Stephen R. Schmidt, Department of Psychology, Middle Tennessee State. University .... employed by Donaldson and Bass (1980). High-priority targets were.
Bulletin of the psychonomic Society 1990, 28 (2), 93-96
A test of resource-allocation explanations of the generation effect STEPHEN R. SCHMIDT Middle Tennessee State University, Murfreesboro, Tennessee Several current theories of the generation effect posit that generated items receive greater encoding resources than do read items in the same list. These theories were tested, by asking subjects to pay special attention to target items embedded in a list of background items. Targets were either read or generated, and received either normal or special attention. Background items were always read. Compared to memory for words in a list of read target and background items, memory for generated targets was enhanced and memory for surrounding read items was suppressed. These results paralleled the effects of the special attention instructions. It was suggested that generation is a controlled process requiring encoding resources that are taken from surrounding read items in a mixed-list design and from relational processing in a between-list design. When people are asked to generate missing material from a to-be-remembered word (e.g., ap_le), performance is enhanced on tests of explicit memory. Currently there are four prominent theories of this "generation effect": the displaced rehearsal hypothesis (Slamecka & Katsaiti, 1987), the inhibition hypothesis (Begg & Snider, 1987), the two-factor theory (Hirshman & Bjork, 1988), and the contextual theory (McDaniel, Waddill, & Einstein, 1988). Although there are many differences among these theories, each theory hypothesizes that generating some items in a list shifts resources away from the processing of intact items in the same list. In the research presented below, this assumption concerning expenditure of encoding resources is evaluated. We begin with a brief review of each theory, focusing on the form of the resourceallocation assumption and the evidence garnered in favor of the assumption. The supporting evidence was found to be open to numerous interpretations, and inconsistencies in the evidence were noted. An experiment that resolved these inconsistencies is then presented; it provided more convincing evidence for the resourceallocation assumption. Slamecka and Katsaiti (1987) provided the most convincing evidence for the encoding resource hypothesis. Subjects were asked to study semantically related word pairs, and comparisons between reading and generating were made both within and between subjects. In the within-subjects design, generated and intact items were mixed in the same list, and a typical generation effect was
found. However, no generation effect was found in the between-subjects design when one group of subjects read a list of words and a different group generated each word on the to-be-remembered list. In addition, memory for generated response terms was enhanced in the within-list design relative to memory for generated and read items in the between-list design. In contrast, memory for read response terms in the within-list design was suppressed relative to memory for read terms in the between-list design. Slamecka and Katsaiti (1987) argued that the generation effect in the within-list design was due to greater rehearsal of the generated items at the expense of the read items. To further support this hypothesis, using a withinlist design, Slamecka and Katsaiti asked subjects to rehearse word pairs only while they were in view: the generation effect disappeared. This led to the conclusion that the generation effect was the result of ' 'selective displaced rehearsal" of the generated items. Begg and Snider (1987) offered a somewhat different explanation for within-list generation effects. They found that memory for the read items in a mixed list was suppressed relative to a control list of read items. No difference was found between the generated items in the mixed list and the read items in the control list. Begg and Snider argued that the presence of generated items in a list led to inhibition of normal encoding of the read items in the list. Read items may only be processed to the level of identification, leading to a generalized, list-wide inhibition of read-item encoding. Hirshman and Bjork (1988) compared the effects of generation on free and cued recall in both within- and between-subjects designs. The generation effect was larger in cued than in free recall, and larger in within- than in between-subjects designs. In addition, these authors noted that the recall of read items was lower in their withinsubjects design (Experiment 4) than in their betweensubjects design (Experiment 1). In contrast, type of de-
I with to thank Elliot Hirshman, James Nairne, Constance R. Schmidt, and Norman J. Slamecka for their comments on an earlier report of this research. In addition, I wish to thank Kim Brockdorff, Julie Garver, David Gustavsen, Stephen Johnson, and Vincent Joven for their assistance in data collection and scoring. Requests for reprints should be sent to Stephen R. Schmidt, Department of Psychology, Middle Tennessee State University, Murfreesboro, TN 37132.
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sign had little effect on the recall of generated items. On the basis of these results, Hirshman and Bjork concluded that the size of the generation effect is exaggerated in within-subjects designs because the generated items compete with the intact items at encoding and retrieval. McDaniel et al. (1988) also focused on generation effects found in between-subjects designs. They varied the relation between the first and second terms in word pairs, the categorical structure of the list, and the type of memory test. McDaniel et al. demonstrated that generation enhanced individual-item processing of the generated term, enhanced processing of the relation between the words in related word pairs, and enhanced relational processing across items in a list, if such processing was congruent with the generation task. However, these effects of generation in between-subjects designs neither support nor preclude effects of generation on encoding resources in within-subjects designs. The preceding review suggests that three types of evidence support the assumption that generated items in a within-list design receive greater encoding resources than read items in the same list. First, the generation effect is larger in within- than in between-list designs (Hirshman & Bjork, 1988; Slamecka & Katsaiti, 1987). However, this finding is open to numerous interpretations. Perhaps the generation effect is the result of distinctiveness (Schmidt, 1988). Many effects of distinctiveness are found in within- but not in between-list designs (e.g., see Hunt & Elliot, 1980; McDaniel & Einstein, 1986). Alternatively, perhaps generated items in a mixed list have an advantage during retrieval. For example, generated items in a mixed list may be recalled first, so that generated items are subjected to less output interference than are intact items in the same list (Hirshman & Bjork, 1988). The second source of evidence comes from comparisons between the recall of read and generated items across mixed and unmixed lists. Slamecka & Katsaiti (1987) found enhanced recall of generated items and suppressed recall of read items when a mixed list was compared to an unmixed list. However, Begg and Snider (1987) and Hirshman and Bjork (1988) found only the suppressed recall of intact items, with no enhanced recall of generated items. The exact nature of these effects must be resolved before one can endorse any particular incarnation of the resource-allocation hypothesis. In addition, different emphasis on the retrieval (rather than encoding) of generated and intact items may also account for both the enhanced recall of generated items and/or the suppressed recall of read items in a mixed- relative to an unmixed-list design. The third source of evidence for differences in encoding resources in a mixed-list design is that controlled rehearsal can eliminate the generation effect in this design (Slamecka & Katsaiti, 1987). To interpret this result, we must assume that controlled rehearsal did not effect other processes that influence the generation effect. However,
several researchers have shown that requiring fixed overt rehearsal patterns changes the serial position curve in free recall (Fischler, Rundus, & Atkinson, 1970; Glanzer & Meinzer, 1967). Thus, controlled rehearsal does not mimic encoding processes in normal lists of intact items, and one should view results from this procedure as equivocal. Watkins and Sechler (1988) found a generation effect in within-subjects designs with an incidental learning task, a result some may interpret as evidence against the encoding-resource hypothesis. Presumably, neither generated nor read items receive any intentional rehearsal under these conditions, challenging the notion that generation effects in within-subjects designs result from selective rehearsal of generated items. However, even with incidental instructions, generated items may receive greater encoding resources than read items in the same list. Thus the Watkins and Sechler results challenge the selectiverehearsal hypothesis without damaging a more general encoding-resource hypothesis. In summary, evidence for the encoding-resource hypothesis is less than convincing. We subjected this hypothesis to further experimental testing in the experiment reported below. In a mixed-list design, we compared the generation effect with the effects of instructions to "pay special attention to" and "be sure to remember" several designated target items. Previous research has demonstrated that high-priority items are recognized (Schulz, 1971) and recalled (Tulving, 1969; Waugh, 1969) with a greater probability than are appropriate controls. In addition, memory for items immediately preceding and following high-priority items is suppressed (Schulz, 1971; Tulving, 1969; Waugh, 1969). Schulz (1971) specifically contrasted encoding and retrieval interpretations of the effects of priority instructions, and concluded that items surrounding high-priority events suffer a loss in effective presentation time. Thus, the apparent effects of priority instructions are equivalent to the hypothesized effects of generation in a mixed-list design. In the following experiment, six target items were randomly interspersed in a list of 30 background read items. In a 2 x 2 design, the target items were either read or generated, and were given either high or normal priority. If the generation effect is the result of increased encoding resources, then similar effects of high-priority instructions and generation should be found. In each case, target items should be remembered well, and items immediately preceding and following the targets should be poorly remembered. In addition, this design enables us to compare recall of items that are generated in a mixed list to recall of the same items when they are read in a list of read items. In previous research, this comparison revealed enhanced recall of the generated items (Slamecka & Katsaiti, 1987), and equivalent recall of read and generated items (Begg & Snider, 1987). Determining the true effect of generation on recall of read and generated items
GENERATION AND ATTENTION should provide a means of distinguishing between the alternative theories outlined above .
METHOD
Table 1 The Probability of Correct Recall and Clustering as a Function of the Target Item Priority, the Type of Item, and the Encoding Task Priority Item Type
Subjects and Design The subjects were 136 undergraduates who participated for extra credit. There were 17 subjects in each of eight groups . Two types of tasks performed on target items (read vs. generate) were crossed with two types of priority (normal vs. high) in a between-subjects design . This design was replicated with two different lists of words.
Target Background All nontarget items Items preceding targets
Materials The words, selected from the Thorndike and Lorge (1944) frequency norms, had frequencies between I and 10 per million and contained between four and eight letters. A sample of 72 words, judged as being of common orthography in part of an independent experiment (Schmidt, 1989), served as the stimuli . These words were randomly divided into two groups, and six items from each group were selected as targets. Eight lists were then constructed from these pools to create the 2 (task performed on the target: read vs. generate) x 2 (priority of target: high vs . normal) x 2 (word pool: I vs. 2) design . To-be-generated targets were printed with one internal letter replaced with a blank. In order to ensure correct completion of generated targets, the missing letter was printed to the right of each to-be-generated word. The subjects ' task was to fill in the provided letter. Similar generation tasks have been employed by Donaldson and Bass (1980). High-priority targets were designated by circling the items on the acquisition sheet. The target items always appeared in Serial Positions 9, II, 18, 22, 26, and 29 . These positions were randomly determined, with the restrictions that the items could not appear in the first or last six serial positions , and that targets did not appear consecutively .
Procedure All subjects were given intentional learning instructions. In addition , the subjects in the generation condition were instructed to fill in the missing letter in any words containing blanks. The subjects in the high-priority conditions were told . .. . . . you will notice that several of the words are circled. You are to pay particular attention to these words. Be extra sure to remember these high-priority words ... The acquisition list was presented on a single page, with the items listed in one column. The subjects were given a blank piece of paper, and asked to slide the paper down the page to expose each to-be-remembered item. A tape recorder sounded prerecorded tones at a 3-sec rate to signal the subjects when to go on to the next word. Following presentation, the subjects were asked to work on a word puzzle for 10 min. At the top of the puzzle, 32 eight-letter words were listed . The subjects' task was to find these words in an 18 x IS block of letters. No subject finished this task in the time provided. After the distractor task, the subjects were given 3 min to recall the words freely .
RESULTS Two separate analyses were conducted: one evaluating the probability of target- and background-item recall, and the second evaluating recall of preceding and following items. In the first analysis, background items included all nontargets in the list. In the second analysis, only the background items immediately preceding and following targets were included. The item in Serial Position 10 (a preceding and following item) was excluded from this analysis. A summary of target and background recall, and the recall of preceding and following items, is reported in Table 1. The traditional p value of < .05 was selected for all statistical tests. Each analysis is discussed below.
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Items following targets
Task
Normal
High
Read Generate
.15 .22
.24 .2S
Read Generate Read Generate Read Generate
. 17 . 16 . 15 .OS . 16 . 12
.13 .11 .05 .07 . 12 . 10
Target and Background Items
The probability of target recall (M = .22) exceeded the probability of background recall (M = . 14) [F(l , 128) = 30.32]. There was also a main effect of list [F(l, 128) = 5.55, MS. = .0215]. No other main effects were reliable. However, interactions were observed between item and task [F(l, 128) = 6.13] and between item and priority [F(l,128) = 14.61]. Generated targets were recalled better (M = .25) than were read targets (M = . 19) [t(67) = 2.74]. High-priority targets were recalled better (M =.26) than were normal-priority targets (M= .19) [t(67) = 3.45]. A small negative effect of generation on background-item recall was found, but this effect was not reliable [t(67) < 1.0]. Background items from lists containing high-priority targets were more poorly recalled (M = . 12) than were background items from normal-priority lists (M = .16) [t(67) = 1.95]. The MS. for each of these tests was .0144. The task and priority instructions did not combine to produce any interactions (Fs < 1.0).
Preceding and Following Items Preceding and following items were remembered better from normal-priority lists (M = .13) than from highpriority lists (M= .09) [F(I,128) = 5.43, MS. = .0198] . The main effect of task, in which reading led to greater recall of surrounding items (M = . 12) than did generating (M = .09), only approached significance [F = 2.69, P = . 10). However, detection of this effect may have been hampered by the low-level performance in the recall of items surrounding high-priority targets (see Table 1). Of prime theoretical importance, recall of items surrounding normal-priority generated targets (M = .10) was suppressed relative to normal-priority read targets (M = .15) [t(67) = 2.19]. Following items (M = .13) were remembered better than were preceding items (M = .09) [F(l,128) = 5.04, MS. = .0183] . The interactions between task and priority [F(1,128) = .97] were not significant.
DISCUSSION The results reported above provide direct evidence that the generation effect in a mixed-list design results in part from an increase in en-
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coding resources devoted to generated items at the expense of intact items. This support comes from two sources. First, the effects of generation and the effects of the priority instructions were remarkably similar. In each case, target recall was enhanced and recall of surrounding items was suppressed. Second, generating a target led to suppressed reca1l of items immediately surrounding the target. An alternative interpretation of the results reported above is that both generated and high-priority items received a retrieval advantage over intact items in the same list. However, this interpretation does not explain why the inhibitory effects of generation and priority instructions were focused on the items immediately preceding and following targets. These effects on surrounding items are most easily viewed as an encoding rather than a retrieval phenomenon (Schulz, 1971). In addition, the effects of both high priority (Schulz, 1971) and generation (Slamecka & Graf, 1978) are found in recognition. Any effects of priority operating during retrieval should be minimized on a recognition test, since subjects cannot control output order. A generation effect was found when memory for generated targets in the mixed list was compared to read targets in a homogeneous list. These results are not consistent with those reported by Begg and Snider (1987) and Hirshman and Bjork (1988), but they are consistent with the results of Slamecka and Katsaiti (1987) and Schmidt (1989) . Methodological differences across studies are undoubtedly responsible for these discrepancies. In contrast to procedures in typical memory experiments, Begg and Snider's (1987) subjects were required to make a recognition judgment of the cue on a cued recall test, prior to attempting to recall the target item. Hirshman and Bjork (1988) compared levels of recall across experiments differing in several respects. For example, they confounded a switch from a between- to a within-subjects manipulation of encoding task (read vs. generate) with a switch from a within- to a between-subjects manipulation of associative strength between words in related pairs (first vs. third associates). Generally, the results reported above do not distinguish between the various incarnations of the resource-allocation hypothesis. However, two kinds of evidence contradict the generalized inhibition hypothesis (Begg & Snider, 1987). First, as noted above, a generation effect was found in the comparison between generated items in a mixed list and read items in a homogeneous list. Second, generation led to suppressed recall of immediately surrounding items. On the basis of the generalized inhibition hypothesis, one would expect suppressed recall of most of the intact items in the list, inhibition of the intact items following the first generated item, or inhibition of the one or two intact items following each generated item. One would not predict the suppressed reca1l of items immediately preceding and following the generated targets . Perhaps the most parsimonious interpretation of the results reported above is that generated items receive greater rehearsal at the expense of read items (Slamecka & Katsaiti, 1987). The presentation of a generated item may interrupt rehearsal of the immediately preceding item, and rehearsa1 of the generated item may continue into the time period normally given to rehearsa1 of the following item. However, as noted above, the selective-rehearsal hypothesis cannot explain generation effects obtained in incidental tasks (Watkins & Sechler, 1988) or in between-subjects designs (McDaniel et aI., 1988). In addition, the results may be just as easily interpreted in terms of an increase in individualitem processing of generated items at the expense of surrounding read items (Hirshman & Bjork, 1988; Schmidt, 1989). If the generation effect results in part from a shift in resource allocation in a within-list design, why are generation effects occasionally found in between-list designs? A more complete explanation of the generation effect must rely on interactions between list structure, types of information encoded, and the nature of the memory test (McDaniel et aI., 1988). In a between-subjects design, generation appears to increase individual-item processing at the expense of whole-list organization (Schmidt & Cherry, 1989). On memory tests in which list organization is important (e .g., free recall), the increased individual-item processing and decreased relational processing may lead to no net effect of generation (Slamecka and Katsaiti, 1987), or to a negative generation effect (Schmidt & Cherry, 1989). In contrast, on recognition (Schmidt &
Cherry, 1989; Slamecka and Graf, 1978) or cued recall tests (Hirshman & Bjork, 1988; McDaniel et aI., 1988), list organization is less important, and positive effects of generation are found even in betweenlist designs. In conclusion, we tested the hypothesis that generation effects found in mixed-list designs result in part from an increase in encoding resources allocated to generated items at the expense of resources allocated to intact items. Previous research provided only weak support for this conclusion. The results presented above demonstrated specific tradeoffs between the reca1l of generated and intact items in the same list, suppressed recall of items immediately surrounding generated items, and parallel effects of generation and priority instructions. The best explanation of these results is that generation increaSes individual-item processing of the generated items at the expense of surrounding intact items. REFERENCES BEGG, I., " SNIDER, A. (1987) . The generation effect: Evidence for generalized inhibition. Journal of Experimental Psychology: Learning, Memory, & Cognition , 13, 553-563. DoNALDSON, W., " BASS, M. (1980). Relational information and memory for problem solutions. Journal of Verbal Learning & Verbal Behavior, 19, 26-35 . FISCHLER,I., RUNDUS, D. ,,, ATKINSON, R. C. (1970) . Effects of overt rehearsal procedures on free reca1l. Psychonomic Science, 19,249-250. GLANZER, M., " MEINZER, A. (1967). The effects of intra-list activity on free recall. Journal of Verbal Learning & Verbal Behavior, 6, 928-935. HIRSHMAN, E ., ,, BJORK, R. A. (1988). The generation effect: Support for a two-factor theory. Journal of Experimental Psychology: Learning, Memory, & Cognition, 14, 484-494. HUNT, R. R ., " ELUOT, J. M. (1980). The role of nonsemantic information in memory: Orthographic distinctiveness effects on retention . Journal of Experimental Psychology: General, 109, 49-74. McDANIEL, M. A., "EINSTEIN, O . O . (1986) . Bizarre imagery as an effective memory aid: The importance of distinctiveness . Journal of Experimental Psycholcgy: Leaming, Memory, & Cognition, 12,54-65. McDANIEL, M. A., WADDILL, P. J.," EINSTEIN, O . O. (1988) . A contextual account of the generation effect: A three-factor theory. Journal of Memory & Language, 27, 521-536. ScHMIDT, S . R . (1988 , April). Is generation a type of distinctiveness? Paper presentation at the annual meeting of the Midwestern Psychology Association , Chicago. ScHMIDT, S. R. (1989). A distinctive procedures account of the generation effect. Manuscript submitted for publication. ScHMIDT, S. R., " CHERRY, K. (1989). The negative generation effect: Delineation of a phenomenon. Memory & Cognition, 17, 359-369. ScHULZ, L. S. (1971) . Effects of high-priority events on reca1l and recognition of other events. Journal of Verbal Learning & Verbal Behavior, 10, 322-330. SLAMECKA, N. J .," OKAF, P. (1978). The generation effect: Delineation of a phenomenon. Journal of Experimental Psychology: Human Learning & Memory, 4, 592-604. SLAMECKA, N. J., "KATSAITI, L. T . (1987). The generation effect as an artifact of selective displaced rehearsa1. Journal of Memory & Language, 26, 589-607. THORNDIKE , E. L., " LoRGE, I. (1944). The teacher's word book of 30,000 words. New York: Teachers College Press, Columbia University . TULVING, E. (1969). Retrograde amnesia in free recall. Science, 164, 88-90. WATKINS, M. J.," SECHLER, E . S. (1988). Generation effect with an incidental memorization procedure. Journal of Memory & Language, 27, 537-544. WAUGH, N. C. (1969). Free recall of conspicuous items. Journal of Verbal Learning & Verbal Behavior, 8, 448-456. (Manuscript received July 20, 1989.)
