms. Procedure and subjects. The sentences were recorded on tape at a 10 sec rate; the first 5 sec (on the average) were used to speak the sentence, the remaining 5 sec were blank. The Ss were run in groups, 18 on each form, for a total of 90 Ss. Instructions emphasized that S should try to remember the sentences verbatim if possible, but that if this were not possible the idea of the sentence should be remembered with recall being expressed in S's own words. Instructions also informed S that order of the sentences in recall was unimportant. After the last sentence was presented, prepared data sheets were passed out, and the basic instructions for written recall repeated. Recall attempts were halted when it appeared that the supply was exhausted, a period estimated at from 8-10 rain.
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Scoring. Sentences were scored on a three-point scale. A 3 was assigned if the recall was essentially verbatim (minor deviations were allowed if the meaning was not changed, e.g., changing a singular to plural). A 2 was assigned if the meaning was correct but the wording changed, e.g., A man who says much does little else instead of A man who talks too much does little else. A score of 1 was given if the basic idea was modified but recall clearly demonstrated some knowledge of the sentence, e.g., All life consists o f chance instead of Life is filled with an element o f chance. Very few sentences were given a score of 1. Mean points per sentence is used here as the response measure. The results were the same if only the number of sentences rated 3 was used.
Results There were clear primacy and recency effects, so the four buffer sentences were not included in the analysis. The mean points per sentence are plotted in Figure 1 as a function of frequency and schedule. Recall following the DP schedule is far superior to that following the MP schedule ( F = 219.92), and the interaction between schedule and frequency is also apparent ( F = 18.05). The five forms did not produce differences in overall recall but there were significant interactions between form and the other variables which, it is pre-
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2
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Froquency
FIG. I. Free recall of sentences as a function of frequency of presentation and type of schedule in mixed lists.
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BREAKDOWN IN TOTAL-TIME LAW
sumed, result f r o m differences in difficulty a m o n g the sentences. T w o other observations will be reported. In earlier studies with lists o f discrete words it was f o u n d t h a t when Ss were asked to m a k e frequency j u d g m e n t s ( n u m b e r o f different times each w o r d had occurred) the m e a n j u d g m e n t s paralleled the recall results ( U n d e r w o o d , 1969). It was as if there h a d been a reception b l o c k u n d e r the M P schedule. One a d d i t i o n a l g r o u p o f Ss was run in the present experim e n t ; these Ss were a s k e d to m a k e frequency j u d g m e n t s o f the sentences. F o r 21 Ss for one f o r m o f the list the m e a n j u d g m e n t s were 2.26, 2.52, 2.85, a n d 4.69 for frequencies o f 2, 3, 4, a n d 6 following the M P schedule. F o r D P the values were 3.04, 3.33, 5.61, a n d 6.92. Thus, in terms o f frequency i n f o r m a t i o n as well as in terms o f recall, the sentences a p p r o x i m a t e the results f o u n d in discrete words, In some studies with discrete words, serialp o s i t i o n effects extending well into the b o d y o f the list have been found. Excluding the s h a r p p r i m a c y a n d recency effects, items tow a r d the end o f the list were better recalled t h a n those t o w a r d the beginning. A n examin a t i o n o f the position-recall relationship for
I
I
the present d a t a showed these same p o s i t i o n effects. Since, on the average, the last occurrence o f a D P sentence occurred later t h a n the last occurrence o f a c o r r e s p o n d i n g M P sentence, some o f the M P - D P effect o f F i g u r e 1 must be a t t r i b u t e d to position differences. While this can only be a small p o r t i o n o f the total difference, a second experiment was carried out to eliminate this factor entirely. EXPERIMENT 2
Method The sentences were the same as used in Experiment 1. There were 10 different unmixed lists representing five forms with a DP and an MP list for each form. Sixteen different sentences occurred only once with five of these being buffers (three at the beginning, two at the end). Two sentences were used at each frequency level of 2, 3, 4, and 5 frequencies. For a given form, the MP and DP lists were parallel in that a given sentence served exactly the same function in both lists. The last occurrence of a given sentence used at a given frequency level in both lists held the same serial position in both lists. Position differences, therefore, cannot influence the findings. A total of 100 Ss was run in groups of 10; 50 on the five MP forms and 50 on the five DP forms, 10 Ss per form. The MP and DP forms were alternated for successive groups of Ss. All other procedures were the same as in Experiment 1. I
I
~ DP
1.80 1.60
c 1.40 o 1.20
/
1.00
u~ c .80 o o. c .60 o
f+
.40 .20
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1
2
3
4
5
Frequency
FIG. 2. Free recall of sentences as a function of frequency of presentation and type of schedule in unmixed lists.
576
UNDERWOOD
Results
a n d it is possible that the effect w o u l d occur with higher frequencies. In the present study, children between the ages o f 9 a n d 14 were used, s o m e w h a t y o u n g e r on the average than those used by Landauer. 2
The results are p l o t t e d in Figure 2. The superiority o f the D P lists over the M P lists is again a p p a r e n t ( F = 34.43), a n d the M P - D P by frequency interaction is significant, F(3, 270)=7.16, p<.01. These statistics were calculated on the results for frequencies o f two a n d higher. P r i m a c y effects were a p p a r e n t only for the first position, recency effects only for the last position. Between positions 2-43 there was a flat recall curve for sentences presented once. Thus, unlike the results for Experiment 1, positions effects were n o t present. The results o f Experiments 1 a n d 2 fully confirm the previous findings o f R o t h k o p f a n d C o k e (1963; 1966) and show in a d d i t i o n t h a t the M P - D P effect increases as frequency o f p r e s e n t a t i o n increases.
Method The lists were composed of 42 two-syllable nouns falling between 20 and 50 in the frequency values given by Thorndike and Lorge (1944). The words were exactly the same as those of a so-called List 2 in Experiments V and VI of an earlier report (Underwood, 1969). Five words were used to absorb primacy effects, five to absorb recency effects. Of the remaining 32, eight were presented once within the body of the list. Twelve words were presented under the MP schedule with four words at each of three frequency levels, 2, 3, and 4. The remaining 12 words served exactly the same functions under a DP schedule. There were three different lists differing only in words assigned to the various conditions. The lists contained 90 positions. The words were presented for a single trial by magnetic tape at a 5-sec rate. Each word was pronounced twice during the 5-sec interval. Immediately after the presentation of the last word, the Ss wrote as many
EXPERIMENT 3 L a n d a u e r (1967) has r e p o r t e d that Ss o f j u n i o r high school age do n o t show the M P - D P effect for c o m m o n words. However, m a x i m u m frequency o f occurrence was two, I
2 This experiment was conducted by Mary Jean Bach. I
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2
3
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Fro. 3. Free recall of discrete words by children (ages 9-14 years) as a function of frequency and schedule.
577
BREAKDOWN IN TOTAL-TIME L A W
words as they could remember. There were 30 children run in groups of 10 each, with 10 being assigned to each of the three lists.
Results Percent recall as a function of the two variables is shown in Figure 3. The results are quite c o m p a r a b l e to those f o u n d with college students using the same list, although overall recall is less. U n d e r the M P schedule there is little increase in recall with increasing frequency, whereas u n d e r D P there is a sharp relationship. Statistical analysis, based only on frequencies 2, 3, a n d 4, confirm the apparent differences. F o r M P - D P , F = 45.00; for frequency, F(2, 134) = 5.11, p < .01; a n d for the interaction, F(2, 134) = 3.62, p < . 0 5 . Unlike L a n d a u e r ' s findings, the present results show a m a r k e d difference between M P a n d D P schedules in free-recall learning of children. EXPERIMENT 4 The materials used in this experiment were nonsense syllables, with the variable of major interest being rate of presentation. If it is assumed that it takes longer to establish a
stable code or representational response for a nonsense syllable t h a n for a word, an M P schedule might be less deleterious for syllables when they are presented at a rapid rate t h a n when presented at a slow rate. A n additional immediate presentation at a rapid rate might allow S to establish a stable code that would n o t be established on the initial presentation. A t a slow rate, the initial presentation would be sufficient.
Method Material. The nonsense syllables varied between 4 6 ~ and 69~ association value (Noble, 1961). The 24 critical syllables were sorted into four subgroups of six each so that the mean association values of the subgroups were equivalent (57 ~). The six syllables in one subgroup cccurred once in a list, and the six items in the remaining three groups occurred either 2, 3, or 4 times. Four additional syllables were used in positions 1-4, and two in the two terminal positions. The list of 30 syllables had minimal formal similarity. Five vowels were each used six times, and no consonant was used more than twice as the initial letter nor more than twice as the terminal letter. Two unmixed lists were constructed. In one list all syllables occurring more than once were given an MP schedule, and the corresponding items in the other list a DP schedule. The position of the last occurrence of a given item was m
50 /
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Frequency
Fro. 4. Free recall of nonsense syllables as a function of frequency, presentation rate, and type of schedule.
578
UNDERWOOD
exactly the same in both lists for syllables occurring more than once. Procedure and subjects. There were four groups of 20 Ss each, differentiated by the rate of presentation of the syllables (2 or 5 sec) and by the type of list (MP or DP). The syllables were presented on slides with a special timer governing the projection rate. It should be clear that all items within a given list were all presented at the same rate. After a single presentation of the list, written recall was taken on prepared sheets. Results The results are shown in Figure 4. Again, there is the usual large M P - D P difference ( F = 17.01), a frequency effect ( F = 19.01), a n d an interaction between the two variables, F(3, 2 2 8 ) = 2.99, p < .05. The rate variable was n o t significant, F(1, 76) = 3.26, p > .05, a n d none o f the interactions involving rate even a p p r o a c h e d significance. It is to be n o t e d t h a t the two M P groups do n o t differ; 5 sec versus 2 sec per item does not p r o d u c e a difference regardless o f frequency. This is p a r t i c u l a r l y puzzling for syllables occurring once. These two groups did differ in the recall o f filler syllables ( 2 2 ~ vs 4 3 ~ ) . F u r t h e r , there is no a p p a r e n t reason why D P a n d M P schedules should influence syllables presented once at the 5-sec rate. It seems likely, therefore, t h a t the recall o f syllables presented once in the M P list at a 5-sec rate is, for some unk n o w n reason, u n d e r e s t i m a t e d by p e r h a p s
8-1O7oo. The d a t a give no substantial s u p p o r t to the hypothesis t h a t the difference between M P a n d D P should be less the m o r e r a p i d the rate o f p r e s e n t a t i o n for units o f relatively low meaningfulness. T h e differences are in the a p p r o p r i a t e direction b u t far f r o m significant statistically. The results, therefore, merely confirm previous findings (e.g., L a n d a u e r , 1967) showing the M P - D P effect with syllables. EXPERIMENT 5 I n a previous study it was shown t h a t the lag between successive presentations o f a w o r d in a free-recall t a s k was n o t related to recall
( U n d e r w o o d , 1969). One w o r d falling between successive presentations resulted in recall t h a t was j u s t as high as when 20 words s e p a r a t e d the two occurrences. A l t h o u g h this finding is at odds with the results o f other investigators (e.g., M a d i g a n , 1969; Melton, 1967), it is responsible for the experiment to be r e p o r t e d now. The lack o f a lag effect suggested that if S could be led to process some neutral m a t e r i a l between the successive occurrences o f an M P item, this item might be recalled at the level o f a D P item. F u r t h e r , the l i k e l i h o o d o f this occurring should be greater the greater the d e m a n d s the processing o f the neutral m a t e r i a l m a d e u p o n m e m o r y . This follows f r o m a crude analogy with the case in which a w o r d to be m e m o r i z e d falls between successive occurrences o f the item (DP). In any event, this experiment a t t e m p t e d to manipulate the nature o f the processing o f neutral m a t e r i a l inserted after each word. Method The mixed list was exactly the same as that used in Experiment 3 of this report. The list was shown by a memory drum, and each successive word appeared for 4 sec. After each 4-sec presentation of a word a l-sec interval occurred and the major variable was the task required of the S during this 1-sec period. In one condition, the Blank condition, a blank portion of the tape appeared for 1 sec and S was required to do nothing. In a second condition, the Read condition, two single-digit numbers appeared separated by a plus sign (e.g., 3 + 4). The S was instructed merely to read (e.g., "three plus four") and was instructed not to add the two numbers. This task was assumed to require a minimal amount of memory processing. In a third condition, the Add condition, the same sets of numbers occurred as in the Read condition and the S was instructed to give the sum of the two numbers within the 1-sec period. Since there were 90 positions in the list, and since a pair of numbers occurred after each position, there were 90 sets of numbers, each one different from all others. It should be clear that a set of numbers (or a blank) separated all successive occurrences of an MP item. A total of 27 Ss was assigned to each of the three conditions by block randomization. The instructions were the usual ones for free-recall learning with the necessary additions to implement the handling of the numbers.
579
BREAKDOWN IN TOTAL-TIME LAW I
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2
3
4
Frequency
FIG. 5. Free recall of discrete words as a function of frequency, type of schedule, and type of activity inserted between successive words (blank, add numbers, read numbers).
Results It might be anticipated that the different activities would produce differences in overall recall. As is apparent in Figure 5, they did. More particularly, when S was required to add the numbers, performance was depressed; merely reading the numbers had no effect when compared with the blank condition. Thus, it appears that the activities required did produce different demands on the S. Although Figure 5 suggests that the difference between MP and DP is attenuated when the S was required to add the figures, there is no statistical support for this. The critical statistic would be the M P - D P by Activity interaction and this gives an F of only 1.27 (when calculated using frequencies 2, 3, and 4). To explore further the influence of betweenword activities, an additional experiment was conducted in which the interval between words
was increased to 2 sec. One group of 50 Ss read the numbers, another group of 50 Ss added the numbers just as in Experiment 5. Increasing the between-word interval to 2 sec almost entirely removed the negative effect on overall recall produced by adding, but again the interaction between M P - D P and type of activity fell far short of significance ( F < I). It must be concluded that these manipulations have not influenced the basic relationship between recall and the M P - D P schedules.
DISCUSSION
The results of the five studies reported here extend the range of materials and conditions under which exceptions to the total-time law are found in free-recall learning. Unfortunately, the very consistency of the results across conditions and materials makes theory
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UNDERWOOD
s p i n n i n g difficult. F o r theoretical purposes it would have been m u c h more useful to have discovered a situation in which the M P - D P difference was eliminated or at least markedly reduced in magnitude. F u r t h e r m o r e , such consistencies can make an investigator u n easy for it m a y m e a n that he is dealing with something that i n this situation is psychologically trivial. F o r example, if learning is depressed u n d e r M P because of i n a t t e n t i o n by S, it would be trivial; learning c a n n o t take place without input. REFERENCES
BORKOWSKI,J. G. Distributed practice in short-term memory. Journal of Verbal Learning and Verbal Behavior, 1967, 6, 66-72. CALFEE, R. C. lnterpresentation effects in pairedassociate learning. Journal of Verbal Learning and Verbal Behavior, 1968, 7, 1030-1036. COOPER, E. H., & PANTLE,A. J. The total-time hypothesis in verbal learning. Psychological Bulletin, 1967, 68, 221-234. GREENO, J. G. Paired-associate learning with massed and distributed presentation of items. Journal of Experimental Psychology, 1964, 67, 286-295. LANDAUER, T. K. Interval between item repetitions and free recall memory. Psychonomic Science, 1967, 8, 439-440. LANDAUER, T. K. Reinforcement as consolidation. Psychological Review, 1969, 76, 82-96.
MADIGAN,S. A. lntraserial repetition and coding processes in free recall. Journal of Verbal Learning and Verbal Behavior, 1969, 8, 828-835. MELTON,A. W. Repetition and retrieval from memory. Science, 1967, 158, 532. NOBLE,C. E. Measurements of association value (a), rated associations (a'), and scaled meaningfulness (m') for the 2100 CVC combinations of the English alphabet. Psychological Reports Monograph Supplement, 1961, 8, 487-521. ROTHKOPF, E. Z., & COKE,E. U. Repetition interval and rehearsal method in learning equivalences from written sentences. Journal of Verbal Learning and Verbal Behavior, 1963, 2, 406-416. ROTHKOPF, E. Z., t~. COKE, E. U. The effect of some variations in procedure on response repetition following verbal outcomes. Journal of Verbal Learning and Verbal Behavior, 1966, 5, 86-91. THORND1KE,E. L., & LORGE,I. The teacher's wordbook of 30,000 words. New York, Columbia University Press, 1944. UNDERWOOD, B. J. Some correlates of item repetition in free-recall learning. Journal of Verbal Learning and Verbal Behavior, 1969, 8, 83-94. WAUGH, N. C. Presentation time and free recall. Journal of Experimental Psychology, 1967, 73, 39-44. ZACKS, R. T. lnvariance of total learning time under different conditions of practice. Journal of Experimental Psychology, 1969, 82, 441-447.
(Received February 27, 1970)