MARK A. McDANIEL. Purdue University, West Lafayette, Indiana and. GILLES O. EINSTEIN and TERESA LOLLIS. Furman University, Greenville, South Carolina.
Memory & Cognition 1988, 16 (1), 8-14
Qualitative and quantitative considerations in encoding difficulty effects MARK A. McDANIEL Purdue University, West Lafayette, Indiana and GILLES O. EINSTEIN and TERESA LOLLIS Furman University, Greenville, South Carolina We hypothesized that the effects of encoding difficulty on the memorability of verbal material would depend on both the type of processing induced by the difficulty manipulation and the type of processing afforded by the material. We predicted that if the processing induced by encoding difficulty were complementary to the processing afforded by the material, then difficulty would enhance recall more so than if the processing induced by the two sources were redundant. These expectations were tested by requiring subjects to process either a structured or an unstructured word list with either a sorting task or a pleasantness rating task; the difficulty of each orienting task was also manipulated. We assumed that sorting and pleasantness rating required primarily relational and individual-item processing, respectively, and that the structured and unstructured word lists afforded relational and individual-item processing, respectively. These assumptions were supported by clustering in free recall and by recognition performance. The primary finding was that difficult sorting increased recall only for the unrelated list, whereas difficult pleasantness judgments increased recall most robustly for the related list. These results support the present framework and help illuminate the boundary conditions of the "difficulty effect." 1984; McDaniel, Einstein, Dunay, & Cobb, 1986; Zacks, Hasher, Sanft, & Rose, 1983). For example, Zacks et al. (1983), in five experiments, manipulated the difficulty of performing several different orienting tasks (anagram solving, sentence completion, and picture naming). Increased difficulty did not improve recall of target words with any of these tasks. Einstein et al. (1984) increased the difficulty of processing a fairy tale by either scrambling the order of the sentences or by deleting some of the letters in each word of the text. Both manipulations produced substantial increases in processing time over that required for an intact control text, but only the letter deletion manipulation produced increased recall. As outlined above, difficulty manipulations appear to produce increases in memory in some situations but not in others. Recently, we suggested an initial explanation of these disparate results based on consideration of the type of processing induced by different difficulty manipulations in conjunction with the type of processing invited by the material itself (Einstein et al., 1984; McDaniel et al., 1986). Our framework focuses on three components of the encoding situation: the type of processing induced by the manipulations of difficulty or effort, the type of processing invited by the stimulus material itself, and the overlap between the processing associated with each of these sources. We propose that increases in encoding difficulty or effort will improve memory if the type of processing required by the difficulty manipulation is appropriate for the retrieval task and if this type of process-
In the past decade, a number of studies have suggested a positive relationship between the difficulty or effort that is required to encode an item and the memory for that item (Auble & Franks, 1978; Einstein, 1976; Ellis, Thomas, & Rodriguez, 1984; Jacoby, 1978; Kolers, 1973; McDaniel, 1981; O'Brien & Myers, 1985; Tyler, Hertel, McCallum, & Ellis, 1979). For example, Jacoby (1978) found that filling in missing letters of words produces higher recall than does reading intact versions of words. Tyler et al. (1979) examined the effects oflow and high effort manipulations with anagram and sentence completion tasks, and with both tasks they found that' 'high effort led to better recall than low effort" (p. 607). As another example, McDaniel (1981) found that "selfembedded sentences that were more difficult to process were better remembered than ... more easily processed sentences" (p. 494). Several recent studies, however, seriously question the relation between encoding difficulty and memory (Einstein, McDaniel, Bowers, & Stevens, Preparation of this article was supported in part by the National Institute of Child Health and Human Development Grant HD 23984 awarded to the first two authors. The first two authors contributed equally to this project; consequently, their order of authorship was determined arbitrarily. We appreciate Scott Maxwell's valuable assistance in evaluating the analysis of covariance results and J. Scott Lackey's help in analyzing other results. This research was reported in part at the Midwestern Psychological Association Annual Meeting, Chicago, May 1986. Address reprint requests to Mark McDaniel, Department of Psychological Sciences, Purdue University, West Lafayette, IN 47907.
Copyright 1987 Psychonomic Society, Inc.
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ENCODING DIFFICULTY AND MEMORY ing is not sufficiently induced by the stimulus itself. For recall, our framework embraces the view that good memory is dependent on the combined influences of two types of information: relational and individual-item information (Einstein & Hunt, 1980; Hunt & Einstein, 1981; Hunt & Seta, 1984; see also Graf, 1982, and G. Mandler, 1979, for similar views). Thus, in general, difficulty manipulations that encourage the encoding of relational and/or individual-item processing are expected to support good recall. However, the relative effectiveness of such difficulty manipulations is expected to be inversely related to the degree to which the encoding of these two types of information is invited by the material itself. We label this the material appropriate difjiculty (MAD) framework. There is some preliminary support for the MAD framework in the domain of prose recall. McDaniel et al. (1986) had subjects read fairy tales (material presumed to invite relational processing) or unstructured narrative passages (material presumed to invite individual-item processing). Some of the subjects were given a passage with missing letters and told to fill in the blanks; this task presumably encouraged the encoding of individual-item information. Other subjects received a scrambled version of the story and were instructed to put the sentences into proper order; this task was assumed to promote relational processing. Although both tasks increased processing difficulty, the two tasks did not produce equal increments in recall performance. As predicted by our framework, the letter deletion task produced better recall (compared with reading an intact version of the text) only when performed on the fairy tales. By contrast, sentence unscrambling produced better recall (compared with reading an intact text) primarily when performed on the unstructured narratives. Thus, difficulty manipulations benefited recall when they encouraged the encoding of nonredundant information, that is, information that was not encoded obligatorily from the material itself. In the present experiment we applied the MAD framework to memory for word lists. This allowed us to test the generality of our framework, and provided a test of our framework using materials that are predominant in the encoding difficulty literature, thus making the present research comparable to the existing literature on encoding difficulty and memory. Moreover, the word list memory domain afforded us an opportunity to collect supplementary measures (e.g., clustering and recognition) that allowed us to gauge the extent to which our difficulty manipulations induced relational versus individual-item processing. One other feature of the present experiment deserves mention. In addition to manipulating the type of difficulty task (relational, individual-item) and the type of materials (structured, unstructured), we orthogonally varied the amount of difficulty induced by the encoding tasks (simple, difficult). In our previous experiments with prose materials (Einstein et al., 1984; McDaniel et al., 1986), only the first two factors were varied. The results of these studies produced a significant interaction between type of difficulty task and type of mateials, thereby in-
9
dicating that certain difficulty tasks improve memory only for certain types of learning materials. As such, these results demonstrated the importance of qualitative considerations in predicting the appropriateness or effectiveness of a given difficulty manipulation. They did not, however, address the question of whether or not quantitative factors are also important: that is, given that an encoding task is appropriate, will a difficult level of that task produce higher recall than will a simple level of that task? Rather than focusing strictly on qualitative factors associated with difficulty, the design of the present experiment allowed us to test both quantitative and qualitative effects of difficulty. The subjects performed either simple or difficult orienting tasks that encouraged the encoding either of relational information (sorting items into categories) or of individualitem information (making pleasantness decisions). Furthermore, these activities were performed on either highly related or unrelated lists of words. Related word lists have been shown to invite the encoding of relational information, and unrelated word lists appear to invite the encoding of item-specific information (Einstein & Hunt, 1980; Hunt & Einstein, 1981). We derived the following predictions from our framework. For the related word list, increases in individual-item difficulty (pleasantness rating task) should produce enhanced recall, but increases in relational difficulty (sorting task) should have minimal effect on recall. This prediction follows from the assumption that individual-item processing is complementary to the relational processing afforded by a related word list but that relational processing is redundant with the processing invited by the related word list (see Einstein & Hunt, 1980). Extending this line of reasoning to the unrelated word list (which encourages individual-item processing; Einstein & Hunt, 1980), increases in relational difficulty (sorting task) should produce robust increases in recall, but increases in individual-item difficulty (pleasantness rating task) should produce little or no increase in recall. Thus, according to the MAD framework, a higher order interaction between difficulty, list type, and encoding task is expected for recall. Moreover, ancillary recognition and clustering measures should differentially vary as a function of the type of task peformed. Assuming that recognition is enhanced primarily by individual-item processing and that clustering in free recall is enhanced primarily by relational processing (Einstein & Hunt, 1980), then the pleasantness rating task should primarily enhance recognition and the sorting task should mainly affect clustering. Theoretical positions that do not consider the appropriateness of the difficulty task for the learning material make different predictions. For example, the general notion that increased encoding effort or difficulty promotes better retention (e.g., Krinsky & Nelson, 1981; Tyler et al., 1979) predicts a main effect of task difficulty (such that difficulty increases recall and perhaps recognition) not accompanied by higher order interactions. A more empirical approach suggesting that some effort manipulations
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McDANIEL, EINSTEIN, AND LOLLIS
are effective (e.g., manipulations requiring generation of the target) and others are not (Zacks et aI., 1983) could accommodate the possibility that one or both difficulty manipulations would fail to improve recall, but such a failure should be consistently observed. That is, this approach also would not expect difficulty to interact with list type.
prehension of the story. Subjects were then given a 5-min free recall test, which was followed by an untimed recognition test. Separate recognition tests were created for the related and unrelated lists. Each test contained 30 target items and 30 distractors. Five new items from each of the six categories in the learning list were used as distractors. Subjects were asked to make an "old/new" decision for each item.
RESULTS
METHOD Subjects Subjects were 96 Furman University introductory psychology students who received course credit for their participation. They were tested in groups ranging from 1 to 4 students. Design and Materials The design was a 2 x2 x2 factorial with list structure (related words, unrelated words), orienting task (sorting cards, pleasantness rating), and level of difficulty of the orienting task (easy, difficult) as the variables. All variables were manipulated between subjects, and 12 subjects were assigned to each of the eight conditions. Each of the two word lists contained 30 familiar nouns. The related word list contained 5 words from each of six taxonomic categories (parts of the body, articles of clothing, animals, insects, fruits, and musical instruments) that were known to be highly salient to college students (Einstein & Hunt, 1980). The words from each category were selected from the Battig and Montague (1969) category norms. The unrelated word list contained 5 words from each of six categories (things that are green, liquids, things that make noise, things made of wood, things that fly, and things that women wear) that were not readily apparent to college subjects (Einstein & Hunt, 1980). For both the sorting and pleasantness rating tasks, the word list was presented on a deck of 303 x 5 in. unlined index cards, with one list item typed in the center of each card. The list items were randomly arranged with the constraint that no items from the same category were adjacent. Procedure To maintain an incidentalleaming situation, we told subjects that the purpose of the experiment was to investigate their judgment of certain word characteristics. They were presented with appropriate materials and given instructions relevant to their conditions. Subjects in the simple sorting condition were given a large cardboard sheet with the categories appropriate to their list printed on it and were instructed to place each item in the card deck under its appropriate category label. Subjects in the difficult sorting condition were given a large cardboard sheet with six letters printed on it. Although the letters corresponded to the first letter of each group heading, the subjects were not aware of this fact and had to decide for themselves the nature of the category that they wanted the letter to represent. In both the simple and difficult sorting tasks, subjects were required to sort each item as it was presented. Once an item was sorted, subjects were not allowed to re-sort that item. Subjects in the simple pleasantness conditions were instructed to rate whether each word's meaning was more or less pleasant than the word mayor. If it was more pleasant than the word mayor, they were to write M on an answer sheet; if it was less pleasant than the word mayor, they were to write an L. Subjects in the difficult pleasantness rating conditions rated the degree to which each word was more or less pleasant than the word mayor on a scale from o to 100, with the word mayor assigned a pleasantness value of 50. After making a decision, they recorded the response on an answer sheet. The amount of time each subject needed to complete the orienting task was recorded. After completing the orienting task, subjects were asked to read a story for I min and to rate their com-
Processing Time For all statistical analyses, the rejection level was set at .05. A three-factor between-subjects analysis of variance (ANOYA) performed on the processing times indicated that the difficult tasks took more time to complete than the easy tasks [F(1,88) = 95.44, MSe = 12,154.53] (see Table I for the means). Thus, the processing times confirm that the difficulty manipulations were effective in increasing the difficulty required to perform a particular orienting task. There was also a significant main effect of list type, with the unrelated list taking more time to process than the related list [F(I,88) = 43.48]. All of the two-way interactions were significant. The differences in processing time between difficult and simple tasks were more pronounced for the unrelated than for the related list [F(1,88) = 27.33] and were more pronounced for the sorting task than for the pleasantness rating task [F(1,88) = 8.27]. Also the processing times for the pleasantness rating task were slightly longer with the unrelated list than with the related list, but for the sorting task processing times were substantially longer for the unrelated list than for the related list [F(1,88) = 29.96]. Finally, there was a significant three-way interaction [F(I,88) = 20.58]. For present purposes, this interaction is best interpreted in terms of how the effects of difficulty varied across orienting task and word list. Making the pleasantness rating task more difficult increased processing time to a similar degree for both word lists (average increase of 170.7 and 139.6 sec for the unrelated and related lists, respectively), but making the sorting task more difficult increased processing time much more markedly for the unrelated list than for the related list (an average increase of 504.3 and 64.9 sec for the unrelated and related lists, respectively).
Recall Table 2 displays the average number of words recalled as a function of type of orienting task, task difficulty, and type of word list. A three-factor between-subjects ANOYA of these data indicated that in general the difficult tasks Table 1 Mean Processing Times (in sec) as a Function of Orienting Task, Task Difficulty, and Word List Task Type Sorting Pleasantness List Type Related Unrelated
Simple 149.3 159.0
Difficult 288.9 329.7
Simple 105.2 157.1
Difficult 170.1 66\.4
ENCODING DIFFICULTY AND MEMORY Table 2 Mean Number of Items Recalled and Clustering Scores as a Function of Orienting Task, Task Difficulty, and Word List Task Type Sorting
Pleasantness List Type Related Recall Adjusted Recall* Clustering Unrelated Recall Adjusted Recall Clustering
Simple
Difficult
16.4 16.7 .46
2\.4 21.3 .52
19.0 19.4 .65
17.5 17.7 .71
11.4 1\.6 - .01
14.1 13.9 .05
16.4 16.6 .48
23.7 22.7 .67
*Recall adjusted according to the analysis of covariance with processing time as the covariate.
significantly improved recall relative to the simple tasks [F(1,88) = 30.22, MSe = 8.94]. Also, the related list was recalled significantly better than the unrelated list [F(1,88) = 12.85], and the sorting task produced significantly better recall than the pleasantness rating task [F(1,88) = 29.48]. These main effects were qualified by significant interactions. Difficulty significantly interacted with list type such that the difficult tasks produced more improvement in recall (relative to the simple tasks) for the unrelated than for the related list [F(1,88) = 6.91]. List type also interacted with type of orienting task such that both orienting tasks produced equivalent recall on the related list but that sorting produced higher recall than pleasantness rating on the unrelated list [F(1,88) = 42.53]. Most important, the three-way interaction between type of orienting task, task difficulty, and type of word list was significant [F(1,88) = 20.62]. This interaction revealed that the effects of task difficulty were dependent on task type and list type. Difficult sorting improved recall relative to simple sorting for the unrelated word list [F( 1,88) = 35.30] but not for the related list (average recall was nominally lower for the difficult sorting task in this case). On the other hand, difficult pleasantness rating improved recall relative to simple pleasantness rating for the related list more so than for the unrelated list. Average increase in recall as a function of difficulty was 5.0 and 2.7 words for the related and unrelated lists, respectively; both were significant increases [F(1,88) = 16.79, and F(1,88) = 4.95]. Although the processing time results did not perfectly parallel the recall results, there was enough similarity to suggest an interpretation of recall in terms of total processing time. To examine this possibility, we performed an analysis of covariance (ANCOVA) on the recall data with processing time as the covariate. Processing time was significantly associated with recall [F(1,87) = 42.! 1, MSe = 8.97]. With the influence of processing time partialed out, the main effect of difficulty on recall was no longer significant [F(1,87) = 1.02], and the difficulty x list interaction also was no longer significant [F(1,87) = 1.27]. It should be noted, however, that the absence of effects may not be due entirely to the processing time
II
covariate per se because of collinearity problems introduced by the ANCOVA procedure.' More important for present purposes, the three-way interaction remained significant [F(1,87) = 13.85], suggesting that the complex interaction between difficulty, orienting task, and word lists cannot be accounted for by processing time. Moreover, when the recall means were adjusted for processing time (see Table 2), the mnemonic advantage for difficult over simple sorting for the unrelated list (adjusted mean difference = 6.05) and the advantage for difficult over simple pleasantness rating for the related list (adjusted mean difference = 4.67) remained significant [F(1,87) = 24.46, and F(1,87) = 14.57 , respectively]. The advantage for difficult over simple pleasantness rating for the unrelated list (adjusted mean difference = 2.30) was no longer significant, however [F(1,87) = 3.42]. The other significant effects in the ANOVA that pertained to type of orienting task or type of word list remained significant in the ANCOVA. Roenker, Thompson, and Brown's (1971) adjusted ratio of clustering score was used to measure category clustering in recall. This score ranges from 1.0 to -1.0, with a score of 1.0 indicating perfect clustering and 0 indicating chance clustering. An ANOVA of the clustering scores (see Table 2 for the means) indicated that clustering was significantly higher for the related list than for the unrelated list [F(l,88) = 33.49, MSe = .06] and that clustering was higher for the sorting task than for the pleasantness task [F(1,88) = 55.32]. List type and type of orienting task interacted such that the enhancement in clustering due to sorting (relative to pleasantness rating) was especially robust for the unrelated list [F(1,88) = 13.10]. This was so because clustering was especially poor (at chance levels) when the unrelated list, but not the related list, was rated for pleasantness. These effects are consistent with the assumptions that both related word lists and sorting tasks encourage relational processing. No other significant effects emerged, although the difficult tasks tended to produce more clustering than did the simple tasks [F(1,88) = 3.74, P < .06]. Planned comparisons indicated that difficulty enhanced clustering only for the sorting task performed on the unrelated list [F(1,88) = 3.67, P < .06 (Fs < 1 for sorting and pleasantness tasks performed on the related list and for the pleasantness task performed on the unrelated list)]. Recognition As shown in Table 3, the recognition data were tabulated for d' scores.i hits, and false alarms. Each ofthese measures was analyzed with a three-factor betweensubjects ANOV A. The d' scores were significantly higher for the unrelated than for the related list [F(1,88) = 36.89, MSe = .28], and d' scores were significantly higher after pleasantness rating than after sorting [F(1,88) = 41.47]. These two factors interacted such that d' scores were notably lower in the condition in which the related list was sorted than in the other three conditions [F(1,88) = 10.821. Put another way, pleasantness rating enhanced
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McDANIEL, EINSTEIN, AND LOLLIS Table 3 Mean d' Scores,2 Hits, and False Alarms as a Function of Orienting Task, Task Difficulty, and Type of Word List Task Type Pleasantness
List Type Related d' Hits False Alarms Unrelated d' Hits False Alarms
Sorting
Easy
Difficult
Easy
Difficult
3.44 27.9 .8
3.73 29.2 .7
2.52 25.8 2.9
2.54 26.3 3.5
3.72 29.2 .8
4.05 29.8 .2
3.23 27.5 1.4
3.86 29.3 .4
recognition more than sorting did primarily for the related list. These results are consistent with the assumptions that both unrelated word lists and pleasantness rating tasks encourage individual-item processing. Difficult tasks produced higher d' scores than did simple tasks [F(1,88) = 8.64]. Analyses of hits and false alarms generally revealed that the effects obtained for the d' measure were due to differences in both hits and false alarms. Hits were higher and false alarms were lower for the unrelated list than for the related list [F(l,88) = 18.44, MSe = 3.71 for hits, and F(l,88) = 17.94, MSe = 2.09 forfalse alarms]. Hits were also significantly higher and false alarms significantly lower for pleasantness rating than for sorting [F(l,88) = 21.28 for hits, and F(l,88) = 24.41 for false alarms]. Furthermore, the pleasantness rating task increased hits [F(l,88) = 20.90] and lowered false alarms [F(1,88) = 35.87] mainly for the related word list. Pleasantness rating produced neither significantly more hits [F(l,88) = 2.77] nor fewer false alarms [F( 1,88) = 1. 1] for the unrelated list. The only comparison that varied among the three recognition measures was that difficult tasks increased hits [F(l,88) = 7.31] but had no effect on false alarms (F < 1). A result that was consistently found with all three recognition measures was that the unrelated list produced better recognition performance than did the related list. This result supports our assumption that unrelated lists typically invite more individual-item processing than do related lists. An alternative interpretation suggested by the editor of this journal, however, is that the two word lists may have differed on some important normative dimension, such as familiarity or frequency. To examine this possibility, we first used the Toglia and Battig (l978) word norms to compare the lists in terms of concreteness, meaningfulness, familiarity, and pleasantness. Twentytwo of the words from the related list and 16 of the words from the unrelated list were listed in the Toglia and Battig norms. Words in these norms are scored on a 7-point scale, with 1 representing low on a dimension and 7 representing high on a dimension. The mean ratings for the related list on the dimensions of concreteness, mean-
°
ingfulness, familiarity, and pleasantness were 6.07, 4.56, 6.09, and 4.57, respectively. The corresponding mean ratings for the unrelated list were 5.91,4.43,6.10, and 4.83. We performed separate F tests to compare the related and unrelated lists on each of the four dimensions. These tests revealed that the normed items from the two word lists did not differ reliably on concreteness [F(l,36) = 3.51, MSe = .07], meaningfulness [F(l,36) = 1.25, MSe = .18], familiarity (F < 1, MSe = .12), or pleasantness [F(l,36) = 1.21, MSe = .51]. Next we used the Kucera and Francis (l967) norms to compare the lists in terms of word frequency. Twenty-seven words from each list were in the Kucera and Francis norms (termite, giraffe, and trombone from the related list were not included, and trombone, lettuce, and hairband from the unrelated list were not included). Frequency values from these norms represent the absolute frequency of occurrence of a word in a 1,014,232-word corpus of natural-language text. The mean frequencies for the related list and the unrelated list were 21.26 and 17.85, respectively. This difference was not significant (F < 1, MSe = 907.63). Thus, it appears unlikely that the words in our two lists differed along attributes related to recognition memory. Still, because performance was at ceiling, especially for the pleasantness rating tasks, the recognition findings should be viewed cautiously. DISCUSSION The present results converge with other recent findings (e.g., Einstein et al., 1984; Ellis et al., 1984; McDaniel et al., 1986; Zackset al., 1983) to indicate that increases in task difficulty do not invariably produce better recall performance. In the present experiment, the effects of encoding difficulty interacted in a complex fashion with the type of encoding task and the type of word list. This pattern was not anticipated by extant theoretical notions regarding the mnemonic benefits of encoding difficulty. One view (Krinsky & Nelson, 1981; see also Tyler et al., 1979) holds that increasing task difficulty or effort increases memory performance, another view (Zacks et al., 1983) makes a general distinction between more potent difficulty manipulations (e.g., tasks requiring generation) and less potent difficulty manipulations (e.g., increasing anagram difficulty), and a third notion (Jacoby, Craik, & Begg, 1979) is that the processing associated with increased difficulty produces a more distinctive encoding. (According to this third notion, memory peformance will depend on the degree to which the retrieval task depends on the distinctiveness of the memory record.) According to these views, if a difficult task is found to enhance memory, then it should do so in general (as long as the retrieval task is not varied), regardless of variations in the particular word list to which the orienting task is applied. An account based on processing time is also not fully supported: When the variance accounted for by
ENCODING DIFFICULTY AND MEMORY processing time was partialed out, the critical three-way interaction (between difficulty, list type, and encoding task) remained highly significant. For the most part, the pattern of results including the results of the clustering and recognition scores was predicted by the MAD framework. Applied to the present results, the idea is that unrelated lists and pleasantness rating tasks encourage the processing of individual-item information, and related lists and sorting tasks encourage the processing of relational information. (These claims are associated with the findings that recognition was higher for the unrelated list and for the pleasantness rating task, but that clustering was higher for the related list and for the sorting task.) Thus, performing sorting on a related word list should produce impoverished individualitem processing, an expectation consistent with the finding that recognition performance was lowest when the related word list was sorted. Also, rating the pleasantness of unrelated list items should produce impoverished relational processing; this expectation is supported by the finding that clustering performance was lowest and at chance levels when pleasantness rating was performed on the unrelated list. Note also that clustering did not increase proportionally when relational processing was stimulated by both the sorting task and the related list relative to when it was stimulated by only one or the other (as indicated by a two-way interaction in clustering between processing task and list type). Similarly, when the unrelated word list was rated for pleasantness, recognition did not improve proportionally, as indicated by the significant twoway interaction between task type and list type. This finding highlights an important point with regard to understanding the obtained difficulty effects: increasing redundant processing has increasingly smaller benefits. The effects of increasing the difficulty of the sorting and pleasantness rating tasks are directly associated with the above observations. The specific impoverishment in the particular processing task/list type combinations enumerated above would not be remedied simply by increasing the difficulty of the task. In these cases, difficulty presumably would result in additional processing of the type already induced by the task and the material, and, as suggested above, redundant processing has proportionally decreased benefits. Consequently, increased difficulty in these instances had very little, if any, effect on recall. Difficulty significantly enhanced recall levels only when it induced processing that was complementary to the processing invited by the material itself. It should be noted that we cannot be certain that the increase in difficulty for the two orienting tasks was equivalent or even that the baseline degree of processing induced by our simple tasks was equivalent. In fact, the absence of a task type (sorting, pleasantness rating) X list type interaction for the simple tasks (simple sorting produced nominally better recall than did simple pleasantness rating, regardless oflist type) may indicate that these simple tasks differed on more than only a qualitative dimension. Nevertheless, the major point remains that increasing the difficulty of
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these tasks increased recall primarily when the task was appropriate for the particular word list. Thus, the present results stand as the first demonstration of the importance of both qualitative and quantitative factors for understanding the effects of difficulty on memory. Einstein et al. (1984) and McDaniel et al. (1986) previously demonstrated that the mnemonic effectiveness of different types of difficulty manipulations depends on the nature of the learning materials. Others (e.g., Jacoby, 1978; Tyler et al., 1979) have shown that more difficult tasks produce better memory than do simple tasks when the nature of the difficulty manipulations is held constant. The present results capture both of the above notions. To account for why material-appropriate difficulty improves recall, we assume that the increased processing and/or effort necessitated by the difficulty manipulation is reflected in the information incorporated into the memory trace. In the present context, the idea is that the sorting difficulty manipulation promotes the encoding of more extensive interitem associations and/or organizational schemas and that the pleasantness rating difficulty manipulation encourages the encoding of more extensive descriptions (Graf, 1982) of individual list items. Furthermore, our view is that both types of information are important for recall, and these serve different but complementary functions at retrieval (Einstein et al., 1984; Hunt & Einstein, 1981; Hunt & Marschark, 1987; Hunt & Seta, 1984). Relational or organizational information is thought to be useful in directing retrieval (1. M. Mandler, 1979) or specifying a search set, whereas individualitem information helps discriminate among possible class members to allow precise identification of the word event (see Hunt & Marschark, 1987, for more extensive discussion of the roles of these two types of information at retrieval) . Our fmdings and approach may be useful in understanding other reported results. Zacks et al. (1983) employed an anagram task to manipulate encoding difficulty (Experiments Ia and lb) of an unrelated word list (Zacks, personal communication, August 8, 1984). The anagram task would seem to encourage individual-item processing, and the unrelated list would also serve to encourage individual-item processing; therefore, increasing anagram difficulty should not improve free recall. In line with this expectation, Zacks et al. (1983) reported no effects due to the difficulty manipulation. Krinsky and Nelson (1981) also manipulated encoding difficulty for a list of unrelated words but found significant improvement in free recall due to difficulty. By our formulation, one would expect that Krinsky and Nelson's (1981) difficulty manipulation encouraged some relational processing. Their difficult semantic task involved asking subjects to respond to the question "Does the word represent something that is manmade, too large to be carried in a pocket, and could be used as a weapon?" (p. 294), whereas the easy semantic task was the question "Does the word represent something you could hold in your hand?" (p. 294). The difficult question would encourage subjects to attend to more
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McDANIEL, EINSTEIN, AND LOLLIS
attributes of the item represented by each word, thus providing several dimensions around which seemingly unrelated words might be organized. Unfortunately, Krinsky and Nelson did not report the clustering measures needed to support this interpretation. Finally, in addition to its contributions to the basic research arena, our framework has some practical implications. Norman (1978) proposed that guided confusion may be a useful pedagogical device because it creates more active, semantic processing of the to-be-learned material. Assuming that confusion and difficulty may overlap conceptually, our results suggest that both the type of confusion and the type of material will be important in determining whether guided confusion improves learning. Organized material should benefit most from confusion that induces individual-item processing, whereas relatively unstructured material should most benefit from confusion that induces relational processing. REFERENCES AUBLE, P. M., & FRANKS, 1. J. (1978). The effects of effort toward comprehension on recall. Memory & Cognition, 6, 20-25. BATTIG, W. F., & MONTAGUE, W. E. (1969). Category norms for verbal items in 56 categories: A replication and extension of the Connecticut category norms. Journal ofExperimentalPsychologyMonographs, 80(3, Pt. 2). EINSTEIN, G. O. (1976). Effects of simultaneous interference upon free recall learning and retention. Memory & Cognition, 4, 701-708. EINSTEIN, G. 0., & HUNT, R. R. (1980). Levels of processing and organization: Additive effects of individual-item and relational processing. Journal ofExperimentalPsychology:Human Learning & Memory, 6, 588-598. EINSTEIN, G. 0., McDANIEL, M. A., BoWERS, C. A., & STEVENS, D. T. (1984). Memory for prose: The influence of relational and propositionspecific processing. Journal ofExperimental Psychology: Learning, Memory, & Cognition, 10, 133-143. ELLIS, H. c., THOMAS, R. L., & RODRIGUEZ, I. A. (1984). Emotional mood states and memory: Elaborative encoding, semantic processing, and cognitive effort. Journal ofExperimental Psychology: Learning, Memory, & Cognition, 10,470-482. GRAF, P. (1982). The memorial consequences of generation and transformation. Journal of Verbal Learning & Verbal Behavior, 21, 539-548. HUNT, R. R., & EINSTEIN, G. O. (1981). Relational and item-specific information in memory. Journal of Verbal Learning & Verbal Behavior, 20, 497-514. HUNT, R. R., & MARSCHARK, M. (1987). Yet another picture of imagery: The roles of shared and distinctive information in memory. In M. A. McDaniel & M. Pressley (Eds.), Imagery and related mnemonic processes: Theories, individual differences, and applications (pp. 129-150). New York: Springer-Verlag. HUNT, R. R., & SETA, C. E. (1984). Category size effects in recall: The roles of relational and individual item information. Journal of Experimental Psychology: Learning, Memory, & Cognition, 10, 454-464. JACOBY, L. L. (1978). On interpreting the effects ofrepetition: Solving a problem versus remembering a solution. Journal of VerbalLearning & Verbal Behavior, 17, 649-667.
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NOTES I. In the ANCOVA, 12% of the variance due to treatments could not be uniquely attributed to a specfic treatment effect; consequently, this variance was not included in the main effects tests. If one-third of this variance is assigned to each of the treatments, the main effect of difficulty remains nonsignificant, but if two-thirds of this unincluded variance is embedded into the variance due to difficulty, then the main effect of difficulty becomes significant. Similarly, some of the variance due to the two-way interaction was not included in the two-way interaction tests because it could not be uniquely attributed to a specific two-way interaction. In this case, however, even assigning two-thirds of the nonorthogonal variance to the difficulty x list interaction did not result in a significant difficulty x list interaction effect. 2. In calculating d' scores, when a hit rate of 1.0 or a false alarm rate of 0.0 was encountered, .99 or .01 was used, respectively, to derive the abscissa values of the standardized normal distribution.
(Manuscript received November 21, 1986; revision accepted for publication June 22, 1987.)
