Information processing strategies used in the encoding of linear orderings

JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR 11,727-740 (1972)

Information Processing Strategies Used in the Encoding of Linear Orderings 1 GEORGE R. POTTS 2

Indiana University, Bloomington, Indiana 47401

Two linear orderings of the form A > B > C > D were incorporated into a meaningful paragraph by describing the pairwise relations between the four terms. Subjects were given the paragraph to study, and were then tested for their knowledge of the two orderings. Responses to the remote pairs, A > C, B > D, and A > D, were faster and more accurate than responses to the adjacent pairs, A > B, B > C, and C > D. This was found even when the remote pairs were never presented and had to be deduced from the adjacent pairs. This result is inconsistent with any theory which argues that subjects learn the orderings by storing some subset of the pairs comprising that ordering, as well as with any simple associationistic chaining theory of serial learning. The classical empiricist argument that m e m o r y consists of no more than a set of slightly faded copies of sensory impressions linked together by associations has fallen into disfavor among many contemporary psychologists. Cognitive psychologists have been more receptive to Bartlett's (1932) notion that memories are the result of an active constructive process which subjects perform on the input information, and that the final encoded version of this information may bear little resemblance to the material as it was actually presented. According to Bartlett, incoming information is incorporated into "active, organized settings" called schemata. When asked a question about the presented material, subjects must use these active schemata to reconstruct the required information. In Bartlett's words, "the organism would say, 1 This paper is based on a dissertation submitted to the Department of Psychology at Indiana University in partial fulfillment of the requirements for the doctoral degree. The research was performed while the author was being supported by a PHS terminal year fellowship, and was supported in part by PHS Grant MH16817 to Dr. Frank Restle. I am deeply indebted to Dr. Restle for the continued support he provided in all aspects of this project. 2 Now at the Department of Psychology, Dartmouth College, Hanover, N H 03755. 727 Copyright © 1972 by Academic Press, Inc. All rights of reproduction in any form reserved.

if it were able to express itself: 'This and this and this must have occurred, in order that my present state should be what it i s ' " (p. 202). Unfortunately, Bartlett's conceptualization of the nature of these schemata was, at best, sketchy; and, to date, attempts to clarify the notion have met with only limited success. One such attempt was the proposal (e.g., Miller, 1962; Mehler, 1963) that subjects transform each incoming sentence into its linguistic deep structure or sentence kernel (Chomsky, 1957, 1965), and then store that kernel along with a list of the transformations which would be necessary to regenerate the original sentence from the stored kernel. Mehler (1963) referred to this coding strategy as a schema-plus-correction strategy, with the stored kernel corresponding to the schema and the list of transformations comprising a set of corrections to that basic schema. A large number of studies have been reported which seem to support this linguistic theory of individual sentence memory (e.g., Mehler, 1963; Mehler & Miller, 1964; Gough, 1965; Savin & Perchonock, 1965; Sachs, 1967). It has recently become clear, however, that subjects' information processing strategies extend far beyond merely altering the form of each input sentence and then storing that

728

POTTS

altered form. Subjects trying to encode meaningful verbal material, it seems, do not store individual sentences at all. This was demonstrated clearly in two series of experiments by Bransford and Franks (1971) and Bransford, Barclay, and Franks (1972). During the acquisition phase of these experiments, subjects were presented with a series of sentences, being told to read each for comprehension. After the whole set of acquisition sentences had been presented, subjects were shown another series of sentences, some of which were identical to one of the sentences presented during acquisition, and some of which were not. Their task was to determine whether each test sentence was or was not word-for-word identical to any of the acquisition sentences. It was found that if a test sentence contradicted any information which had been presented during acquisition, subjects were very accurate in recognizing that the sentence had not been presented. As long as the test sentence was not inconsistent with any of the acquisition sentences, however, subjects were unable to make the desired discrimination. Specifically, subjects were unable to distinguish between information which had actually been presented and information which they, themselves, had deduced from their knowledge of the presented information. On the basis of this evidence, it was concluded that subjects do not encode individual sentences at all, neither verbatim nor in terms of their linguistic deep structure representations. Instead, subjects integrate the information presented in related sentences into complex, wholistic ideas. These ideas are then incorporated into subjects' existing cognitive structures or, as Bartlett (1932) called them, schemata. Unfortunately, though these studies do indicate that incoming sentences are not encoded in terms of their linguistic deep structure, they still do not explain how the incoming information is encoded. In the words of Bransford and Franks (1971), "a very important problem . . . concerns the question of what is learned in the above situations. How

can one characterize the nature of the semantic ideas that are acquired ?" (p. 349). What coding strategy could account for the fact that subjects can accurately recount the meaning of a sentence but are unable to distinguish between information which had actually been presented and information which they, themselves, had deduced? One reasonable coding strategy that could account for this result was suggested by Kintsch (1972, p. 274), who noted that it would be very efficient for subjects to delete from memory any information which was redundant in the sense that it could be deduced from other information stored in memory. In what follows, this will be referred to as a deletion theory. This would be an efficient coding strategy for it would allow subjects to reduce their memory load without any corresponding loss of information; subjects could deduce any of the deleted material whenever they needed it. Using this coding strategy, however, subjects would not be able to determine if a particular piece of redundant information had actually been presented or not, for the redundant information would not be present in memory in either case. A second alternative is that subjects make inferences while studying and that these inferences are stored along with the information which was actually presented. Since this would imply that redundant information is stored regardless of whether it was actually presented or not, such a theory could also account for subjects' inability to determine whether a particular piece of redundant information had actually been presented. This theory, which is the antithesis of the deletion theory, will be referred to as an addition theory. The present experiment was designed to test these two alternatives and to compare them to a simple copy theory, which argues that subjects attempt to store the material verbatim. It was decided that transitive relations or linear orderings of the form A > B > C > D would be employed. In all of what follows, the letters A, B, C, and D will be used to represent

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ENCODING OF LINEAR ORDERINGS

the first, second, third, and fourth terms in this ordering, respectively. Linear orderings were chosen for the present study because this type of material enables one to clearly identify redundant information. Specifically, a fourterm series, A > B > C > D, can be broken into six pairs of terms, three of which are absolutely essential to the establishment of the ordering, and three of which are redundant in the sense that they can be deduced from some subset of the necessary pairs. The three necessary pairs, A > B, B > C, and C > D, will be referred to as adjacent pairs since each consists of a pair of terms which are adjacent to one another in the ordering, The three redundant pairs, A > C, A > D, and B > D, will be referred to as remote pairs since each consists of two terms which are separated by at least one other term in the ordering. A second reason for employing linear orderings was the similarity of these orderings to the material employed by Bransford et al. (1972). It was hoped that the conclusions drawn on the basis of the present experiment would generalize to this earlier work. Each subject in the present experiment was given three study and three test trials on each of two four-term series. For one of these relations, only the three adjacent pairs were presented; for the other, all six pairs were presented. Subjects were tested for their knowledge of all six pairs in both conditions, measures being taken of both proportion correct and reaction time. If subjects store exactly what is presented, then when the remote pairs are not presented, performance on these pairs would have to be poorer than performance on the adjacent pairs. Proportion correct would have to be lower because, in order to be correct on the remote pairs, subjects would have to deduce them from the adjacent pairs at the time of test and, thus, could not be correct on the remote pairs unless they remembered the adjacent ones. Since deducing the remote pairs is known to take time (Huttenlocher, 1968; Clark, 1969), reaction time to these pairs

would have to be longer than reaction time to the adjacent pairs. Furthermore, performance on the remote pairs would have to be better when these pairs were actually presented than when they were not, since in the former case subjects would actually store the remote pairs and therefore would not need to deduce them at the time of test. When the remote pairs are not presented, the deletion theory is identical to the copy theory in terms of the predictions it makes regarding what information will be stored. Since there is no redundant information in the presented material, subjects must store exactly what is presented. Thus, in this case, the predictions of the deletion theory are the same as the predictions of the copy theory; performance should be better on the adjacent pairs than on the remote pairs. Since the deletion theory argues that subjects delete from memory any remote pairs which are presented, however, this theory would predict that performance on the remote pairs should not depend on whether those pairs had actually been presented or not. On the other hand, if subjects deduce the remote pairs while studying and then store these remote pairs along with the information which was actually presented, then proportion correct should be higher on the remote pairs than on the adjacent pairs. This is because subjects can be correct on an adjacent pair only if they remember that pair, but can be correct on a remote pair either if they remember that pair or if they remember some subset of the other pairs sufficient to deduce that pair at the time of test. Though proportion correct would be higher on the remote pairs, however, reaction time would still be longer since reaction time to those remote pairs which had to be deduced would serve to raise the overall reaction time to the remote pairs. METHOD

Subjects Subjects were 255 Indiana University undergraduates who participated to fulfill a course requirement. Each participated in one 30-minute session.

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Apparatus The experiment was conducted in the Mathematical Psychology Laboratory at Indiana University. The experimental room was divided into four individual booths, separated by plywood partitions. Each booth contained a solid-state Sony TV receiver and a response box. Mounted on each response box were two microswitch buttons, one marked TRUE and the other marked FALSE. In the first and third booths, the left button was marked TRUE and the right FALSE; in the second and fourth booths, the order was reversed. Subjects responded by pushing one of these buttons, and both the responses and their latencies were recorded automatically by an IBM 1800 computer. The stimuli which subjects responded to were listed on a computer printout for presentation. A closedcircuit TV camera was used to project an image of a single line of this printout onto the four individual monitors. A modified IBM paper puller advanced the printout between presentations. All timing was controlled by the same computer that recorded the responses.

Procedure Subjects were tested in squads of four or less. Prior to the beginning of the main session, subjects were given a brief practice paragraph to learn, followed by a set of four test sentences to answer. This training sequence was designed to enable subjects to become more familiar with the kind of material they would be expected to learn. Following this training sequence, the experimenter read the instructions and then gave each subject a paragraph to study for 1.5 minutes. Subjects were provided with paper and pencil which they could use to take notes while studying. It was made clear that this was optional, however, and that they did not have to take notes if they did not want to. It was also made clear to the subjects that they would not have either the paragraph or their notes in front of them while they were being tested. After this study period, the experimenter collected the paragraphs and note sheets, left the experimental room, and initiated the first sequence of test sentences. This study-test alternation was repeated for a total of three trials. Each test sequence consisted of a set of sentences, presented one at a time, on the TV monitors. Each sentence remained on the screen for 6 seconds. A 1second pause, during which time the screen was blank, was inserted between successive sentences. Though the same set of test sentences was used for each test sequence throughout the experiment, the order of presentation of these sentences was randomly permuted both for each test sequence within a session and for each session.

Subjects were instructed to respond "true" or "false" to each sentence; "true" if the sentence was consistent with the information presented in the paragraph, "false" if it was not. The importance of fast, though accurate responding was stressed. To make fast responding possible, subjects were instructed to hold the response boxes in both hands, with their left thumb over the left button and their right thumb over the right button.

Materials and Design The paragraph learned by subjects in the present experiment was concerned with contests between a bear, a hawk, a wolf, and a deer for dominion over a forest; and between a fish, a frog, a clam, and a duck for dominion over a pond. The paragraph ordered the forest animals linearly on the criterion of intelligence; it ordered the pond animals linearly on the criterion of friendliness. A sample paragraph is presented in Table 1. TABLE 1 SAMPLE PARAGRAPH PRESENTED TO SUBJECTS IN GROUP 2

In a small forest just south of nowhere, a deer, a bear, a wolf, and a hawk were battling for dominion over the land. It boiled down to a battle of wits, so intelligence was the crucial factor. The bear was smarter than the hawk, the hawk was smarter than the wolf, and the wolf was smarter than the deer. On a small pond in the middle of the same forest, another contest for dominion was being waged. The contenders were a frog, a clam, a duck, and a fish. In this case, however, the battle was to be decided by an election, and friendliness was the crucial factor. The fish was friendlier than the frog, the frog was friendlier than the clam, and the clam was friendlier than the duck. In addition, the fish was friendlier than the clam, the frog was friendlier than the duck, and the fish was friendlier than the duck. In the end, each of the battles was decided in its own way and tranquility returned to the area.

For one of the two relations (the "smarter than" relation in Table 1), the ordering was established by presenting only the three adjacent pairs in the relation (A > B, B > C, and C > D). This presentation condition will be referred to as the "not presented" (NP) condition to indicate that the remote pairs (A > C, B > D, and A > D) were not presented. For the other relation (the "friendlier than" relation in Table 1), the ordering was established by presenting all six pairs in the relation, both the three adjacent and the three remote ones. This presentation condition will be re-

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ferred to as the "presented" (P) condition. The specific presentation condition (NP or P) used in presenting each of the critical relations was counterbalanced. Approximately half the subjects were presented only the adjacent pairs in the intelligence relation and all the pairs in the friendliness relation. The remainder were presented only the adjacent pairs in the friendliness relation and all the pairs in the intelligence relation. Subjects were divided into two groups according to the order in which the pairs comprising each of the two relations were presented in the paragraph. For subjects in group 1 (n = 127), the order in which the pairs were presented bore no simple relation to the actual ordering of the terms. For this group, the adjacent pairs in the NP condition were presented in the order C > D , A > B , B > C . Group 2 (n=128) differed from group 1 in that the pairs were presented in an order which did reflect the actual ordering of the terms. For this group, the adjacent pairs in the NP condition were presented in the simple chained order A>B,B>C,C>D. A set of 24 test sentences was used to test subjects' knowledge regarding the information contained in the paragraphs. Half the sentences were true, half were false. Of the 12 true sentences, six were statements of the six pairs presented in the P condition, three were statements of the three adjacent pairs presented in the NP condition, and three were statements of the three remote pairs in the NP condition. Though these last three sentences were true statements which could be deduced from the three adjacent pairs in the NP condition, they represented information which was never explicitly stated in the paragraphs. Each of the 12 false sentences corresponded to one of the true sentences but had the order of the terms reversed. Thus, for each true test sentence, "X is smarter (friendlier) than Y," there was a corresponding false test sentence "Y is smarter (friendlier) than X."

RESULTS Except where explicitly noted, the performance measures presented here were averaged over the true a n d false test sentences corres p o n d i n g to each pair. Statistical analyses were performed using two-tailed sign tests for m a t c h e d samples (Siegel, 1956). F o r each subject, the a p p r o p r i a t e linear c o m b i n a t i o n of his scores o n the various test questions was calculated a n d the sign of the resultant was recorded. I n all cases, the n u m b e r of n o n z e r o scores was sufficiently large to enable the use

of a n o r m a l a p p r o x i m a t i o n , so the results are stated in terms of z scores.

Proportion Correct Data Table 2 presents the m e a n p r o p o r t i o n s correct, averaged over trials a n d groups, on the adjacent pairs a n d o n the remote pairs as a f u n c t i o n of condition. As can be seen, perf o r m a n c e on the remote pairs was superior to TABLE 2 PROPORTION CORRECT ON THE ADJACENT AND REMOTE PAIRS IN EACH PRESENTATION CONDITION

Presentation condition Type of pair tested Adjacent Remote

Remote pairs not presented

Remote pairs presented

.775 .792

.782 .849

performance on the adjacent pairs, even in the N P c o n d i t i o n where these remote pairs h a d never been presented. This difference between p r o p o r t i o n correct o n the adjacent a n d remote pairs was highly significant in b o t h the N P a n d P conditions [z = 3.49, p < .001, a n d z = 7.68, p < .001, respectively]. It should be n o t e d that this superiority on the remote pairs was observed in b o t h groups a n d thus did n o t depend o n the order of p r e s e n t a t i o n of the pairs in the paragraph. P r o p o r t i o n correct on the remote pairs was significantly better when these pairs were actually presented t h a n when they were n o t [z = 3.58,p < .001]; b u t p r o p o r t i o n correct o n the adjacent pairs, which were always presented, did n o t differ significantly as a f u n c t i o n of c o n d i t i o n [z = 1.22, p = .22]. Overall p r o p o r t i o n s correct o n the 24 test sentences for groups 1 a n d 2 were .747 a n d .851, respectively. This difference, tested by means of a t test for i n d e p e n d e n t samples, was highly significant [t(253) = 6.86, p < .001]. Thus, n o t surprisingly, p e r f o r m a n c e was improved by presenting the pairs in a n order

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which reflected the structure inherent in the actual linear ordering of the terms. At this point, it should be noted that overall performance in the present study was quite high. This was essential if a meaningful analysis of the reaction time scores were to be performed. One might expect that with more difficult material, subjects would find it considerably harder to deduce the remote pairs, and that the observed superiority on these pairs might then disappear. This appears not to be the case. One hundred and fifty-three subjects were tested in a replication of the present study. The same design and similar materials were employed (for details, see Experiment [ in Potts, 1971). The paragraph to be learned contained considerably more information, however; and, consequently, overall performance was considerably lower. The resulting proportions correct in this study are presented in Table 3.

the adjacent pairs, even when the remote pairs were never presented. This difference between reaction time to the adjacent and remote pairs was significant in both the NP and P conditions [z = 6.64, p < .001, and z = 8.02, p < .001, respectively]. The effect of conditions was much smaller, though reaction time to the remote pairs was slightly shorter when those pairs were actually presented than when they were not [z = 2.13, p = .03]. Reaction time to the adjacent pairs did not differ significantly as a function of condition [z = 1.63, p = .10]. These effects are illustrated clearly in Figure 1, which shows the improvement in reaction time over trials for the adjacent and remote pairs in each condition. The data for groups 1 and 2 are presented separately. The superiority of the remote pairs is clearly demonstrated on all trials, for both conditions, and in both 5.1

TABLE 3

29

PROPORTION CORRECT ON THE ADJACENT AND REMOTE PAIRS IN EACH PRESENTATION CONDITION OF A REPLICATION STUDY USING MORE DIFFICULT

2.7

MATERIAL

2.5

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Presentation condition oa

Type of pair tested

Remote pairs not presented

Adjacent Remote

.606 .676

Remote pairs presented .633 .726

It can be seen that, far from being diminished, the superiority of the remote pairs was even more pronounced in the replication. The difference between the adjacent and remote pairs was again highly significant in both the NP and P conditions [z=4.54, p < . 0 0 1 , and z = 6.03, p < .001, respectively]. Reaction Time Data

In what follows, only the latencies for correct answers will be given. Reaction time to the remote pairs was shorter than reaction time to

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ENCODING OF LINEAR ORDERINGS

groups. It is also clear that, for subjects in group 2, actually presenting the remote pairs had virtually no effect on reaction times to those pairs. Thus, the slight beneficial effect of actually presenting the remote pairs can be attributed entirely to subjects in group 1, and even in that group the difference decreases after the first trial. Figure 2 presents the mean reaction times as a function of condition and whether the test sentence was true or false. The scores are averaged over trials and groups. It is clear that the profiles for the two conditions are almost identical. This is definitely not the case for the comparison between the true and false sentences, however. For true sentences, reaction times to the three pairs containing the first term, A, in the ordering (A > B, A > C, A > D) were approximately equal, all being considerably shorter than reaction times to the other three pairs. Reaction time to the remaining remote pair, B > D, was next shortest; and reaction times to the adjacent pairs B > C and C > D were uniformly long. The most noticeable difference in the profiles for the false sentences was the dramatic increase in reaction time to the three pairs containing the first term, A, in the ordering. Of these three pairs, reaction time was shorter the more remote the

pair. Interestingly, reaction times to the false sentences, D > C ? and D > B ? were actually somewhat shorter than reaction times to the corresponding true sentences, C > D ? and B > D ? Finally, for the false sentences, reaction time to the test sentence C > B? was considerably longer than reaction time to any of the other pairs. At this point, it should be noted that, though the proportions correct in the present experiment were quite high, they were not perfect. Since the latencies for correct answers were found to be somewhat shorter than the latencies for wrong answers, one cannot ignore the possibility that the observed differences in latencies might reflect only a difference in proportions correct. First, it should be noted that this seems unlikely in the present experiment, for the speed of responding to the individual pairs did not correspond at all closely to the error profiles on the individual pairs. StilJ acknowledging the possibility of bias, however, the trial-3 reaction time scores of the 44 subjects who got all 24 test sentences correct on that trial were examined. It is reasonable that subjects performing this well should have very few, if any, answers correct by guessing. Even when the remote pairs had never been presented, 38 of the 44 subjects had shorter

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FIG. 2. M e a n reaction time to the six pairs as a function o f w h e t h e r the remote pairs were presented (P) o r n o t presented (NP), a n d w h e t h e r the test sentence was true or false. 27

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reaction times to these remote pairs than to the adjacent pairs. Only five subjects exhibited the opposite effect, with one tied score. This difference was, of course, highly significant [z = 4.88, p < .001]. Thus, the trial-3 reaction time scores of these high-performing subjects replicated the results obtained from all the subjects. As a final check for bias, a revised latency score was examined. This revised latency score was designed to give a measure of mean latency for those cases where subjects were responding on the basis of a knowledge of the correct answer. It was arrived at by employing an adaptation of Yellott's (1971, p. 167, Equation 24) correction for fast guesses in a reaction time task. The proportion of errors was used as an estimate of the proportion of correct guesses, and the reaction time to the incorrect answers was used as an estimate of the reaction time on the correct guesses. The conclusions to be drawn from this revised latency score were completely consistent with the conclusions drawn from the unrevised latency scores. This fact, in itself, provides further support for the contention that the latency scores provide a measure of performance which is distinct from the proportion correct data. Since the results using the three latency scores were consistent, only one of the scores, the average latency for correct items, was presented.

Note-taking Data Upon examination of the note sheets, it became immediately apparent that, in taking notes, a large proportion of the subjects had written down the two complete linear relationships which had been presented in the paragraph. Subjects did this by placing the animals, from smartest or friendliest to least smart or friendly, either one above another with the smartest or friendliest on top, or one next to another with the smartest or friendliest on the left. For the purposes of the following analyses, subjects were scored according to whether they ever, on any trial, took notes;

and whether they ever arrived at the correct ordering. Classification of the note sheets was performed by a laboratory secretary who was completely unfamiliar with the design of the experiment. A comparison of the note-taking performance in the N P and P conditions was accomplished by examining the proportion of subjects who, having taken notes on either relation, wrote down the complete linear ordering on any of the three trials. These proportions for the NP and P conditions were .723 and .736, respectively. The difference did not approach significance, z < 1. Thus, condition does not appear to have affected note-taking performance. The differences in note-taking performance between groups 1 and 2 were large and highly reliable, however. The proportion of subjects in group 1 who took notes on at least one of the relations was .937. For group 2, the proportion was only .789. The difference in these proportions, tested by means of a chi-square test (Siegel, 1956), was highly significant [X2(1) = 11.78, p < .001]. Of those subjects who took notes, however, averaging over condition, the proportion who at some time wrote down the correct ordering in groups 1 and 2 were .655 and .812, respectively. This difference was also highly significant [X2(1)=6.74, p < .01]. Thus, it is clear that fewer subjects took notes when the order of presentation of the pairs reflected the actual ordering of the terms in the relation (group 2) than when it did not (group 1). Among those who did take notes, however, subjects were far more likely to arrive at the correct ordering when the order in which the pairs had been presented did reflect the ordering of the terms in the relation. DISCUSSION

Proportion Correct Data Proportion correct on the remote pairs was found to be higher than proportion correct on the adjacent pairs, even when the remote pairs

ENCODING OF LINEAR ORDERINGS

735

were never presented. This result is in direct presented material; the inferences are stored in contradiction to any theory which proposes memory along with the information that was that subjects use the adjacent, pairs to deduce actually presented. the remote pairs at the time of test. All such The simplest model of this type is the additheories require that, in order to establish the tion theory which proposes that subjects truth or falsity of a test sentence referring to a deduce the remote pairs while studying the remote pair, subjects would have to know all material, and then store these remote pairs the adjacent pairs necessary to deduce that along with the adjacent pairs. Such a theory remote pair. Clearly, if this were the case, then could account for the fact that proportion performance on any remote pair could, at very correct was higher on the remote pairs than on best, be no better than performance on the the adjacent pairs for, according to this theory, worst adjacent pair necessary to deduce it. a subject would be correct on an adjacent pair Thus, neither a copy theory nor a deletion if and only if he remembered that pair. A theory is acceptable in light of the present subject could be correct on a remote pair, data, for both propose that when the remote however, either if he remembered that pair pairs are not presented, subjects store only the itself or if he remembered a set of other pairs adjacent pairs which were actually presented sufficient to deduce it. and deduce the remote pairs at the time of test. The deletion theory goes even a step further, Reaction Time Data proposing that when the remote pairs are preThough the addition theory can account for sented, subjects delete them since they repre- the proportion correct results of the present sent redundant information which can be experiment, it can not account for the reaction regenerated whenever necessary. time results. According to this addition theory, It should be noted that, as far as the present some of the correct responses on a particular experiment is concerned, the predictions of a remote pair result from subjects having resimple copy theory are identical to the pre- membered that pair, others result from subjects dictions of any linguistic model which argues having remembered some subset of the other that subjects store the linguistic deep struc- five pairs which enabled them to deduce that tures of the input sentences. This is true be- remote pair at the time of the test. Reaction cause the linguistic surface structure of the time on the former responses should be equal material employed in the present experiment to reaction time to the adjacent pairs; reaction was so similar to the corresponding deep time on the latter responses would have to be structure (all pairs were of the form "A is better longer than reaction time to the adjacent pairs. than B") that storing the deep structure would Clearly, then, this theory could not account consist basically of storing the actual pairs as for the present finding that, regardless of they were presented. Thus, in rejecting a copy whether the remote pairs were actually pretheory, the linguistic model must also be sented or not, overall reaction time to these rejected. remote pairs was shorter than overall reaction On the basis of the present results, then, it is time to the adjacent pairs. clear that subjects memorize neither exactly One modified version of the addition theory what was presented nor the linguistic deep needs to be examined more closely. The shorter structure of the sentences which were pre- reaction time to the remote pairs could be sented, but instead integrate the information accounted for by such a theory if one were prior to the test, drawing conclusions from willing to assume that subjects not only this information at that time. These inferences, generated and stored all six pairs, but also furthermore, do not serve merely to enable ordered these pairs in memory in certain subjects to delete redundant information in the ways. If one assumed, for example, that the

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POTTS

pairs were stored in such a way that the remote pairs were examined first, then one could explain the shorter reaction time to those pairs. Figure 2 reveals that the reaction time results are not that simple; it is not merely the case that reaction time is shorter the more remote the pair. Whatever the reaction time profile, however, this modified addition theory could account for that profile since the theory puts no restrictions on the order in which the pairs can be arranged in memory. Thus, one only needs to postulate that the pair with the shortest reaction time is stored in the first memory slot (and is therefore retrieved first), and so on. Such a theory is, of course, more complex than the simple addition theory described above since it argues that subjects impose a structure on the six pairs. It is also somewhat unsatisfying since the account of the reaction time profiles is entirely arbitrary. Unsatisfying as the theory may be, however, it is necessary to provide more than six data points before the theory can be challenged empirically. These extra data points can be provided by examining reaction times to true and false sentences separately, as was done in Figure 2. While the model can account for any reaction time profile for the six pairs, it would have to predict that the profile for the false sentences should be approximately the same as the profile for the true sentences. This prediction becomes clear when one notes that, to answer a test question, subjects would first have to retrieve the relevant pair (the pair having the same two terms as the test sentence) from memory. This is true regardless of whether the test sentence is true or false. Thus, though the average time required to answer a false sentence might be longer than the average time required to answer a true sentence, the relative ease or difficulty of the six pairs should be the same regardless of whether the test sentence was true or false. As was observed in discussing Figure 2, this was clearly not the case in the present experiment. It should be noted that these reaction time

results contradict not only the copy, deletion, and addition theories, but also any of the class of theories which would propose that subjects learned the linear orderings by storing some subset of the pairs which comprised that ordering. According to any such theory, subjects could still be correct on a particular remote pair in only one of two ways; by remembering the pair itself, or by remembering a set of other pairs sufficient to deduce that remote pair at the time of test. Any such theory, then, would have to share with the addition theory the inability to account for the fact that reaction time on the remote pairs is shorter than reaction time on the adjacent pairs. Thus, it appears that in trying to learn the transitive relations in the present experiments, subjects did not store the actual pairs at all. Instead, in the process of actively manipulating the presented material, they must have changed its form altogether. On the basis of subjects' note-taking data, it is clear that a large number of subjects used the pairs that were presented to arrange or order the terms serially, placing the four terms one next to each other from top to bottom or from left to right. Having worked to establish this sequential arrangement, it is reasonable that the modified form in which subjects stored the information is this sequential arrangement, that is, the actual ordering of the four terms itself. This suggestion is consistent with the observed effects of the order of presentation of the pairs of terms. Several studies have reported that varying the order of presentation of the adjacent pairs comprising a linear ordering drastically affects the ease with which subjects are able to establish that ordering (Hunter, 1957; DeSoto, London, & Handel, 1965; Huttenlocher, 1968; Handel, DeSoto, & London, 1968). The note-taking results of the present experiment are consistent with this conclusion in that, of those subjects who took notes, the proportion who got the correct ordering was substantially higher in group 2 where the pairs had been presented in an order which reflected the actual ordering of the terms

ENCODING OF LINEAR ORDERINGS

in the series. The fact that a larger proportion of subjects took notes in group 1 could be taken as an indication that subjects in that group felt more of a need to take notes since the establishment of the ordering was more difficult due to the haphazard order in which the pairs were presented. It follows that the improvement in proportion correct observed in going from group 1 to group 2 may have been due directly to the ease with which the linear ordering was established by subjects in group 2. Other researchers have also noted the tendency for subjects to order terms linearly even when not specifically required to do so (DeSoto, 1960, 1961 ; DeSoto & Bosley, 1962; Kuethe, 1962; Henley, Horsfall, & DeSoto, 1969). In light of his results, DeSoto concluded that the linear ordering acts as a powerful schema in directing the analysis and encoding of certain types of information. The results of the present experiments would certainly appear to support this contention. Many questions still remain, however, regarding the actual form of this stored serial arrangement.

Associative Chaining Hypotheses The most prominent theory regarding the process involved in learning a serial list is the associative chaining hypothesis (consult Young, 1968). This theory can be eliminated immediately on the basis of the present results. The predictions of a theory which argues that subjects deduce the remote pairs by establishing a chain of associations between various adjacent terms are the same as the predictions of the deletion the6r.y. Neither theory can account for the superior performance on the remote pairs that was observed in the present experiment. The addition of a remote association assumption does not help, for the resulting theory makes the same predictions as the addition theory. Though both theories can account for the higher proportion correct on the remote pairs, neither can account for the fact that reaction times to these remote pairs are shorter.

737

Rating Scale Hypothesis A more viable alternative is a rating scale theory which argues that subjects learned the orderings in the present experiments by placing the four terms on imaginary scales of "smartness" and "friendliness." On such a scale, quantitative differences in smartness or friendliness between two animals are represented by spacial distances between those terms on the scale; and the farther apart on the scale two terms are, the higher the proportion correct on the pair comprised of those terms. This theory could easily explain the higher proportion correct on the remote pairs, since the terms comprising these remote pairs would have to be placed farther apart on the scale than the terms of the adjacent pairs necessary to deduce them. While this model, as it stands, makes no predictions regarding the reaction time data, it could be modified to account for this data by the addition of various decision criteria. It is questionable, however, whether any such model could account for the obtained difference in reaction time profiles for true and false sentences, or for the fact that the observed reaction times were not a simple decreasing function of remoteness.

End-Term Anchoring It has been proposed by several researchers (Wishner, Shipley, & Hurvich, 1957; Feigenbaum & Simon, 1962; DeSoto & Bosley, 1962; DeSoto et al., 1965; Handel et al., 1968) that serial lists are learned from the end points inward and that the first and last terms in the list share a special status in serving as "anchors" for the other terms in the list. If one accepts that subjects learn the endpoints first, and are therefore more confident of the position of these terms in the list, then one can account for a large portion of the reaction time data presented in Figure 2. To account for this data, one needs only to argue that subjects examine each of the terms in the test sentence successively, checking if each is an end term, A or D. If it is, subjects

738

POTTS Input / first term / in test /

T

Is it the first term X (A)in the ordering ? /

YES

l

Is it the last term X (D) in the ordering ? /

\

YES

Tnput /

\second term/ \ in test /

Is it the first term (A}inthe ordering 7 /

YES

I

NO

_

YES

/ Is it the last term X (D) in the ordering ? /

l N° L_ Y E S

/

X Is it the

"True"

"C"term?>

NO

"False"

J FIG. 3. Flow diagram depicting a possible strategy for answering test questions.

can respond immediately without processing the rest of the ordering. For the four-term series employed in the present experiments, the only term not containing such an end term is the pair B > C; so, as was observed, reaction time to the two test questions (B > C? and C > B ?) relating to that pair should be noticeably long. A flow chart presenting one such processing strategy in detail is shown in Figure 3. According to this strategy, a subject first

examines the first term in the test sentence and asks himself if it is the first term (A) in the ordering. If it is, he can respond immediately, indicating that the sentence is true. Thus, reaction time to the true test sentences A > B ?, A > C?, and A > D ? should be uniformly short, as was observed. I f the first term in the test sentence is not the first term in the ordering, the subject then asks if the first term in the test sentence is the last term (D) in the ordering.

ENCODING OF LINEAR ORDERINGS

If it is, the subject can again respond immediately, indicating that the test sentence is false. Thus, reaction time to the false sentences, D > A ? , D > B ? , and D > C ? , should be uniformly short, though longer than reaction time to the test sentences A > B ?, A > C ?, and A > D ? At this point, the model's predictions deviate from the obtained results in that reaction time to the test sentence D > A? was found to be shorter than reaction time to the test sentences D > B ? or D > C ? One explanation for this discrepancy is that the reaction time data from the present experiments is based on group averages, and thus the profiles represent composite profiles rather than the profile for any one given subject. It may be that not all subjects employ the same strategy for answering the questions. Assume for the moment that all subjects employ the first decision criterion as it was described above. This seems a reasonable assumption given the extremely short reaction times to the test sentences A > B ?, A > C?, and A > D ? Having failed to meet that criterion, however, assume that, instead of staying with the first term in the test sentence, some subjects go immediately to the second term and, as the second decision point, ask themselves if that second term in the test question is the first term in the ordering. These subjects will be able to correctly respond "false" to the test sentences D > A ?, C > A ?, and B > A ? at the second decision stage. Assuming that half the subjects proceed according to the first strategy and half proceed according to the second, it follows that all subjects can answer the test sentence D > A ? in the second processing stage. A given subject can answer only two of the four questions, C > A ?, B > A ?, D > B ?, D > C?, in the second stage, however; the other two cannot be answered until some later stage. Thus, as was observed, the composite (averaged over subjects) reaction time should be shorter on the test sentence D > A? than on any of the other four test sentences. Of course, this is a highly speculative

739

account. The theory can easily account for the superior performance on the remote pairs which was observed in the present experiments, but it has an interesting characteristic in that it argues that this high performance on the remote pairs is related only indirectly to the remoteness of the pair. According to this theory, performance is better on the remote pairs because the remote pairs are more likely to contain one of the end terms. Specifically, with a four-term series, all three remote pairs contain at least one end term; and one pair, A > D, contains both. It would prove informative to replicate the present experiment using an ordering which consisted of more than four terms, so that at least one remote pair would contain no end term. Also, enough data should be collected from each subject to enable one to examine the reaction time profiles of individual subjects. The present experiment was designed to determine the strategies subjects employ when trying to learn meaningful verbal material. The material to be learned consisted of linear orderings presented in paragraph form. Performance, both proportions correct and reaction times, was better on redundant information, which could be deduced, than it was on information which was necessary to establish the ordering. Surprisingly, this was the case even when the redundant material was never presented. This result was shown to be inconsistent with a number of possible theories regarding how subjects encoded the information. It should be noted that, though highly reliable in the present experiment, this result is not obtained by all researchers. Specifically, Frase (1970) has examined the learning of settheoretic relations and has found that proportion correct on the deducible information is noticeably poorer than performance on the necessary information. Frase's experiments differed from the present experiments in several procedural points, however, as well as in the type of information employed. Examples of such possibly important procedural differences are the type of test employed, the

740

~OTTS

retention interval, and the presence or absence of irrelevant information in the paragraph. Further experiments are necessary to determine the exact reasons for the differing results. Such experiments should go far towards clarifying the strategies employed by subjects attempting to remember meaningful verbal material.

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HANDEL, S., DESoTo, C. B., & LONDON,M. Reasoning and spatial representations. Journal of Verbal Learning and Verbal Behavior, 1968, 7, 351-357. HENLEY, N. M., HORSFALL, R. R., & DESOTo, C. B. Goodness of figure and social structure. Psychological Review, 1969, 76, 194-204. HUNTER,I. M. L. The solving of three-term series problems. British Journal of Psychology, 1957, 48,286298. HUTTENLOCHER, J. Constructing spatial images: A strategy in reasoning. Psychological Review, 1968, 75, 550-560. KINTSCH, W. Notes on the structure of semantic memory. In E. Tulving and W. Donaldson (Eds.) Organization of memory. New York: Academic Press, 1972. Pp. 247-308. KUETHE,J. L. Social schemas. Journal of Abnormal and Social Psychology, 1962, 64, 31-38. MEHLER, J. Some effects of grammatical transformations on the recall of English sentences. Journal of Verbal Learning and Verbal Behavior, 1963, 2, 346-351. MEHLER, J., & MILLER, G. A. Retroactive interference in the recall of simple sentences. British Journal of Psychology, 1964, 55, 295-301. MILLER, G. A. Some psychological studies of grammar. American Psychologist, 1962, 17, 748-762. PoTxs, G. R. A cognitive approach to the encoding of meaningful verbal material. Indiana Mathematical Psychology Report Series, Report No. 71-7, 1971. SACr~S, J. S. Recognition memory for syntactic and semantic aspects of connected discourse. Perception and Psychophysics, 1967, 2, 437-442. SAVIN, H. B., & PERCHONOCK,E. Grammatical structure and the immediate recall of English sentences. Journal of Verbal Learning and Verbal Behavior, 1965, 4, 348-353. SIEGEL, S. Nonparametric statistics for the behavioral sciences. New York: McGraw-Hill, 1956. WISHNER, J., SHIPLEY, T. E., • HURVICH, M. S. The serial-position curve as a function of organization. American Journal of Psychology, 1957, 70, 258262. YELLOTT,J. I., JR. Correction for fast guessing and the speed-accuracy tradeoff in choice reaction time. Journal of Mathematical Psychology, 1971, 8, 159-199. YOUNG,R. K. Serial learning. In T. R. Dixon and D. L. Horton (Eds.), Verbal behavior and general behavior theory. Englewood Cliffs, N J: Prentice-Hall, 1968. (Received March 21, 1972)