Unconscious Mood-Congruent Memory Bias in Depression

Transcription

1 Journal of Abnormal Psychology Copyright 1996 by the American Psychological Association, Inc. 1996, Vol. 105, No. 1, X/96/$3.00 Unconscious Mood-Congruent Memory Bias in Depression Philip C. Watkins, Karen Vache, Steven P. Verney, and Stephanie Muller Eastern Washington University Andrew Mathews Medical Research Council Applied Psychology Unit The purpose of this study was to investigate an unconscious or implicit mood-congruent memory ( MCM ) bias in clinical depression. Many studies have shown an explicit memory bias, but no study has yet found an implicit MCM bias in clinical depression. The authors compared depressed and control group participants on a conceptually driven implicit memory test. After studying words of positive, neutral, and negative affective valences, participants produced free associations to various cues. Implicit memory or priming was demonstrated by the production of more studied than unstudied words to the association cues. Depressed participants showed more priming of negative words, whereas controls showed more priming of positive words, thus supporting the MCM pattern. Also, no implicit memory deficit was found in depressed participants. These findings are discussed in the context of several prominent theories of cognition and depression. Mood-congruent memory (MCM) may be an important cognitive mechanism in the maintenance of depression. MCM refers to the tendency for depressed or sad individuals to remember information consistent with their mood (i.e., negative or unpleasant memories). Research indicates that MCM is a robust phenomenon in depression (for a review, see Blaney, 1986), and Teasdale (1983) has suggested that MCM might act to maintain depression. If an individual is sad or depressed, MCM indicates that more negative memories are accessible. Recalling these memories tends to maintain or exacerbate the depressed condition, which then leads to the recollection of more negative memories, resulting in a vicious cycle. Teasdale (1983) also suggested that MCM might help explain why depressed individuals tend to avoid effective coping activities. Depression leads to increased recall of negative events. If memory is biased in this fashion, the individual may have lowered expectations regarding the outcome of coping activities, resulting in the avoidance of these coping behaviors. The depressed state is then maintained as the result of the avoidance of effective coping behaviors. For example, ifa depressed person is invited to a party, the tendency to remember negative experiences with parties in the past leads to lowered expectations for enjoyment. These lowered expectations probably lead to the Philip C. Watkins, Karen Vache, Steven P. Verney, and Stephanie Muller, Department of Psychology, Eastern Washington University: A n- drew Mathews, Medical Research Council Applied Psychology Unit, Cambridge, England. Preparation of this article was supported in part by a grant from the Northwest Institute of Advanced Studies. We thank Corby Martin and Robert Carpenter for their assistance in data collection, and Tom Pyle for his advice regarding data analysis. We also wish to express our gratitude to Henry Roediger and Paula Hertel for their comments on drafts of this article. Correspondence concerning this article should be addressed to Philip C. Watkins, Department of Psychology, MS-94, Eastern Washington University, 526 5th Street, Cheney, Washington Electronic mail may be sent via Internet to pwatkins@ewu.edu. avoidance of that party and consequently the avoidance of what might be a mood repair behavior. Thus, investigations of MCM in depression may be important for determining specific cognitive mechanisms that are active in the maintenance of depression. Although MCM has been repeatedly demonstrated (for a review, see Blaney, 1986), almost all of these studies have used explicit or conscious memory measures. In explicit memory tests the individual consciously uses memory, and recall is directed toward a specific learning experience. Most memory research has used explicit memory tests. However, as Mason and Graf have stated (1993), "'we now know, explicit memory is only a small part--the conscious tip of the iceberg--of how memory for recent events influences us in our daily activities" (p. 8). Cognitive psychologists have been investigating unconscious or implicit memory (Roediger, 1990; Schacter, 1987). Implicit memory has been defined as "memory for information that was acquired during a specific episode and that is expressed on tests in which subjects are not required, and are frequently unable, to deliberately or consciously recollect the previously studied information" (Schacter, 1990, p. 338). If MCM is an important maintenance mechanism in depression, it could be argued that this negative bias actually affects adaptive behavior in an unconscious fashion rather than in the conscious way that is usually tapped by explicit memory tests. To return to the earlier example, it seems unlikely that a depressed individual who is considering a party invitation would consciously attempt to remember other party experiences (explicit memory). More likely, memory of past negative experiences unconsciously influences expectations regarding this event. It is possible that an unconscious memory bias in depressed individuals is an important factor influencing their negative view of reality. Thus, an implicit MCM bias may be an important cognitive maintenance mechanism in depression. To our knowledge, only two published studies have investigated MCM in clinical depression with implicit memory tests. Recently, Watkins, Mathews, Williamson, and Fuller (1992) published a study that did not find a MCM bias in implicit 34

2 UNCONSCIOUS MEMORY BIAS 35 memory. In this study they compared depressed and control group participants on an implicit memory test and an explicit memory test. The implicit test used word stem completion (e.g., complete this stem with the first word that comes to mind." los ). The explicit memory test used cued recall and had identical memory cues as the implicit test. Thus, these two measures differed only in whether the participants were consciously using memory. Watkins et al. found the well-demonstrated MCM bias in the explicit memory measure but found no MCM bias in the implicit memory test. Denny and Hunt (1992) conducted a similar study with depressed participants but used word fragment completion as their implicit memory test and free recall as their explicit test. Their results were consistent with Watkins et al.; they demonstrated MCM in the explicit test but did not find this negative bias in the implicit test. In a commentary on these two studies, Roediger and McDermott (1992) made some interesting predictions. They observed that both studies used perceptually driven implicit memory tests, meaning that in these tasks cognitive activities are guided by the perceptual features of the stimuli rather than by the meaning of the stimuli. For example, the meaning of los is not important to completing this word stem with the first word that comes to mind. However, many memory tests do rely on meaningful processing of the stimuli and so are called conceptually driven. Roediger (1990) has pointed out that virtually all explicit memory tests are conceptually driven because the individual must meaningfully relate memory cues to an earlier learning experience. Thus, Roediger and McDermott (1992) argued that the inability to find MCM with perceptually driven implicit tests was not surprising, because word meaning should not be expected to affect tests that do not require conceptual processing. However, they predicted that MCM should be found in implicit memory if conceptually driven tests are used. This prediction follows the transfer-appropriate processing approach, which states that if cognitive processing at study and test are matched, individuals are more likely to recall the information than if processing at study and test are mismatched ( Morris, Bransford, & Franks, 1977). For example, if words are studied in a perceptual fashion but the memory test requires meaningful processing, the transfer-appropriate processing approach would predict that individuals will recall less information than if both the study task and the memory test are meaningfully driven. The purpose of this study was to investigate implicit MCM using a conceptually driven test. We exposed depressed and control group participants to positive, neutral, and negative words in the study phase, then administered a conceptually driven implicit memory test. In this test we presented participants with a series of association cues and asked them to produce as many associates as they could to each cue for 30 s. Using this methodology, studies have found that participants reliably produce more target words that they had seen before than targets they had not studied (Graf, Shimamura, & Squire, 1985; Kihlstrom, Schacter, Cork, Hurt, & Behr, 1990; Srinivas & Roediger, 1990), thus demonstrating implicit memory. Following Roediger and McDermott (1992), we predicted that an MCM bias would be demonstrated with this memory measure. The use of neutral words allowed us to investigate the possibility of a general deficit in implicit memory. To date. one study found an implicit memory deficit associated with depression (Elliot & Greene, 1992), whereas several studies have not found any overall priming difference with neutral materials (Denny & Hunt, 1992; Hertel & Hardin, 1990; Watkins et al., 1992). There is some evidence that although conceptual variables at encoding affect conceptually driven implicit tests, individual differences variables such as amnesia do not result in priming deficits on conceptual tests (Shimamura, 1986). Thus, following Roediger and McDermott ( 1992 ), we predicted that no implicit memory deficit would be associated with depression. A third purpose of this study was to test the elaboration hypothesis of depression proposed by Williams, Watts, MacLeod, and Mathews (1988). They argued that the negative cognitive biases in depression are best explained by the tendency for depressed individuals to elaborate negative information. Elaboration is a more strategic cognitive process, and it is defined as "the activation of a representation in relation to other associated representations to form new relations between them and to activate old relationships" (p. 170). In the test phase of this experiment, participants produced free associations to positive, neutral, and negative cues. If Williams et al. are correct, then depressed individuals should produce relatively more associations to negative cues and fewer associations to positive cues than nondepressed controls. Design and Overview Method This study used a 2 (Group: depressed individuals and controls) x 3 (Word Valence: positive, neutral, and negative) x 2 (Priming: studied vs. unstudied words) mixed factorial design. Repeated measures were Word Valence and Priming. The between-subjects variable was Group. At study, participants were randomly assigned to study one of two word sets. Each word set contained positive, neutral, and negative words. Participants then completed a brief interference task. A free association task followed, which included association cues that were related to words from their studied word set and their unstudied word set. Participants We used two groups of participants in this study: clinically depressed individuals and nondepressed controls. We defined the depressed group as participants with Beck Depression Inventory (BDI) scores of greater than 15 who met the diagnostic criteria for either major depression or dysthymia, as defined by the Diagnostic and Statistical Manual of Mental Disorders ( 3rd ed., rev.: DSM-IH-R; American Psychiatric Association, 1987). Individuals with a reported history of mania were excluded. Diagnosis was determined through a structured interview, the Schedule for Affective Disorders and Schizophrenia, Form C ( SADS-C; Endicott & Spitzer, 1978; see the description below). All interviews of depressed participants were conducted by clinical graduate students. Interviewers made independent diagnoses and then presented interview data to the principal investigator, who made the final determination of the diagnosis. Diagnostic agreement was reached in 94% of the cases. Depressed individuals were recruited from undergraduate psychology classes. A screening study was conducted where students were administered the BDI along with a number of instruments relating to various psychological issues. Individuals with a BDI score of at least 16 were scheduled for the experiment. Depressed participants had to have a BDI score of at least 16 at both screening and the experimental session. We tested 33 individuals through the experimental protocol as potential

3 36 WATKINS, VACHE, VERNEY, MULLER, AND MATHEWS depressed group participants; 13 actually met the criteria described above and were included in the depressed group. No participants were taking psychotropic medications. Control group participants were defined as those individuals who bad BDI scores of 5 or less and who did not meet the DSM-III-R (American Psychiatric Association, 1987) diagnostic criteria for any mood disorder. They also did not report a significant history of depression as measured by the Past Accounts of Sadness Test (PAST; Watkins & Curtis, 1995). Confirmation of diagnosis was conducted through interview with the SADS-C. Controls included in the analysis were matched to depressed participants with regard to gender, and we also attempted to match for age as closely as possible. Each group contained 10 women and 3 men) Mean ages of the depressed and control groups were and 19.15, respectively. Both control and depressed participants who were recruited from psychology classes received partial course credit for their participation. Materials Clinicalmeasures. The BDI (Beck, 1978; Beck & Steer, 1987) was the primary self-report measure that was used for assessing depression level. This is perhaps the most frequently used test in depression research and has good psychometric data supporting its use. To confirm depression diagnosis we used the SADS-C. This interview scale is based on the Research Diagnostic Criteria ( RDC; Spitzer, Endicott, & Robbins, 1975, 1978). Because of the similarity of the RDC and DSM-II1-R (American Psychiatric Association, 1987 ) criteria for depression, this interview is commonly used for confirming depression diagnosis. Form C is a shorter interview but still covers depressive symptoms comprehensively. This form also provides a derived Hamilton Rating Scale for Depression (HRSD; Hamilton, 1960, 1967) score (Endicott, Nee, Cohen, Fleiss, & Sarantakos, 1981). Thus, this interview not only covers the DSM-III-R depression diagnostic criteria, but it also provides a measure of the severity of depression. The PAST is a self-report questionnaire designed to assess an individual's history of depression. It contains a simplified description of the DSM-III-R (American Psychiatric Association, 1987 ) criteria for major depression and for dysthymia. Following each description the participant is asked whether he or she experienced an episode of depression as described. For major depression, participants are also asked to estimate how many episodes of depression they have undergone. At the conclusion of the questionnaire, they are asked several questions relating to their history of depression (e.g. "Have you ever thought about suicide?", "Have you ever felt so depressed you sought help from friends?"). Psychometric data on this instrument appear good. Data were collected on the PAST over several studies with undergraduates from psychology courses. Reliability and validity data were collected from 142 participants. Item to total correlations range from.28 to.61 (mean r =.46), and reliability is adequate (coefficient c~ =.81, 12 items). Validity data also appear good. The total score of the PAST is moderately correlated with the BDI (r =.43). Thus, although it is related to report of current depression, the PAST measures another distinct variable. Similarly, the number of depressive episodes participants report is moderately related to the BD! ( r =.26, p <.01 ). As predicted, women had reliably higher PAST scores than men (t = 2.04, p <.02) and were more likely to report a past episode of major depression (t = 1.63, p <.05 ). There was no difference between the genders in report of past episodes of dysthymia. Thus, data from the PAST roughly correspond to known prevalence patterns. Using this measure, we defined a significant history of depression as two or more episodes of depression. Wordstimuli. The words used in this study were chosen to represent positive (pleasant), neutral, and negative (unpleasant) affective valence. These positive and negative words were derived from past moodcongruent research (e.g., Gotlib, McLachlan, & Katz, 1988; Kuiper & Derry, 1982; see also Watkins et al., 1992, for a description ofa norming study). The positive and negative word groups were roughly equivalent in length and frequency. These words were divided into two equivalent sets consisting of positive, neutral, and negative words (see Table 1 ). One set served as the studied or primed set and the other as the unstudied set for each participant. Each word set consisted of 8 positive, 8 neutral, and 8 negative words. Mean word frequency (using Thorndike & Lorge, 1944) for Word Set A was words per million (SD = ), and word frequency for Set B was words per million (SD = 27.67). Mean length of words was 8.04 letters (SD = 1.65) for Set A and 7.25 letters (SD = 0.99) for Set B. In each group, Set A served as the primed set for 7 participants, and Set B was the primed word set for 6 participants. We conducted an analysis to determine whether word set had any effect on priming. Word set did not interact with priming, F( 1, 24) = 0.50, ns, and no interactions with word set involving Group, Valence, and Priming reached significance. All words chosen for the study task were moderately related to certain cue words. In a pilot study, we asked participants to produce associations to a number of positive and negative cues. We then chose targets from the words that several, but not most, participants produced to the cues. This selection criteria was used so that most participants would not produce the unstudied target words in the association task. If participants produced a high number of unstudied targets, then a differential priming effect would be ditficult to demonstrate. Neutral words and cues were chosen from those used by Srinivas and Roediger (1990). Some lack of equivalence existed between the emotional and neutral words in that the positive and negative words were adjectives and the neutral words were not. Apparatus The word stimuli were presented in the study phase on an IBM-compatible computer. Likewise, the distractor task and the association cues in the test phase were also presented by computer. The presentation of the stimuli was programmed through the Micro Experimental Laboratory software package Schneider, 1988). Procedure Following the screening study, appropriate participants were called and scheduled for experimental sessions. After reading and signing the consent form, they were introduced to the study phase of the experiment. They were first randomly assigned to be exposed to one of the two word sets as described above. The set they were assigned to would serve as their studied (primed) word set, and the set they were not assigned to served as their unstudied word set (unprimed). Participants were told that a number of words would appear on the screen, one at a time, and that their task was to attempt to imagine themselves in a scene that involved themselves and the word presented. They were instructed to press a button on the computer keyboard "as soon as you have a clear image of the scene." Following a 1 s "get ready" prompt, each stimulus word appeared on the screen for 15 s. After imagining each scene, participants were asked several questions about the scene: (a) they were asked whether the scene was an actual scene from their past or an imaginary one, (b) they were asked whether they were the principal character of the scene, (c) they were asked to rate the vividness of the scene on a 9-point Likert-type scale, and (d) they were asked to rate the pleasantness-unpleasantness of the scene on a 9-point Likert-type scale. Following this sequence, the next stimulus word was presented. Five A total of 22 participants who met the criteria for the control group completed the experimental protocol. Statistical analyses comparing the entire group of controls to the depressed group yielded essentially identical results as that reported here.

4 UNCONSCIOUS MEMORY BIAS 37 Table l Association Cues and Targets by Valence and Word Set Valence Word set Positive Neutral Negative Adored-Admired Attractive-Desirable Approval-Supported Hopeful-Optimistic Loved-Appreciated Respected-Liked Successful-Accomplished Creative-Talented Awarded-Praised Capable-Competent Fulfilled--Gratified Outstanding-Superior Smart-Witty Triumph-Overcome Valuable-Needed Worthy-Accepted Clothing-Sweater Furniture-Dresser Kitchen utensils-spatula Musical instrument-piccolo Sports-Bowling Senses-Hearing Types of cloth-flannel Vegetables-Cabbage Animals-Giraffe Colors-Magenta Fruits-Peaches Fuels-Propane Parts of a car-muffler Reptiles-Turtles Sciences-Geology Trees-Willows Blamed-Punished Bleak-Hopeless Criticized-Judged Discontent-Unsatisfied Hated-Detested Isolated-Abandoned Mistake-Failure Ugly-Unwanted Downcast-Gloomy Empty-Lonely Guilty-Accused Humiliated-Ashamed Ignored-Neglected Inadequate-Unworthy Unlovable-Rejected Worthless-Useless Note. In each pair, the first word or phrase is the cue, and the word following the dash is the target. practice trials were presented, followed by the experimental trials. Stimulus words were presented in random order. After the presentation of the 24 words in the study phase, all participants were exposed to a brief distractor task. They were shown an array of numbers or letters (or both) on the screen, and their task was to determine as quickly as possible whether there was a letter m located in the array. None of the letter arrays formed a legitimate English word. This task took approximately 30 s to complete. Participants were then introduced to the test phase. In the introduction of this phase an attempt was made to dissociate study and test. They were asked to participate in a "developmental experiment" and were told that we needed to "develop some materials for a future experiment." They were told that their task was to produce as many oneword associations to the cue words as possible and that for some words (categories) the best way to produce associations was to list as many instances of the category as possible. However, other cues were not clearly categories, and with these words "you will probably produce more associations if you think of words that are closely related to the word (like synonyms)." In each trial, a "get ready" prompt appeared on the screen along with a tone (to reorient the participants ). Following the prompt, a cue word appeared and the participant was instructed to produce as many associations to the word as possible. Each association cue remained on the computer screen for 30 s. Participants were given one practice trial, which was then followed by 48 experimental trials. Each of the 48 cue words was related to one of the words from either the studied or unstudied word lists. Responses were recorded through audio tape, and the experimenters also made a written record of the critical responses. Immediately following the free association task, participants were administered the BDI, PAST, and other measures. Then the experimenter administered the SADS-C interview. Finally they were debriefed. The debriefing interview included open-ended questions regarding the participants' perceptions of the purpose ofthe study. Second, we asked participants how they came up with the associations in the free association task. We also asked more direct questions regarding the participants' awareness of the memory components of the implicit test. For example, we asked them whether they were "consciously trying to come up with word associations that were from the imagination task." (All participants responded "'no.") We also asked whether they thought "that the free association task was a memory test" while they were performing the association task. Then we asked them whether they noticed that some of the associations they produced were from the words in the encoding task. Finally, we included a question regarding their estimation of the percentage of positive and negative words in the encoding task. Participant Characteristics Results Mean BDI scores were (SD = 9.27) for the depressed group and 2.69 (SD = 1.70) for the controls. Mean derived HRSD scores were (SD = 7.71 ) and 4.58 (SD = 2.23 ) for the depressed and control groups, respectively. Analysis of Associations To test the hypothesis that depressed participants elaborate negative information more than controls, we conducted a 2 (Group) X 3 (Cue Valence) repeated measures analysis of variance (ANOVA) for number of unstudied associations produced. Any association that a participant produced that was not a studied target was included in this analysis. Group was a betweensubjects factor and Cue Valence was a within-subjects factor. We present this analysis prior to the priming analysis because the results bear on how we conducted the priming analysis. Means for number of associations produced are shown in Table 2. A large main effect for Cue Valence was found, F( 2, 48 ) = l, MSE = , p <.000 I. This was due to all participants producing a much larger number of associations to neutral cues (see Table 2). As predicted, the Valence X Group interaction was also significant, F(2, 48 ) = 3.26, MSE = , p <.05. We investigated this interaction by forming an association bias score by subtracting the number of associations produced to negative cues from the number of associations produced to positive cues. We then compared the groups with a t test, and the

5 38 WATKINS, VACHE, VERNEY, MULLER, AND MATHEWS Table 2 Number of Unstudied Associations Produced as a Function of Group and Valence Control Group Depressed Valence M SD M SD Positive Neutral Negative group differences were found to be reliable, t = 2.53, p <. 05. The mean positive association bias score for controls was 11.62, and the mean for depressed participants was Priming Analysis An association was coded as a target if the participant produced one of the targets from either the studied or unstudied target list. Different forms of the words (e.g., failed instead of f~ilure) were coded as targets produced. Acceptable responses were defined prior to data collection. Synonyms and words related to targets were not coded as targets. For example, unsuccessful or loser were not coded as targets for the word failure. If a participant produced a target more than once, this was counted as only one target produced. Prior to conducting our primary analysis,we first analyzed number of unstudied targets produced by Group and Valence. No main effect for Group was found, F( 1, 24) = 0.38, MSE = 1.21, n s; the interaction between Group and Valence was not significant, F(2, 48) =.72, MSE = 1.02, ns. Thus, the groups did not differentially respond on our baseline measure. However, a main effect of Valence was found, F(2, 48 ) = 8.31, MSE = 1.02, p <.05. This effect paralleled our finding with the association analyses described earlier, in that participants produced more neutral unstudied targets than positive or negative. In our primary analysis we conducted a 2 (Group) X 2 (Priming) x 3 (Valence) repeated measures ANOVA for number of targets produced. Number of targets produced included words produced that were from either the studied or the unstudied word lists. Means for number of targets produced are shown in Table 3. No main effect was found for Group, F( 1, 24) = 0.58, MSE = 2,84, ns, indicating that the two groups did not differ in overall number of targets produced. A strong effect for Priming was found, F(1,24) = 63.50, MSE = 1.60, p <.0001, indicating the existence of an implicit memory effect. A main effect was found for Valence, F( 2, 48 ) = 13.44, MSE = 1.1 O, p < This was due to all participants producing more studied and unstudied neutral word targets. Neutral words were not primed easier than positive or negative words, however. This was demonstrated by the absence of a Priming X Valence interaction, F(2, 48) = 0.45, MSE =.89, ns. Most importantly (and as predicted), the three-way interaction between Group, Priming, and Valence was significant, F(2, 48) = 5.21, MSE = 0.89, p <.05. The nature of our finding is depicted in Figure 1. This figure was formed by creating prim- ing scores for each valence by subtracting the number of unstudied targets produced from the number of studied targets, thus incorporating the priming factor into the figure. This number was then turned into a proportion by dividing it by 8 (the maximum priming score a participant could receive in a valence category). As is evident from this figure, the pattern of means for the two groups conforms to a mood-congruent pattern. To explore this interaction further, we compared the groups with planned orthogonal contrasts of priming scores by Valence. We found that the control group had significantly higher priming scores for positive targets than did depressed participants (p <.05), and conversely depressed participants had significantly higher priming scores for negative targets (p <.05). The groups did not differ with regard to priming of neutral targets (p =.90), thus showing no implicit memory deficit for depressed participants. Because of the group and valence differences in number of associations produced, it could be argued that the number of opportunities that existed for producing a target was not equivalent across valences. Thus, we formed a dependent variable that accounted for the number of associations produced. We formed scores for each participant that represented the percentage of targets produced of the total number of associations produced for each valence condition. We then conducted a 2 (Group) 3 (Valence) 2 (Priming) repeated measures ANOVA. Confirming our primary analysis, the interaction between Group, Valence, and Priming was significant, F(2, 48 ) = 3.46, MSE = 2.27, p <.05. Discussion This study represents the first demonstration of an MCM bias on a conceptually driven implicit memory test. Depressed participants were found to have greater priming of negative words Table 3 Mean Number ql'target Words Produced as a Function of Group, Valence, and Priming Control Group Depressed Valence M SD M SD Positive Studied targets , Unstudied targets Difference (priming) Neutral Studied targets Unstudied targets Difference (priming) Negative Studied targets Unstudied targets Difference (priming) Total Studied targets Unstudied targets Difference (priming)

6 UNCONSCIOUS MEMORY BIAS 39 Figure 1. Mean priming proportion by group and word valence. Priming proportion is number of studied minus unstudied targets produced, divided by the maximum priming score ( 8 ). and less priming of positive words than controls. We believe this finding may have important implications for understanding depression. It may be that the negatively colored view of the world exhibited by depressed individuals and their avoidance of activities that may help repair their mood are influenced by this unconscious negative memory bias. Although this study may lack some generalizability in that the depressed participants were college students, a recent review has shown that there is little reason to believe that findings from depressed college students are different from depressed individuals at large (Vredenburg, Flett, & Krames, 1993). We agree with Coyne (1994) that Vredenburg et al. confused the question "Are depressed college students different from depressed subjects at large?" with "Are college students with elevated BDI scores different from depressed subjects at large?" However, Coyne's critique does not appear to preclude generalizing from a properly diagnosed depressed college population. The finding of the current study contrasts with two other studies that did not find an implicit MCM bias (Denny & Hunt, 1992; Watkins et al., 1992 ). As pointed out earlier, both of these studies used perceptually driven implicit memory tests, whereas we used a conceptually driven test. It seems that the most straightforward way to interpret this pattern of results is to assert that conceptually driven processes at test reveal MCM in depression, whereas perceptually driven processes do not. Although we believe this to be the case, other explanations, such as increased sensitivity of the test and use of different word sets, are also possible. Often, mood state-dependent recall and MCM are conceptually linked in theories of emotion and cognition (e.g., Bower, 1981). It is of interest to note that the pattern of findings in implicit MCM appears to be consistent with that found in mood state-dependent recall research. Using a musical mood induction methodology, Eich and associates have found evidence of mood state-dependent recall in conceptually driven implicit memory measures, but not in perceptually driven implicit tests (for a review of these studies, see MacAulay, Ryan, & Eich, 1993). One difference in the pattern of findings between implicit tests could be due to participants being more aware that conceptually driven tests involve memory than the perceptually driven tests (see Bowers & Schacter, 1990). Data from the debriefing interviews in this study seem to contradict this hypothesis, however. In the current study, 42% of the participants claimed they did not recognize that they had produced any associations from the study phase. In the Watkins et al. (1992) study, 96% of the participants recognized that they used studied words to complete the word stems. Because almost half of the participants in the current study were unaware that they had produced any studied targets, we defined these participants as memory unaware and re-analyzed our data with this memory awareness factor. This analysis showed no significant interactions with the other factors (i.e., Group, Priming, Valence). Thus, awareness of the memory-based aspects of the implicit test appeared to have no impact on the implicit MCM effect found here. It could be argued that referring to our finding as an unconscious memory bias is problematic (see Schacter, Bowers, & Booker, 1989). After all, 58% of our participants had at least some awareness of the memory aspects of the experiment. We hold that the conscious aspects of this study are largely epiphenomena, that is, participants unconsciously (unintentionally) produced a studied target and then recognized that the association was from the study task. In a series of studies using perceptual identification as their implicit test, Richardson-Klavehn, Lee, Joubran, and Bjork (1994) showed that the principle difference between implicit and explicit tests was in whether the individuals used intentional recollection. Thus, implicit memory tests appear to be tapping incidental retrieval. In fact, all of our participants stated that they were not "consciously trying" to recall items from the study task. However, most were aware that some of their associations were studied targets. Thus, it is possible that they can unconsciously retrieve an item and then become consciously aware that the item was previously studied. Future research may determine whether a participant's awareness that an item was previously studied affects subsequent retrieval. In this study, however, test awareness had no impact on the variables of interest. How does our primary finding here fit with prominent theories of cognition and sadness-depression? It seems that a conceptually driven MCM bias would be consistent with the spreading activation approach of Bower ( 1981 ) and the schema theory of Beck (Kovacs & Beck, 1978). However, neither of these theories make specific predictions about cognitive biases in implicit memory. Even if we deduce from these theories the prediction of a conceptually driven MCM bias, it would be difficult for these theories to explain the absence of MCM with perceptually driven tests. The lack of a mood-congruent bias in perceptually driven tests and our finding of MCM in a conceptually driven test appear to be handled by the approach of Wil-

7 40 WATKINS, VACHE, VERNEY, MULLER, AND MATHEWS liams et al. (1988). They argue that the cognitive bias in depression is limited more to elaborative processes rather than the initial "pick up" or activation of the information in memory. If we concede that elaboration is a conceptually driven process, then the Williams et al. approach seems to account for the pattern of findings. In fact, several studies have shown that the manipulation of conceptual variables at encoding affect conceptually driven tests much like they influence explicit memory tests (Blaxton, 1989; Hamann, 1990; Smith & Branscombe, 1987, 1988; Srinivas & Roediger, 1990). These conceptual manipulations have little or no effect on perceptually driven implicit memory tests (for a review, see Roediger, 1990). We also tested the elaboration hypothesis of Williams et al. (1988) by comparing the number of associations produced to the valenced cues between the two groups. As predicted, a mood-congruent pattern was found. This finding clearly seems to support the elaboration hypothesis. This study also speaks to the issue of whether an implicit memory deficit exists in depression. Although several studies did not find an implicit deficit in depression and sadness (Denny & Hunt, 1992; Hertel & Hardin, 1990; Watkins et al., 1992), one study found that depressed individuals did show an implicit memory deficit with word stem completion and homophone spelling (Elliot & Greene, 1992). Although Roediger and McDermott (1992) pointed out some methodological difficulties with this study, they concluded that these problems could not account for the priming deficit demonstrated by Elliot and Greene (1992). Our result here agrees with the findings of the other studies that used perceptually driven tests. Thus, as predicted by Roediger and McDermott (1992), the bulk of the data suggests that implicit memory is intact in depression. Depression, like amnesia and age, is related to a deficit in explicit memory, but does not appear to impair implicit memory (e.g., Graf, 1990; Schacter, 1985 ). To summarize, this study represents the first demonstration of an implicit MCM bias in clinical depression. This was demonstrated with a conceptually driven implicit test. By eontrast, perceptually driven tests have not revealed MCM in clinical depression (Denny & Hunt, 1992; Watkins et al., 1992). Thus, as predicted by Roediger and McDermott (1992), conceptually driven implicit memory appears to conform to the same pattern as that of explicit memory, in which MCM has frequently been demonstrated in depression (Blaney, 1986). Second, no implicit memory deficit was found with depressed individuals. 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