Isolation of massed-and distributed-practice items

.\lemo'y and Cognition /973. 1'01. /. 77-79

Isolation of massed- and distributed-practice items* DAVID G. ELMES, LESTER W. SANDERS, and JOHNC. DOVEL Washington and Lee University, Lexington, Virginia 24450 In four experiments, massed-practice (MP) or distributed-practice (DP) items were isolated from other items in a list presented either visually or auditorially for free recall. For three independent groups, the first, second, or both presentations of an item were isolated. Locus of isolation had a marginal influence on recall. When MP items were isolated, they were recalled better than DP items. Isolating the DP items enhanced the MP·DP effect. The results are congruent with the idea that the MP-DP effect in free recall results, in part, from differential rehearsal.

Distributed practice (DP) on verbal events presented for free recall results in higher levels of recall than does massed practice (MP). In addition, a frequent finding has been that the recall of DP items increases as the lag (separation) between repetitions increases. Support for these two assertions comes from several experiments that differed widely along such parameters as rate of presentation, frequency of item presentation, and kind of to-be-remembered items (e.g., D'Agostino & DeRemer, 1972; Elmes, Greener, & Wilkinson, 1972; Melton, 1970; Underwood, 1970). The two most viable explanations of the MP-DP effect (Elmes et al, 1972) seem to be the differential-rehearsal (e.g., Underwood, 1970) and the variable-encoding (e.g., Melton, 1970) hypotheses. According to the differential-rehearsal notion, the MP·DP effect occurs because Ss pay less attention to the second MP presentation than they do to the second DP presentation. The variable-encoding hypothesis asserts that more new information is encoded on successive presentations in DP than in MP and that this variable encoding increases as lag increases. Since both of these hypotheses refer to aspects of the storage process, it isnot surprising that current evidence indicates that both differential rehearsal and variable encoding contribute to the MP·DP effect (D'Agostino & DeRemer, 1972): MP-DP differences in recall result from differential rehearsal, whereas improved recall with increases in lag results from variable encoding. The present experiments are addressed to the differential-rehearsal account of the better recall observed under DP than under MP.Both Rundus (1971) and Shaughnessy. Zimmerman, and Underwood (1972) report that Ss rehearse MP items less than they rehearse DP items. It follows, therefore, that increased rehearsal of MP items should attenuate the MP-DP effect. Conversely, increased rehearsal of DP items should *This research was supported by a R. E. Lee Research Grant. Portions of these data were presented by the second author at the meetings of the Virginia Academy of Science, Lexington, May 1972. Requests for reprints should be sent to David G. Elmes, Department of Psychology. Washington and Lee University. Lexington. Virginia 24450.

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enhance the MP·DP effect. Differential rehearsal was effected in the present studies by isolating the appropriate MP or DP items from the remaining items in the list. The assumption behind the use of isolation as a rehearsal variable is that the isolation effect in free recall seems attributable, primarily, to the increased rehearsal of the isolated items (Waugh, 1969). Although it is possible that isolating an item increases its accessibility because the isolating stimulus provides additional retrieval cues, Waugh's data show that isolation serves to enhance the amount of attention paid to the isolated event. In the present studies, all items received two presentations. Thus, the first, second, or both presentations of an item could be isolated. Such a manipulation seems to provide a test of the possibility that differential rehearsal of the second presentation is the important factor in the MP·DP effect. METHOD The design and procedure of the four experiments were highly similar, so a general description will be presented first and then the differences among the studies will be described. The design can be viewed as a two-factor mixed design (3 by 3). There were three independent groups in each study defined by the isolation of the first. second, or both presentations of the MP or DP items of interest. The within-Ss variable was item type: isolated (I) and nonisolated (N) items of one type (MP or DP) and N items of the other. The group designations were IN. N!. and II. respectively, for the Ss having the first, second. or both presentations isolated. Each S was presented a 68-event 34-item list in which each high-frequency noun (at least 50 per 1.000,000 words according to Thorndike & Lorge. 1944) was presented twice. Eight buffer events began and ended each list to minimize primacy and recency effects on the items of interest. Within each list. there were 12 items of interest: e.g.. when MP items were isolated. there were 3 MPI items. 3 ~IPN items. and 6 DPN items. and when DP items were isolated. there were 3 DPI items. 3 DPN items. and 6 MPN items. The DP items had a repetition lag of 5. and the filler items had various lags including Lags 0 to 5. To minimize serial position effects. 4 DP and 4 ~IP items were presented in the middle serial positions of each third of the list. One isolated item occurred in each third of the list, Item counterbalancing assured that each item of interest served as a DP item for half the Ss and as an ~IP item for the remaining Ss. The Ss were tested in small groups, The items were presented

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ELMES. SANDERS A~D DOVEL

The mean percent recalled of each item .typc in each group of Experiment 1 appear in' the top portion of Table 1. It is apparent that the different types of items were recalled differentially [F(2.84) = 8.57. p< .001). Item Type Experiand the Newrnan-Keuls test revealed that each column rnent Group OP\" ~IPN OPI Mean ~IPI mean differed significantly from the other (p < .05). For 36 (12) 20 (10) II 53(13) 36 the DPN and MPN items, the usual superiority of DP was !'if 28 (12) 20 (10) 31 (12) 26 observed. When Ss paid more attention to the MP items l!'i 361L2) 27 (11) 51 (13) 38 because of isolation, the MP·DP effect was wiped out Mean 33 22 45 MPI items were recalled better than any other and the 34 ( 9) 19 ( 7) 68 ( 8) II 40 item. There is some indication that the three groups 2 !'II 26 ( 9) 27 ( 9) 4000) 31 differed in overall level of recall, with Group NI being 1l'i 40 l 9) 2S ( 8) 55 ( 9) 40 Mean 33 24 54 the least successful in erasing the MP·DP effect [F(2,42) = 2.57, p .10]. The Group by Item List items were shown visually via flash cards presented to the Type interaction [F(4,166) = 3.43, P < .005] is beat of a metronome. All items except the isolated ones were attributable to the lack of an MP-DP effect in Group NI. hand-lettered in black capital letters. The isolated ~lP items were The results of Experiment 3 with auditory isolation of hand-lettered in red capitals. For different groups. the first, second. or both presentations of three ~lP items were isolated MP items and Experiment 4 with auditory isolation of (Groups tx. :\1. and II. respectively). Fifteen college DP items appear in the third and final portions of undergraduates served in each group. Table I. respectively. The results resemble those found in Experiments I and 2. The fact that in Experiment 3 Experiment 2 the items were not recalled in a significantly different This study was the same as Experiment 1, except that three fashion (F < 1) might indicate that auditory isolation OP items rather than three ~lP items were isolated in red. There and auditory presentation were ineffective variables. were 30 high school students (Grade 11) in Groups II and IN, However. a glance at the results of Experiment 4 reveals and there were 26 Grade 11 students inGroup NI. the MP·DP effect and an enhancement of that effect when the DP items were isolated [F(254) = 9.33, Experiment 3 p < .001]. The trend in group differences in This experiment was conducted to replicate and extend the Experiments 3 and 4 parallels that found in the first two generality of Experiment 1. Everything was the same as in studies with overall recall lowest in Group NI, but in Experiment 1. except that auditory rather than visual presentation was used. Auditory presentation was via tape neither of the last two experiments were the group recorder with all but the isolated items read by a male. The differences reliable (Fs = 2.25 and 1.14), nor were the isolated ~IP items were read by a female whose voice was readily Group by Item Type interactions reliable (Fs < I). discriminable from the male voice. A different tape was prepared for Groups IN. NI. and II, There were 10 college undergraduates DISCUSSION in each group. Table I Mean Percent and SE x 100 (in Parentheses) Isolated (I) and Nonisolated (N) Items Recalled in Experiments 1-4

Experiment 4 This study was a replication of Experiment 2 using auditory rather than visual presentation, Auditory isolation of the OP items was effected as in Experiment 3, and there were 10 college undergraduates in each group.

RESULTS In none of the experiments were there any systematic effects due to list form or serial position; thus, combined recall scores are presented.

If one accepts Waugh's (1969) argument that isolated events receive more rehearsal than do nonisolated items. then interpretation of the present results seems straightforward. By isolating MP items, a situation is developed wherein Ss pay more attention to and rehearse MP events more so than when those items are not isolated. In fact, isolated MP items are recalled better than nonisolated DP items. Such results lend credence to the idea that MP·DP differences in recall are. in part, attributable to differences in the amount of rehearsal received by MP and DP items (D'Agostino &

ISOLATION OF PRACTICE ITEMS

DeRemer. 1972: Underwood. 1970). In addition, the data from Experiments 1 and 3 agree with the differential-rehearsal results reported by Rundus (1971) and Shaughnessy et al (1972). It would appear that the differential-rehearsal notion receives further support from the results of Experiments 2 and 4, which showed an increase in MP·DP differences in recall when the DP items were isolated. However, it is not at all clear why increased rehearsal via isolation should be somewhat more beneficial for DP than for MP items (i.e., auditory isolation was more salient in Experiment 4 than in Experiment 3, while the effectiveness of visual isolation was essentially the same for MP and DP items; seeTable 1). It is possible that the unique cues associated with isolation may provide additional stimuli for encoding, notwithstanding Waugh's (1969) formulation. If indeed such is the case, it also is unclear why the differential encoding provided by isolation should enhance DP item recall more than MP item recall (see D'Agostino & DeRemer, 1972). The fact that locus of isolation had only a marginal influence on recall is difficult to interpret. One might expect that I item recall would have been best in Group NI because of the extra attention paid to the second presentation. However, in three of the four experiments, I item recall was lowest in Group NI. Such a result might be more readily understandable if DPN

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recall was not also depressed in Group NI. It would appear that further examination of item isolation in MP-DP free recall studies is warranted. REFERENCES D'Agostino, P. R., & DeRemer, P. Item repetition in free and cued recall. Journal of Verbal Learning & Verbal Behavior, 1972,11,54-58. Elmes. D. G., Greener, W. I., & Wilkinson, W. C. Free recall of items presented after massed- and distributed-practice items. American Journal of Psychology, 1972,85,237-240. Melton, A. W. The situation with respect to the spacing of repetitions and memory. Journal of Verbal Learning & Verbal Behavior, 1970,9,596-606. Rundus, D. Analysis of rehearsal processes in free recall. Journal ofExperimental Psychology, 1971,89,63-77. Shaughnessy, J. 1., Zimmerman, J., & Underwood, B. J. Further evidence on the MP-DP effect in free-recall learning. Journal of Verbal Learning & Verbal Behavior, 1972, 11, 1-12. Thorndike, E. 1., & Lorge, I. The teacher's wordbook of 30,000 words. New York: Bureau of PUblications, Teachers College. Columbia University, 1944. - . Underwood, B. J. A breakdown of the total-time law in free-recall learning. Journal of Verbal Learning & Verbal Behavior, 1970,9,573-580. Waugh, N. C. Free recall of conspicuous items. Journal of Verbal Learning & Verbal Behavior, 1969,8,448-456. (Received for publication September 11, 1972; revision received November 9,1972)