The effects of strategy instructions and memory on concept attainment

JOURNAL

OF VERBAL

The

LEARNING

Effects

AND VERBAL

BEHAVIOR

of Strategy Concept

7,831-837

(1968)

Instructions Attainment1

and Memory

on

JOE L. BYERS Michigan State University, East Lansing, Michigan 48823 ROBERT E. DAVIDSON University of Wisconsin, Madison, Wisconsin 53706

WILLIAM D. ROHWER, JR. University of California, Berkeley, California 94720

One hundred twenty Ss attained three conjunctive conceptsunder varying conditions of strategy instructionsand memory aids. The hypothesisunder test was: the conservative focusing strategy facilitates concept attainment performance by reducing the strain on the S’s memory. This hypothesiswas tested in a factorial design with independent groups in which two variableswere manipulated: strategy instructions, present or absent; and memory aid, presentor absent.Support for the hypothesiswasevidencedby an interaction. Strategyinstructions were related to performance only when there was no memory aid. Two recent experiments have produced contradictory results regarding the efficiency of the conservative focusing strategy on concept-attainment (CA) performance. Klausmeier (1964) reported that a group instructed in the use of conservative focusing required reliably fewer trials to reach criterion than a group not given such instructions. In the second experiment, Rundquist et al. (1965) used a transfer design to analyze the effects of strategy training on CA performance. Three groups of Ss were given training on aspects of CA ranging from stimulus familiarization to instruction in the use of conservative focusing. On a series of common CA transfer tasks the average performance of these groups compared with a no-training

control group gave no evidence of differential transfer. Although the discrepancy in the results of these studies seems difficult to resolve, Rundquist et al. noted that different memory requirements in the two experiments may have been responsible. In the Klausmeier study the Ss were given no external memory aids for stimuli previously tested, while in the Rundquist et al. study the Ss were allowed to mark each tested stimulus as a positive or negative instance. Thus in the latter experiment Ss were given a memory aid as well as strategy instructions, while in the former only strategy instructions were available. These procedural differences may have resulted in the different conclusions drawn from the data of the experiments. For normal adults it seems that the probable 1 This work was carried out at the Institute of Human Learning, University of California, Berkeley, major function of strategy instructions is to which is supported by grants from the National Science reduce the memory requirements of CA tasks. Foundation and the National Institutes of Health. Further, it is proposed that any procedure Partial financial support was also receivedfrom the National Institute of Mental Health Grant No. resulting in a reduction of task memoryrequirements will facilitate CA. For example, MH 10201-01. 831

832

BYERS, DAVIDSON, AND ROHWER

performance ought to be improved when Ss are provided with a method for recording the status (i.e., relevant or irrelevant), of each attribute as it is designated. The present experiment was undertaken to test the memory-function explanation of strategy instructions and to extend the explanation to another variable, attribute memory. There were three dichotomous independent variables which were varied in a complete factorial design. They were: the presence or absence of stimulus-display memory; the presence or absence of explicit instructions; on conservative focusing, and on the use of attribute memory. Two simple interactions were of special interest. The interaction of strategy instructions and stimulus-display memory was predicted to be significant, i.e., when there is no stimulus-display memory there should be a reliable difference in the performance between Ss given strategy instructions and those not given strategy instructions, with the former being superior. On the other hand, when stimulus-display memory is present, there should be no difference between the strategy-instruction group and the nostrategy instruction group. The other interaction of interest is between strategy instructions and attribute memory. The nature of this interaction should parallel the previous case, i.e., strategy instructions should be facilitative only under conditions where attribute memory is absent. METHOD Tusk and Apparatus. In this experiment the CA tasks required that Ss discover the E-defined rule for categorizing a set of flgural stimuli into two subsets, positive instances and negative instances. The correct concept rule described the common characteristics of all the stimuli in the subset of positive instances. The stimulus materials for the CA tasks were generated by making all possible combinations of eight bileveled figural attributes. All possible combinations of these eight attributes generate a population of 256 stimulus cards. A selected sample of 64 cards was drawn from this population. For this experiment one card was arbitrarily designated as the focus card (the first positive instance, given to the S before the start of’each

problem), and then the remainder of the sample was selected so that the number of cards differing from it (the focus card) in only one attribute, approximated the number differing in two or more attributes. The number of stimulus cards in the sample differing from the focus card in one attribute was eight; in two attributes, eight; in threeattributes, 10; in four attributes, 9; in five attributes, 13; in six attributes, 8; in seven attributes, 6; and in eight attributes, i. The focus card itself accounts for the one remaining card in the sample. The 64 cards were then affixed to the stimulusdisplay board in a square array. Care in placement was taken so that no systematic arrangement appeared in the cards once they were on the board. The completed display board was then placed on the face of the Ss’ display panel.* When the display board was in place, two combination response-key feedback lights protruded through the board immediately below each stimulus card. A red feedback light was associated with negative instances and an amber feedback light was associated with positive instances. The apparatus used in the experiment consisted of a stimulus board on which all stimulus cards were constantly available to the Ss. Each time S tested a stimulus card by pressing either response key located immediately below it, the apparatus informed him (by turning on the red or amber lamp) if the stimulus was a negative instance or positive instance. For half of the Ss (those assigned to the stimulus-display memory condition), the feedback lamps under those stimulus cards that had been tested remained lighted throughout the problem. For the Ss in the no stimulus-display memory conditions, the lamps went out immediately after the Sremoved his finger from the response key. The S used the following procedure in offering an hypothesis about the concept rule. There was a small button on the lower left side of the display panel which, when pressed, informed the E that the S was about to offer an hypothesis and, at the same time, placed the apparatus in hypothesis mode. The S could then set the switches at the bottom of the display panel to indicate what he believed the rule to be. There were eight three-position switches, one for each stimulus attribute and labeled with appropriate names. The switch labeled shape, for example, could be moved to the up position, indicating all positive instances must have circular figures; to the down position, indicating that all positive instances must have elliptical figures; or left in the center position, indicating that the attribute of shape was irrelevant. In offering an hypothesis, the S had to make a decision indicating the position of each of these switches. When he had completed “writing” his hypothesis, he tested its accuracy by pressing a small button on the lower side * A complete description of the apparatus used may be found in Byers et at. (1964).

833

MEMORY AND STRATEGY of the display panel just to the right of the last of the hypothesis switches. Invalidation or validation of an hypothesis followed immediately upon the pressing of “query” button and was indicated by one of two adjacent lamps located at the bottom of the display panel. The hypothesis switches also served as a means for manipulating the attribute-memory variable. Those Ss in the attribute-memory condition were instructed to set a switch each time they determined the status of an attribute. Used in this way, the S “wrote” his hypothesis as he tested stimuli. The Ss not in an attributememory condition were not permitted to use the switches for any purpose other than hypothesis offering. For both groups, each time an incorrect hypothesis was offered, the E erased it completely, i.e., reset all switches to the center position. Concept complexity is an independent task variable that has repeatedly influenced CA performance (Haygood and Bourne, 1965). In order to obtain greater generality of the results for this experiment, concept complexity was varied. A series of three conjunctive concepts, with varying numbers of relevant and irrelevant attributes, was defined: (a) two relevant and six irrelevant, (b) three relevant and five irrelevant, and (c) four relevant and four irrelevant. In order to obtain the maximum information from the Ss available, repeated measures were used. Thus each S was required to attain all three concepts. The final experimental design was a 2 x 2 x 2 factorial design within which was a random replicated 3 x 3 Latin square. The entire experiment was replicated four times, yielding 45 observations on which to base the comparisons among the means of the eight principal treatment groups. Procedure. The Ss were assigned at random to one of eight basic treatment conditions and further randomly assigned to one of three sequences of the threeconjunctiveconcept problems. When S appeared at the laboratory, he was given a notebook which contained the general instructions for the experiment. These instructions described the attributes of the stimuli and the nature of conjunctive concepts. The S was informed that the rule or concept he was seeking might have from one to eight relevant attributes. The instructions indicated that he could determine the concept by testing the stimulus cards on the board in front of him. The E then asked the S to select several positive instances of the concepts, “circles” and “two ellipses.” If the S had trouble following this instruction, the E aided him by paraphrasing the instructions in which positive instances were described. Next the E caused the S to “write” the hypotheses for the concepts of “circles” and “two ellipses” by setting the appropriate switches. The S was told the task would always begin with the designation of one positive instance (the focus card),

by the E, after which the S could test any other cards he wished. When he tested a card by pressing the response key, the machine would inform him whether or not the card tested was a positive instance or negative instance. He was to determine the concept from this information. His job was to determine the correct rule with as few card choices (trials) as possible. Up to this point in the instructions all Ss were treated alike. Instructions given to Ss assigned to strategy groups were designed to teach conservative focusing as a procedure for the selection of stimuli. These instructions also stressed how to make correct inferences about attribute status from both positive and negative instances. Naturally individuals assigned to conditions not given strategy instructions were told nothing about what cards to select for test or how to make inferences from the test results. Subjects assigned to the attribute-memory conditions were told how to use the hypothesis switches to mark or designate the status of attributes when they become known. Immediately after receiving the instructions required for the treatment conditions to which they had been assigned, Ss began the series of three concept problems, No additional instructions were given nor were questions answered. The E kept a record of the total number of trials to criterion and the sequence of card choices. The criterion was the correct statement of the rule for describing positive instances. All Ss were taken to criterion on all three concept problems. Any incorrect hypotheses were recorded and the trial noted on which they occurred. Subjects. One hundred and twenty college-age students served as Ss in the experiment. Sixty were paid an hourly wage and 60 served as part of course requirements in an introductory course in Educational Psychology. Both groups were distributed evenly over all treatments. RESULTS AND DISCUSSION

Since two of the three principal independent variables in this experiment were manipulated solely by means of instructions, it is necessary to estimate the extent to which Ss followed the instructions in order to evaluate properly the effects of the variables on concept attainment. Relatively independent (from trials-tocriterion) measures of the effectiveness of the instructional variables were available. For trials one to eight of each S on each problem the percentage of conservative focusing, and percentage of attribute-memory trials were determined. If the instructions were completely

BYERS, DAVIDSON, AND ROHWER

834

effective the mean percentage for both measures should not have deviated reliably from 100%. Analyses of these two measures revealed that both differed reliably from 100x, indicating that our manipulation was not completely successful. However, these same analyses showed that there were reliable differences in the mean percentages of conservative focusing and attribute-memory use between the groups instructed and those not instructed. The trials-to-criterion data were subjected to a complete analysis of variance, in which all

related to the experiment was an uninterpretable complex interaction among the three principal independentvariables and sequences. Table 1 presents the means for the main effects and interactions of strategy instructions, attribute memory and stimulus-display memory. As expected, the main effect of strategy instructions and stimulus-display memory were significant, F(1, 96) = 24.70, p < .05 and F (1,96) = 30.43, p < .05, respectively. This table shows that the presence of either conservative-focusing instructions or stimulus-display memory has the effect of improving CA performance. The main effects

TABLE MEAN

TRIALS

TO CRITERION

1

FOR THE EIGHT

EXPERIMENTAL

GROUPS

Task conditions

Instructions

Stimulus-display memory

Conservative focusing Attribute memory No attribute memory

10.8

No conservative focusing Attribute memory No attribute memory

16.4

Total

13.6

No stimulus-display memory 18.0

9.3 12.3

3 Due to the fact that the variance-covariance matrices failed to have the required form, all tests involving repeated measures were made with the conservative test suggested by Winer (1962, p. 123); in this case 1 and 119 degrees of freedom.

14.4 16.0 20.0

36.2 16.1 16.7

identifiable sources of variance were computed and removed to yield the best estimate of error variance for the hypotheses to be tested. There were two appropriate error terms: one for tests not involving repeated measures, this was the &/groups mean square and had a value of 539.840 with df= 96; and one for t:sts involving repeated measures, called the residual, with a value of 294.900, df = 144.3 The only reliable source of variance not

Total

26.3 35.9 36.6

27.1

of these two variables account for about 30 % of the observed variability among Ss. Their interaction, which is also significant, F(l,96) = 6.69, p < .05, accounts for an additional 3.5 %. Post hoc SchefE comparisons indicate that the only meaningful significant difference among the means in this interaction is between the groups receiving and not receiving strategy instructions within the no stimulus-displaymemory condition. This observation confirms the prediction of the experiment. When stimulus-display memory was not present, instructions on how to use conservative focusing reliably improved S’s performance; indeed, it reduced trial-to-criterion by

MEMORY

AND

about half, replicating the effect reported by Klausmeier (1964). On the other hand, when stimulus-display memory was available, the instructions on strategy use resulted in no reliable difference in performance, substantially replicating what Rundquist et al. (1965) reported. Neither the main effects nor any of the interactions involving attribute memory were significant. It is not clear whether the variable’s failure to affect performance should be attributed solely to the failure to achieve successful manipulation, or to the fact that the variable in fact is not related to CA performance. One additional observation may be made. If the attribute-memory variable is related to performance and our failure to observe it in this experiment is due to its unsuccessful manipulation, then the effect must be a rather small one. Such a conclusion seems justified, for the strategy-instruction variable did not receive a fully successful test although it clearly contributed to S’s performance. The present status of the attribute-memory variable is ambiguous at best. Since each S attained three successive concepts in a counterbalanced order, it was possible to assessthe presence or absence of an interconcept practice effect. The data showed the presence of such an effect, F(1, 119) = 7.20, p < .05.3 Mean trials-to-criterion was 25.0 on the first problem, 19.3 on the second, and on the final problem, 16.8. A Scheffe contrast indicated that there were no differences in performance between problems two and three, but both were significantly superior to problem one. As expected, concept complexity had a significant main effect, 41, 199) = 5.39, p < .053, on performance as well as a significant interaction with strategy instructions, F-(1, 119) = 4.99, p < .053. The main effect of concept complexity can best be interpreted by looking at the simple effects of this variable under varying strategy conditions. Scheffe contrasts reveal that when Ss are not given conservative-focusing instruc-

835

STRATEGY

tions, performance on concept problems involving four relevant attributes is significantly poorer than on problems with only two relevant attributes. Although the increase in relevant information in this experiment is confounded with a decrease in irrelevant information, the relationship is nevertheless similar to evidence reported by Bulgarella and Archer (1962), Walker and Bourne (1961), and Byers and Davidson (1968). The effects of concept complexity on CA performance given strategy instructions are quite different. Scheffe tests among these means failed to show any meaningful comparisons to be significant. Therefore, it must TABLE 2 MEAN

TRIALS TO CRITERION ComLmm

AS A FUNCTION OF CONCEFT AND STRATEGY INSTRUCTIONS

(Each mean based on 60 observations.) Number of relevant attributes 2

3

4

Strategy instructions No strategy instructions

13.0 20.2

16.3 24.9

13.9 33.9

Overall conceptcomplexity means

16.6

20.6

23.9

be concluded that giving Ss instructions on how to use the conservative-focusing strategy disrupts the normal relation between the amount of relevant information and CA performance, at least over the range of values used in this study. It appears as if conservativefocusing instructions render all degrees of complexity roughly equivalent. Although the concept complexity by stimulus-display memory interaction was not significant, its appearance was very similar to the concept complexity by strategy interaction; i.e., mean trials-to-criterion with varying amounts of relevant information under stimulus-displaymemory conditions are virtually equal while

836

BYERS,

DAVIDSON,

under no stimulus-display-memory conditions the mean trials run from 20.8 for two relevant to 33.0 for four relevant attribute problems. Had the stimulus-display memory by concept complexity interaction been reliable it would have replicated the findings of Bourne, Goldstein and Link (1964). This experiment was undertaken to evaluate an explanation for a discrepancy in the results of two previously reported experiments involving the effects of strategy instructions on CA performance. The data clearly support the interpretation that the discrepancy in the effects of strategy instruction on CA performance noted by Rundquist et al. (1965) is due to the procedural differences between their experiment and Klausmeier’s (1964). Consequently, for conjunctive concepts, the main function of conservative-focusing strategy is to reduce the memory requirements of the CA task. The results of the comparisons among means of groups having varying degrees of concept complexity further demonstrate this conclusion. Optimal CA performance would be predicted to occur under conditions which brought about the rapid designations of all stimuhts attributes and the retention of a list of those found to be relevant. Byers and Davidson (1968) have argued that the reason CA performance shows a generally monotonic increasing relationship to amount of relevant information is that the verbal chain constituting the concept hypothesis gets longer as the number of relevant attributes increases. The conservative-focusing instructions cannot, of course, reduce the length of the chain, but they can provide the S with a systematic means of acquiring it, which minimizes the effect of retroactive and proactive interference on chain retention. When an S makes a card choice other than one based on conservative focusing, there is a high probability (with conjunctive concepts) that the card tested will be a negative instance and, therefore, he is usually not given unequivocal information about the relevance

AND

ROHWER

of the varied attributes. The S must then make additional trials to disambiguate the varied attributes. During these additional trials, the chances for proactive interference with current information from preceding trials and retroactive interference from current trials on the retention of information derived from earlier trials increases. This results in poorer retention of the attribute-status-list and requires increased amounts of overlearning (more trials) to overcome the interference. On the other hand, when Ss are taught to use conservative focusing, they make choices which unequivocally designate each attribute in succession and thus require fewer choices to develop the attribute-status-list. This reduction in the number of card choices also lessens the opportunity for the operation of both proactive and retroactive interference. The availability of stimulus-display memory should also reduce the opportunities for interference in the learning of the attributestatus-list. When all tested concept instances remain available to the S, the necessary information for the attribute-status-list is continually present. Without stimulus-display memory the Ss must rely on their memories for the acquisition and retention of the attributestatus-list and any device they can generate to improve on it. As the data indicated, when Ss used the conservative-focusing strategy they could effectively replace the stimulus-display-memory loss. Without either conservative-focusing instructions or stimulusdisplay memory their CA performance showed a significant reduction in efficiency. REFERENCES B~LJRNE,L.E., GOLDSTEIN,S.,ANDLINK, W.E.Concept learning as a function of availability of previously presented information. J. exp. Psychol., 1964, 67,4394l8. BULGARELLA, R. G., AND ARCHER, E. J. Concept identification of auditory stimuli as a function of amount of relevant and irrelevant information. J. exp. Psychol., 1962,63,2X-257. BYERS, J. L. Strategies and learning set in concept attainment. Psychol. Reports, 1963, 12, 623-634. Errata Psychol. Reports, 1963, 13, 2.

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An apparatus Psycho1

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for concept attainment

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1964,14,759-173.

J. L., AND DAVIDSON, R. E. Relevant and irrelevant information in concept attainment.

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L. E. Attribute- and aspects of conceptual behavior. Psychol. Rev., 1965,72, 175-195. KLAUSMEIER, H. J. The effects of a principle and of instructions that incorporate three types of information upon efficiency of concept attainment. Amer. Psychol., 1964,19,464.

HAYGOOD,

R. C., AND B~URNE,

rule-learning

E. A., FORD, J. D., CHESLER, D. J., W. D., AND BRAUNSTEIN, H. M. Preparation for problem solving: structural vs. strategypretraining. U.S. NavalPersonnel Research Acfivity, San Diego, Calif., 92152, Tech. Bull. STB 66-1,1965. WALKER, C. M., AND BOURNE, L. E. The identification of concepts as a function of amounts of relevant and irrelevant information. Amer. J. Psycho& 1961,74,410-417. RUNDQUIST, ROHWER,

WINER, J. B. Statistical Design, New York,

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McGraw-Hill,

(Received September 18,1967)

in Experimental

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