depression and implicit memory: understanding mood congruent memory bias

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Cognitive Therapy and Research [cotr] PP1233-cotr-488231 May 13, 2004 19:48 Style file version Jun 14th, 2002

Cognitive Therapy and Research, Vol. 28, No. 3, June 2004 ( C© 2004), pp. 387–414

Depression and Implicit Memory: Understanding MoodCongruent Memory Bias

Elaine S. Barry,1,2,3 Mary J. Naus,1 and Lynn P. Rehm1

The present paper reviews the depression and implicit memory literature, emphasizingstudies addressing possible mood congruent implicit memory biases in depression.Although some of these studies seem to indicate the presence of mood congruent bi-ases in implicit memory, others fail to show this effect. Although the studies differ ona variety of dimensions (participant population, sample size, implicit memory task,depressive status, etc.), a thorough review of the literature suggests that these are notthe most important considerations in understanding the presence or absence of moodcongruent memory biases in depression. Rather, the cognitive framework of TransferAppropriate Processing is used as a tool to organize and explain these findings. Inparticular, the role of perceptual and conceptual cognitive processes by depressed par-ticipants performing implicit memory tasks are examined in the context of perceptualand conceptual task demands. Examining unconscious influences on emotion couldhave important implications for understanding and treating depression.

KEY WORDS: depression; implicit memory; mood congruent bias.

In the past two decades, clinicians attempting to understand and treat depressionhave increasingly turned to research and theories from cognitive psychology, andespecially memory, to advance their efforts (e.g., Eysenck, 1991; Ingram, Miranda, &Segal, 1998; Rehm & Naus, 1990; Teasdale, Lloyd, & Hutton, 1998; Williams, Watts,MacLeod, & Mathews, 1997). Similarly, cognitive psychologists are increasingly usingdepressed individuals in research studies as an empirically based method to betterunderstand the workings of a normative cognitive system (e.g., Bradley, Mogg, &Millar, 1996; Bradley, Mogg, & Williams, 1994; Rathus, Reber, Manza, & Kushner,1994). Indeed, cognitive researchers such as Colin MacLeod and Andrew Mathews

1Department of Psychology, University of Houston, Texas.2Present address: The Commonwealth College of The Pennsylvania State University, Division of Healthand Human Development, Uniontown, Pennsylvania.

3Correspondence should be directed to Elaine S. Barry, Human Development and Family Studies, PennState Fayette, One University Drive, Rt. 119 N., P. O. Box 519, Uniontown, Pennsylvania 15401; e-mail:[email protected].

387

0147-5916/04/0600-0387/0 C© 2004 Plenum Publishing Corporation

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388 Barry, Naus, and Rehm

have strongly encouraged the union of laboratory work on cognition with clinicalresearch on psychopathology (e.g., MacLeod & Mathews, 1991).

Within traditional laboratory work on cognition, some cognitive psychologistschose to focus on the distinction between implicit memory and explicit memory(e.g., Bowers & Schacter, 1990; Graf & Schacter, 1985; MacLeod, 1989; Richardson-Klavehn & Bjork, 1988; Roediger, 1990; Schacter, 1987), even though historically,most cognitive memory research concentrated on explicit, declarative memory. Itwas in the context of explicit memory research that several cognitive models ofemotion were developed during the 1990s. Although a comprehensive review of allof these models is beyond the scope of this paper, excellent reviews can be foundin Eysenck (1991) and Ingram et al. (1998). However, for illustrative purposes, wewill briefly describe several different cognitive models of emotion based on memory(e.g., Beck, 1987; Rehm & Naus, 1990; Riskind, 1989; Williams et al., 1997; Williams,Watts, MacLeod & Mathews, 1988). The Bower (1981, 1987) model would also beincluded in this category, and it is reviewed in the section below called Priming.

Beck’s cognitive model of depression (Beck, 1987) proposed that depression isbased in depressive schemas that result in distorted cognitions that result in automatic(negative) thoughts. According to his model, individuals prone to developing depres-sion have “depressogenic schemas” that remain latent until activated by stressful lifeevents. After activation, these negative schemas provide the individual with access tonegative cognitive processing that results in depression. The Rehm and Naus (1990)memory model of emotion attempted to incorporate then current models of mem-ory into a comprehensive theory of depression. Central to this model is the ideathat the information processing of the depressed individual is emotionally biased. Inaddition, the emotional quality of experience is an important feature that is storedin semantic memory schemas and also influences how new and old information isinterpreted. Riskind’s model (Riskind, 1989) was based on the centrality of cogni-tive priming (discussed in the next section of this paper) and redefining mood as acognitive state rather than a subjective feeling. Thus, “cognitive phenomena are thenucleus of the depressed mood” (Riskind, 1989, p. 182). In this model, self-referenteffects (“interactive encoding”) take a special place, as negative schemas are primedby negative views of the self and the environment. In the literature review providedin the current paper, self-referent effects are noted when they appear in the research.Finally, Williams et al. (1988, 1997) present a model of depression and anxiety whichtakes a processing approach. In their model, initial priming and subsequent elabora-tion are central considerations. Additionally, Williams et al. attempted to specify whyprocessing biases may differ for different emotional disorders. Further, their modelassumes that emotions arise to serve biological and social functions that need to beaddressed in treating emotional disorders.

At the time these models were proposed, studies of the relationship betweendepressed emotion and implicit memory were not available for consideration. In theintervening decade, however, research concerning depression and implicit memoryhas proliferated, and the growing numbers of studies with empirical data now demandthat a comprehensive model of memory and depression incorporate implicit memoryfindings. The purpose of this paper is to review the literature on depression andimplicit memory to lead to a better understanding of mood congruent memory bias.

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Depression, Implicit Memory, and Mood Congruency 389

IMPLICIT MEMORY

In their landmark paper, Graf and Schacter (1985) defined the terms implicitand explicit memory in the following way: “Implicit memory is revealed when per-formance on a task is facilitated in the absence of conscious recollection; explicitmemory is revealed when performance on a task requires conscious recollection ofprevious experiences” (p. 501). For example, say you see a squirrel run across theroad on your drive into work. Later, someone asks you to name the first animal youcan think of. Without consciously recalling the squirrel from earlier in the day, youquickly answer “squirrel.” In this case, your memory of the squirrel would appear tohave been produced without your awareness. This is implicit memory at work. In fact,you may not even recall the squirrel that ran across the road if someone asked whatanimals you had seen during the day. That type of direct question, with its subsequentconscious search of memory, is an example of explicit memory. Thus, explicit mem-ory refers to conscious memory, whereas implicit memory usually refers to memorywithout awareness. What is unclear, however, is whether explicit and implicit mem-ory refer to the memory task (a specific methodology) or to the memory process (amental event). Dunn and Kirsner (1989) and Richardson-Klavehn and Bjork (1988)have noted that these terms unfortunately have been used in the cognitive literatureto refer both memory tasks and memory processes.

Transparency Assumption

Traditionally, the task used to measure memory defines the type of memory thatis studied. Since Graf and Schacter’s classic (1985) paper, tasks that can be performedwithout conscious awareness of the study episode (such as word stem completionor word fragment completion, described in more detail below) have been used toexamine implicit memory. Similarly, traditional episodic tasks requiring consciousreference to the study episode (such as free recall or recognition) have been usedto examine explicit memory. Thus, the term “Transparency Assumption” (TA) wascoined by Dunn and Kirsner (1989) to describe the notion that a given memory task(i.e., an “implicit” task like word stem completion) reflects an identical underlyingprocess (i.e., implicit memory). In their words, the TA holds that “tasks functionas transparent windows to underlying mental processes” (Dunn & Kirsner, 1989,p. 18).

This assumption, however, could logically only be true under certain special cir-cumstances. Unless all of these circumstances are met simultaneously (which is highlyunlikely), there is no reason to assume that the task mirrors the process. For example,a patient with amnesia who has impaired episodic memory may demonstrate implicitmemory when completing a series of word stems (e.g., Graf & Schacter, 1985). Inthis case, the patient has no conscious recollection of the study episode, and the taskis designed in such a way that performance on the task can be enhanced by prior pre-sentation of a list of words. Thus, word stems may be completed with more previouslypresented words by amnesic patients compared to controls (who have had no studyepisode), and this occurs without conscious awareness. This scenario represents asituation in which the task (word stem completion) would appear to represent the

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underlying process (implicit memory). However, the case becomes more complicatedwhen nonimpaired participants are involved instead of neuropsychological patients.In the case of nonimpaired participants, performance on a word fragment comple-tion task might be contaminated by explicit recollection (e.g., Roediger, Srivinas, &Weldon, 1989). That is, a participant completing a list of word fragments may be-come aware that some of the words had been presented in the prior list. Thereafter,he or she could enhance performance on the task by purposely recalling the studyepisode and using explicit strategies to search for previously encountered words thatwould complete the fragments. In fact, Graf, Squire, and Mandler (1984) and Squire,Shimamura, and Graf (1987) have both demonstrated that explicit remembering bycontrols could account for their enhanced performance (compared to amnesic pa-tients) under implicit instructions to remember. Although some empirical studiesof implicit memory have addressed this potential confound, the majority of studiesseem to ignore it at worst, or pay lip service to it at best. Despite this importantand substantive theoretical point regarding task and process, however, in the reviewportion of this paper the terms “implicit memory” and “explicit memory” are usedto reflect the author of the studies’ use of these terms.

Priming

The premiere method for measuring implicit memory is through priming. Tulvingand Schacter (1990) state, “[p]riming is a type of implicit memory” with affiliations to“both procedural and semantic memory” (p. 301). Traditionally, the study of primingemploys the popular cognitive semantic network model of memory, in which memoryis conceptualized to have a structure made up of nodes (e.g., Anderson, 1983; Collins& Loftus, 1975). Nodes may represent concepts, events, ideas, or propositions, andmemory “happens” when spreading activation between nodes in this network causesthe information contained within the nodes to become conscious (Bower, 1987). Inthe case of explicit memory, the memory becomes conscious and the person is usuallyaware of the result. For example, when trying to remember the name of a movie,one might remember that it has a color in the title. One may then begin searchingone’s memory for the names of colors, and the name of the movie then “pops”into consciousness. A successful search of memory, and the person is aware of theresult. For implicit memory, it happens a little differently. The priming phenomenonallows researchers to determine the effect that spreading activation has had on itemswithin the memory network, even those of which the person may not be aware.The basic premise is that once nodes are activated, their activation spread to other,nearby nodes. Once these nodes are activated, the concepts may become conscious,although there is often no overt realization (or awareness) on the part of the personthat the concept was somehow related to the originally activated node.

Consider the squirrel example given earlier. A squirrel is an animal, and sothe “squirrel” node is connected in the memory network with the “animal” node.Later, after the squirrel encounter, when asked to give the name of an animal, the“animal” node is activated, and that activation spreads to the “squirrel” node. Thus,“squirrel” becomes conscious, even though the person is not aware that this responseis due to his or her earlier encounter, which may not even be explicitly remembered.

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Why is “squirrel” activated after hearing “animal,” rather than one of thousands ofother animals that are also connected to the node in the network? According to thenetwork model, it is because the earlier encounter with the squirrel also activated the“squirrel” node, and that recent experience left some residual activation, loweringthe threshold required for activating that concept again. Everything else being equal,then, when the “animal” node is activated, some amount of activation spreads to the“squirrel” node as well as to other, nearby nodes. The activation newly spread to the“squirrel” node combines with the residual activation from the earlier experience.This combined activation surpasses the threshold necessary to activate “squirrel” andbring it to consciousness. Priming is usually measured by decreased reaction timesto respond to stimuli, increased recognition and/or liking of represented stimuli,increased perceptual ability for degraded stimuli, or other responses that indicate aneffect of previous exposure of stimuli on the current task. More specific informationregarding the use of priming to measure implicit memory will be discussed in theliterature review that follows.

Bower and Mood Priming

In addition to the traditional cognitive priming described above, mood primingis of particular importance to understanding depression. Bower (1981) formally in-troduced an associative network theory of memory and emotion, based in part on thenetwork theories of Collins and Loftus (1975) and others, as described above. In ad-dition to concept and proposition nodes, Bower proposed emotion nodes as memoryunits. He later referred to these as “special purpose emotion nodes” (Bower, 1987,p. 443). In Bower’s model, links to emotions and any related concepts, includinginternal physiological arousal, episodic information, linguistic concepts, and othersemantic links, are considered to have bidirectional influence. In other words, emo-tion nodes will be activated by experiencing the emotions again or by activation ofany of their links. Importantly, once these nodes are activated, the categories thatare primed are then used to interpret “the somewhat ambiguous social events thatgo on around us” (Bower, 1987, p. 444). For example, say you are dining at a restau-rant when you receive bad news. The bad news activates negative emotion nodes,which are then linked to the restaurant. The next time you are at the restaurant,these negative emotion nodes may again be activated, even without your awareness(priming). In this way, an ambiguous situation (ex. slow waitstaff, a mistaken drinkorder, etc.) may be interpreted negatively (“it’s because of what I am wearing” or“I always get treated badly”). Thus, Bower’s theory accounts for both cognitive andemotional phenomenon. The research reviewed in this paper is comprised of em-pirical mood priming studies, which Ingram, Miranda, and Segal (1998) point outare derived from, and test, models of mood and memory. The models most of thesestudies are testing were described in the introduction to this paper.

DEPRESSION AND IMPLICIT MEMORY

As mentioned previously, in the past two dozen years there has been enoughresearch interest in the area of depression and implicit memory to warrant a serious

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examination of the literature. Unfortunately, the literature on the effects of depres-sion on implicit memory has not enabled interested researchers to reach a consensusregarding these effects. In the past dozen years there have been at least that manyresearch studies investigating depression and implicit memory, falling into two dia-metrically opposed camps. Seven studies showed no significant differences in implicitmemory tasks by depressive status (Bazin, Perruchet, & Feline, 1996; Bazin, Per-ruchet, DeBonis, & Feline, 1994; Danion, Kauffmann-Muller, Grange, Zimmermann,& Greth, 1995; Denny & Hunt, 1992; Ilsley, Moffoot, & O’Carroll, 1995; Lang &Craske, 1997; Watkins, Mathews, Williamson, & Fuller, 1992), whereas eight otherstudies showed better memory performance in mood-congruent implicit memorytasks by participants classified as depressed (Bradley et al., 1994, 1996, Expts. 1 and2; Bradley, Mogg, & Williams, 1995; Ruiz-Caballero & Gonzalez, 1994, Expts. 1 and2; Ruiz-Caballero & Gonzalez, 1997; Watkins, Vache, Verney, Muller, & Mathews,1996). One study actually found that depressed individuals performed worse thancontrols on a neutral implicit memory task (Elliott & Greene, 1992), three studiesshowed no performance deficits by depressed participants (Danion et al., 1991; Her-tel & Hardin, 1990; Jenkins & McDowall, 2001), and a review of four early studiessuggested that mood-congruent memory (MCM) effects may be found in implicitmemory tasks, despite the nonsignificant nature of the reported results (Roediger& McDermott, 1992). These 19 studies differ along several different dimensions,including depressive status of participants (clinical depression, dysthymia, elevatedBeck Depression Inventory scores, or induced negative mood), hospitalization andmedication status (inpatient/outpatient and medicated/nonmedicated in virtually allpossible combinations), type of materials used (emotionally valenced words or neu-tral words), implicit memory task (word stem completion, word fragment completion,lexical decision, or word associations), levels of processing (primarily perceptual orprimarily conceptual), and instructions to remember (intentional or incidental encod-ing). A critical review of the findings is needed to judge what effect, if any, depressionhas on implicit memory.

Tasks

Each of the studies reviewed used one of four implicit memory tasks to mea-sure priming. A summary of these tasks appears in Table I. The first task listed inTable I is the lexical decision task. In this paradigm, words are presented briefly toparticipants, masked, and then presented again (or a nonword is presented, for “no”trials). The first presentation of the word (the “prime”) is too brief to be reliablydetected by the participant, and awareness checks are usually performed to ensurethat participants perform at chance levels when attempting to determine whetherthe prime is a word or a nonword. After the second presentation of the word (the“target”), the participant is to respond as quickly as possible as to whether or notthe target letter string is a legitimate English word (“yes” or “no”). When the primeword is the same as the target word (or is a related word), and the reaction time torespond “yes” to the target word is reduced, priming is said to have occurred.

Another type of task appearing in Table I is the word fragment completion task.In this task, the participant is presented with a list of words under either intentional or

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Table I. Implicit Memory Tasks and Measures of Priming

Task Example Measure of priming

Lexical decision (priming) Present “banana” very briefly,then present “banana,”participant is to respond asto whether or not the secondpresentation forms a word.

Quicker to respond “yes” towords that were brieflypresented previously.

Word fragment completion Complete the following word,ba a

More likely to complete with“banana” after beingpresented with the word“banana” in an incidentalstudy phase.

Word-stem completion Complete the following word,ban

More likely to complete with“banana” after beingpresented with the word“banana” in an incidentalstudy phase.

Word associations “Name a fruit” and participantresponds, “banana.”

More likely to respond“banana” after beingpresented with the word“banana” in an incidentalstudy phase.

incidental encoding conditions. Some time later (minutes to weeks), participants aregiven a list of fragmented words where certain key letters (usually consonants) aremissing from the word to be completed (ex. a a in, to be completed into assassin).The participant is to complete each fragment with the first word that comes to mind.No mention is made of the earlier study episode, and usually half of the word stemscan be completed with words from the previous list. Priming is measured as the extentto which the number of fragments completed using words from the previously studiedlist exceeds baseline performance (the number of unstudied fragments completed).

The most commonly used task in the depression and implicit memory literaturereviewed herein is word stem completion, which is the third task described in Table I.Like the word fragment completion task, in this task, the participant is presented witha list of words under either intentional or incidental encoding conditions. Some timelater, and again without reference to the study episode, the participant is given alist of three-letter word stems and asked to complete each stem with the first wordthat comes to mind. Priming is measured in the same way as for word fragmentcompletion.

A final implicit memory task listed in Table I and used in this group of experi-ments is a “conceptual” implicit memory task. Like word stem completion and wordfragment completion, this task requires participants to be presented with a list ofwords under either intentional or incidental learning conditions. Then, at some laterpoint, participants are asked to provide word associations to experimenter-providedcues. To the extent that words from the previously presented list appear as prod-ucts of this association, priming has occurred. Compared to the other types of tasks,however, this task seems to require a different kind of processing on the part of theparticipant. A theoretical distinction has been made (Roediger et al., 1989) between“perceptual” implicit memory tasks (like the first three tasks described here), and

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“conceptual” implicit memory tasks (like the last one described here). These termsrefer to the type of cognitive processing required to complete the task. In short,perceptual implicit memory tasks are more “shallow” or data-driven tasks, requiringless cognitive effort. Conceptual implicit memory tasks, on the other hand, are more“deep” or conceptually driven tasks that require at least some cognitive effort. Thisdistinction is further explored in the section entitled “Why the Equivocal Results inthe Literature?,” after the depression and implicit memory research is reviewed.

Mood Congruent Memory

The research to be reviewed herein primarily centers on the concept of mood-congruent memory. Mood-congruent memory (MCM) occurs when “people attendto and learn more about events that match their emotional state” (Bower, 1981,p. 147). That is, when the mood of the events or material during the learning episodeis matched by the current mood, the result is better memory performance duringmemory retrieval. For this reason, mood-congruent memory is often confused withmood-state-dependence, which Bower (1981) described as occurring when “peoplerecall an event better if they somehow reinstate during recall the original emotionthey experienced during learning” (p. 147). The distinction between the two conceptsis rather fine, and this has implications for research regarding both of these moodand memory effects. The mood-state dependent effect has been found to be difficultto replicate and inconsistent in its appearance (Blaney, 1986; Bower, 1987; Bower& Mayer, 1985; Riskind, 1989; Ucros, 1989; Wetzler, 1985). In his analysis of theliterature, Riskind (1989) noted that “[i]n general, mood state-dependent memoryis not a stable laboratory phenomenon; however, significant state-dependent effectsdo occur fairly frequently” (p. 180). Riskind continued, explaining the conditions un-der which mood state-dependent effects and mood-congruency effects occur in hiscognitive model of emotion described earlier. According to his analysis, mood state-dependent effects were more likely to occur with emotional text or story materialsand much less likely to occur with list materials, even lists containing positive and neg-ative words. Further, Riskind stated that mood-congruency effects tended to occurunder the precise conditions that were often used to create mood state-dependencyeffects. He explained this using his “cognitive-priming formulation,” which statedthat the cognitive system employs “preexisting schemas or categories in learningand retrieving information” (Riskind, 1989, p. 178). The use of these schemas placespriority on the learning episode, emphasizing “interactive encoding” (Riskind, 1989,p. 182) and resulting in the pattern of results found in mood and memory research.

Mood-congruent memory, compared to mood state dependence, has a strongrecord of replicability. In fact, mood-congruity effects have even been found in theabsence of mood (Perrig & Perrig, 1988)! For the purposes of the current review, itis important to note that the search for any effect of depression on implicit memorycenters around Bower’s (1981) concept of mood-congruent memory (MCM). In thiscontext, the material to be remembered must have some emotional valence. Further,it should be noted that MCM effects actually require that the pattern of results be re-versed for depressed participants and controls, with depressed participants showingenhanced memory for negative words, and controls showing enhanced memory for

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positive words. Three studies have delved into depression and implicit memory since1990, but without using emotionally valenced stimuli (Danion et al., 1991; Hertel& Hardin, 1990; Jenkins & McDowall, 2001). Because they do not meet the crite-ria necessary to detect MCM bias, they are not included in this review. With this inmind, then, the literature on the effects of depression on implicit memory is exam-ined. Tables II and III present the data to be reviewed in tabular form, noting theimportant elements and findings of each study. Table II presents studies finding noeffect of depression on implicit memory, whereas Table III presents studies findingan effect of depression on implicit memory. The studies presented in these two tablesappear in chronological order for ease of reference. Also, as noted earlier, the litera-ture to be reviewed differs across many different dimensions, including participants,tasks, and methodology, further supporting the appropriateness of a chronologicalpresentation for each table. Finally, because participant populations in these studiesdiffer along various dimensions as noted previously, hereafter participant groups willbe referred to as “participants classified as depressed,” or “depressed participants”and “nondepressed participants” or “controls.”

Studies Finding No Effect of Depression on Implicit Memory

Early experiments often failed to find an effect of depression on implicit memory(Bazin et al., 1994, 1996; Danion et al., 1995; Denny & Hunt, 1992; Ilsley et al., 1995;Lang & Craske, 1997; Watkins et al., 1992). A brief summary of these experimentsappearing in Table II will help to understand the methods and subsequent conclusionsof each.

First, Denny and Hunt (1992) hypothesized that a dissociation between perfor-mance on an explicit and an implicit task would provide evidence for an impairmentof effort-demanding processing in depressed participants (the explicit free recall task)compared with an “automatic” implicit memory task. This study appears in Table II.Clinically depressed individuals were matched with controls and both groups weregiven implicit and explicit memory tests. Each participant was given a list containingpositively and negatively valenced words, which they rated according to the words’relevance to themselves (i.e., a self-reference orienting task). Denny and Hunt thenhad participants perform a word fragment completion task and a free recall task(order of tests was counterbalanced across conditions). Although the data seemedto indicate a trend for enhanced priming for depressed participants’ negative words(what amounts to a depressive bias), the differences were not statistically significant.Depressed participants did recall significantly fewer words in the free recall task, andthe pattern of results indicated an MCM bias. Thus, the authors concluded that therewas no differential effect of word valence by participant group (no MCM bias) onthe implicit memory task.

Table II shows that at the same time the Denny and Hunt (1992) paper waspublished, Watkins et al. (1992) used clinically depressed participants and nonde-pressed controls, testing them with both implicit and explicit memory tasks. Theauthors’ choice of participants was driven by the same underlying reasoning as in theDenny and Hunt (1990) study described above. Word lists consisted of positively andnegatively valenced emotional words. Negative words included depression-related

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Tabl

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Tabl

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and physical-threat words. Each word was presented for 10-s and participants wereasked to form images of themselves interacting with the word. There was a significantMCM bias found in free recall for negative words. Interestingly, this was only true fordepression-related words—control participants recalled more physical-threat wordsthan depressed participants did. Also, similar to the previously discussed paper, therewas a trend in the data toward MCM bias in the word stem completion task for neg-atively valenced words by depressed participants. Again, however, the differencewas not reliable and Watkins et al. (1992) concluded that there was no evidence ofdepressive MCM bias in implicit memory.

Bazin et al. (1994) presented implicit and explicit memory tasks to both clinicallydepressed (hospitalized) patients and non-depressed controls as noted in Table II.These authors sought to provide evidence that the dissociations between explicitmemory and implicit memory in depressed patients as reported in previous studieswere not due to differences in the available cues for each type of test. Participantswere informed that their memory would be tested, and they were presented withemotionally valenced words which they read aloud. An implicit word stem comple-tion task and an explicit cued recall task followed, using the same stems as cues asin the implicit test. Thus, the materials to test implicit and explicit memory were thesame, and only the instructions differed in this study. As in the previous two experi-ments, a nonsignificant trend toward MCM bias in depressed patients for the implicitmemory task appeared. There was no MCM bias in the cued recall task, althoughcontrols had higher recall scores. Once again, Bazin et al. (1994) concluded that theperformance of depressed patients and controls did not differ on the implicit memorytask. Interestingly, the authors also tested participants at the end of their hospitaliza-tion, when they had made “clinical improvement” (p. 243). This time, the dissociationin recall between patients and controls disappeared, supporting the notion that it isthe depressive disorder itself that is responsible for the previous differences found inexplicit memory, and not any confounds resulting from using a hospitalized sampleand a nonclinical control group.

In the next study to appear in the literature and in Table II, Danion et al. (1995)tested clinically depressed inpatients versus controls on both implicit and explicitmemory tasks. They hypothesized that depressed patients would demonstrate a prob-lem with elaboration (a conscious process that requires effort), a deficit that wouldappear on an explicit memory task. As in the other studies reviewed in this section,these authors predicted no differences in a more automatic (implicit memory) task.Using emotionally valenced words, they instructed participants to try to rememberthe words. Participants were given 5-s to read each word aloud and rate its pleas-antness on an analogue scale. Memory was then tested by a word completion task,followed by a free recall task and a recognition task. No MCM bias was found on theimplicit memory task. Results of the two explicit tasks, however, were quite unusual.Depressed participants recalled significantly more negative than neutral words, butalso significantly more positive than neutral words. Control participants, on the otherhand, recalled significantly more positive than neutral words, and more negative thanneutral words although this latter difference was not significant. Overall recall didnot differ between the two groups. Results of the recognition task were similar tothe recall task. The authors concluded that “the affective valence of words influences

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memory when conscious intentional recollection is required but is devoid of effecton memory when such recollection is not required” (p. 233).

As shown in Table II, Ilsley et al. (1995) subjected clinically depressed patientsand non-depressed controls to a battery of tests, which included implicit and ex-plicit memory measures. Some of their depressed patients were also psychotic. Thehypotheses of this study were that semantic memory (tested by an implicit task)would “be largely intact in depression” (p. 3), whereas these depressed participantswould show an impairment of explicit memory. Without knowing their memory wouldbe tested, participants were presented with emotionally valenced words and askedto evaluate the extent to which each of these words described themselves (i.e., aself-referencing task). Participants then performed a word completion test followedby a cued recall test. As in the previously described research, no significant dif-ferences were found between participant groups on the word-completion task. In-terestingly, there were also no group differences on the cued recall task, failing tosupport the authors’ hypothesis regarding explicit memory. The authors offered noinsight as to why this might have been the case, they simply speculated that “this[MCM bias] is not as robust and replicable a phenomenon as is widely believed”(p. 8).

Bazin et al. (1996) examined depressed patients, schizophrenic patients, and non-depressed controls, as noted in Table II. They hypothesized that MCM bias wouldonly appear for depressed patients in the explicit recall task, and would disappearwhen the patients recovered. Using both implicit and explicit memory tasks, theyinstructed participants to read the words out loud and to expect a memory test.The words were emotionally valenced common words. In the subsequent word stemcompletion task, Bazin et al. (1996) found no significant differences in the number ortypes of word stems completed by the three groups. The authors also failed to find asignificant difference in cued recall. In fact, both controls and depressed participantsrecalled significantly more negative words than positive words, failing to demonstratethe MCM bias the authors had hypothesized. The results were the same for depressedrecovered patients and controls.

Finally, using physically and socially threatening words as stimuli, Lang andCraske (1997) examined nonclinically anxious and depressed participants on explicitand implicit memory tasks. Participant groups were low depression and low anxiety,low depression and high anxiety, and high depression and high anxiety. Lang andCraske instructed participants to read sentences and determine whether or not thetarget word made meaningful sense. Afterward, participants completed a free recalltask and then a word stem completion task. Statistical analysis did not detect anyreliable differences in priming of negative words by depressive status. In other words,no MCM bias was found with the socially threatening for individuals characterizedwith high depression. An important consideration, however, when evaluating thisstudy is the authors’ use of the free recall task (explicit) prior to the word stemcompletion task (implicit). Virtually all of the research on implicit memory testsimplicit memory first and then explicit memory to avoid contamination. Thus, inaddition to the argument promoted by the current paper, it is not surprising that noMCM bias was found in the Lang and Craske (1997) study. Despite this serious designflaw, the study was included in the current review because of its MCM elements.

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Without exception, at least for the earlier studies reviewed above and appearingin Table II, depression had no consistent effect on implicit memory. Each of thesestudies used a perceptual implicit memory task (word stem completion or wordfragment completion). However, as will be seen in the next section, the choice oftask alone cannot account for the failure to find significant differences in implicitmemory by participants classified as depressed and controls.

Studies Finding an Effect of Depression on Implicit Memory

More recent research, however, has rather consistently found that depressiondoes affect implicit memory (Bradley et al., 1994, 1995, 1996, Expts. 1 and 2:Ruiz-Caballero & Gonzalez, 1994, Expts. 1 and 2; Ruiz-Caballero & Gonzalez, 1997;Watkins et al., 1996). As in the previous section, a brief summary of these experi-ments appearing in Table III will help to understand the methods and subsequentconclusions of each.

For example, as can be seen in Table III, Bradley et al. (1994) investigated bothimplicit and explicit memory for emotional and neutral words using a nonclinical re-search sample. To test two different theories with opposite predictions, they presentedparticipants with both supraliminal (the participant was aware of its presentation) andsubliminal (presented too briefly for conscious awareness) primes. They then useda lexical decision task to determine the amount of priming produced under theseconditions. Interestingly, when compared to a low negative affect group, participantswho scored high on measures of negative affect (the State Trait Anxiety Inventoryand the Beck Depression Inventory) showed increased priming for subliminally pre-sented depression-relevant words compared to neutral words. In contrast, there wasno enhanced supraliminal priming for high negative affect participants comparedto low negative affect participants. Using the automatic/nonautomatic distinction ofMandler (e.g., 1989), Bradley et al. interpreted the depression-congruent primingeffect as evidence that subliminal priming is due to a depressive bias in automatic,integrative processes of high negative affect individuals. On the other hand, supral-iminal priming allows for strategic processing, which can be used by non-clinical highnegative affect participants to compensate for their depressive bias. The authors ofthis study went so far as to say that the study provides “consistent significant evi-dence of a depression-congruent bias in automatic memory processes, as reflectedby subliminal priming effects” (pp. 75–76).

In the same year, and also appearing in Table III, Ruiz-Caballero and Gon-zalez (1994) also used “depressed” versus “nondepressed” student volunteers andseparated the two groups according to their scores on the Beck Depression Inven-tory (BDI). This particular sample was used to determine if any MCM bias wouldappear in “subclinically depressed Ss” (p. 557). Under intentional encoding instruc-tions for Experiment 1, participants were presented with positively and negativelyvalenced words. Afterward, they performed a word stem completion task, consti-tuting the implicit memory test, and a free recall test of explicit memory. Results ofthe study indicated that there was an MCM effect for explicit memory, and that the“depressed” participants also showed more priming of negative words. To ensurethat participants were not using explicit strategies to help them complete the word

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stems, Ruiz-Caballero and Gonzalez performed a second experiment. To eliminatethe possible influence of explicit strategies being used during an implicit memory task,Ruiz-Caballero and Gonzalez provided half of their participants with intentional en-coding conditions, and half of their participants with incidental-physical encodingconditions. For the former condition, participants were told that their memory forthe words would be tested. For the latter condition, participants were instructed tocount the number of vowels in each word as quickly as they could. Results indicatedthat once again, “depressed” participants showed a larger priming effect on the wordcompletion task for words of negative valence. Importantly, this effect was not dif-ferent for intentional versus incidental learning conditions. Contrary to the earlierresearch reviewed, the authors concluded that “if memory bias is assessed from theease with which a representation of an emotional word can be accessed once it hasbeen primed (implicit memory), the present research also provides evidence thatdepressed and nondepressed Ss do indeed show a bias favouring emotional infor-mation” (p. 566). Ruiz-Caballero and Gonzalez interpreted their results in terms ofBower’s (1981) network model of mood and memory.

In a companion to their 1994 study, Bradley et al. (1995) examined implicit andexplicit memory for emotional information, using clinical populations of chronicallydepressed and clinically anxious participants. This study is also summarized in Ta-ble III. Their purpose was twofold: to include anxious participants in addition to de-pressed participants, and to find differences between anxious and depressed patientson implicit tasks. Using the same type of materials as in their former study (Bradleyet al. 1994), and contrary to their hypothesis, they found that depressed participantsshowed cognitive MCM bias on three types of memory tasks: implicit tasks comprisedof both subliminal priming and supraliminal priming, and an explicit memory task(free recall). Bradley et al. (1995) suggested that both automatic and strategic pro-cesses are consistently biased in depressed participants toward depression-relevantinformation.

To round out their series of experiments, Bradley et al. (1996) conducted twoadditional experiments, in which they combined features of each of their studiesdiscussed above. Because of their design differences, these experiments are listedseparately in Table III. In Experiment 1, Bradley et al. (1996) hypothesized thatdysphoric individuals would show less priming for neutral words than for depressionwords, in comparison with nondysphoric individuals, especially in the subliminalcondition. Their results supported this hypothesis, showing subliminal priming ofdepression-related words by non-clinical dysphoric participants. In Experiment 2,they hypothesized that clinically depressed individuals would show the same pat-tern of results as the dysphoric individuals from Experiment 1. In addition, theypredicted that the enhanced priming of depression-related words by depressed in-dividuals would also extend to supraliminal priming. Bradley et al. (1996) foundenhanced subliminal priming and supraliminal priming of depression-related wordsin clinically depressed participants. Together, these results replicated their previousfindings, and they concluded, “[e]vidence of depression-congruent effects in auto-matic memory processes seems more consistent with the schema and network the-ories considered earlier . . . ” (p. 877). Bradley et al. (1996) pointed out, however,that the important perceptual/conceptual distinction of Tulving and Schacter (1990)needed to be considered in future studies of depression and implicit memory. In other

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words, because certain implicit tasks rely on perceptual priming, whereas others relyon conceptual priming, this distinction needs to be experimentally manipulated withregard to depressed participants. Further, Bradley et al. noted that purely percep-tual priming implicit memory tasks may mask possible mood-congruent effects ifthe perceptual priming effects are masking “emotion-congruent priming effects”(p. 877).

Apparently unaware of the research just reviewed, Watkins et al. (1996) used aconceptual implicit memory test to measure mood-congruent bias in depression. Asnoted in Table III, they selected clinically depressed individuals and contrasted themwith non-depressed controls, hypothesizing that MCM bias would be demonstratedusing a word association implicit memory task. Their prediction follows logicallyfrom the Transfer Appropriate Processing framework (which is similar to the Bowermodel and is discussed in the next section), which they pitted against the elaborationhypothesis of Williams et al. (1988). Without citing any of the studies discussed above,Watkins et al. (1996) claimed to be the first authors to find an implicit mood congruentmemory (MCM) bias in clinical depression. They first presented participants withpositive, neutral, and negative words and instructed them to imagine themselves in ascene that involved the word for 15-s. Watkins et al. (1996) then provided participantswith a conceptual implicit memory test. Specifically, they provided participants witha series of association cues to which they were to respond with as many associatesto each as they could. This continued for 30-s per cue. In fact, these authors diddemonstrate MCM bias by their clinically depressed participants. That is, depressedparticipants provided more studied negative words in response to association cuesthan did controls and controls provided more studied positive words in response toassociation cues than did depressed participants. These authors concluded that theirresults were “consistent with the spreading activation approach of Bower (1981) andthe schema theory of Beck” (p. 39).

Finally appearing in Table III, non-clinically depressed and non-depressed par-ticipants were studied by Ruiz-Caballero and Gonzalez (1997). They assessed theeffects of semantic versus nonsemantic processing (a conceptual vs. perceptual levels-of-processing distinction) on implicit memory in their participant population, hypoth-esizing that this manipulation would have no effect on implicit task performance, butwould have an effect on explicit task performance. Under the semantic (conceptual)processing condition, and to encourage elaborative processing, participants were in-formed that their memory would be tested and then were presented with emotionallyvalenced words that they rated on a Likert scale for pleasantness. Nonsemantic (per-ceptual) processing instructions did not inform participants that their memory wouldbe tested, and then presented them with emotionally valenced words for which theywere to perform a letter counting task. All participants were then given a word stemcompletion task followed by a free recall test. Results indicated that there was alarger priming effect for mood-congruent words than for words that were not mood-congruent. Ruiz-Caballero and Gonzalez (1997) also found an MCM effect in freerecall. The authors suggested that mood-congruent information is more accessiblethan mood-incongruent information, consistent with Bower’s (1981) network theoryof emotion.

Each of the studies just discussed and presented in Table III used a perceptualimplicit memory task (word stem completion and lexical decision), with the exception

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of the Watkins et al. (1996) study, which used a conceptual implicit memory task(word association). Because the research reviewed in the previous section (studiesfinding no effect of depression on implicit memory) also included perceptual implicitmemory tasks, as concluded in the preceding section, the nature of the implicit taskalone does not seem to explain the equivocal nature of the results of empirical studiesof the effect of depression on implicit memory. What other factor might account forthese differential results?

WHY THE EQUIVOCAL RESULTS IN THE LITERATURE?

Aside from the methodological differences in the studies described above, thereis one other explanation that successfully accounts for the inconsistent results in theliterature on implicit memory and depression. Because the research focuses on moodcongruent memory (MCM), the learning episode and its conditions are often held tobe most important in determining whether there might be an implicit MCM bias indepression. However, it is our contention that the testing episode and its conditionsare also important. To provide support for this standpoint, first, the tasks used totest implicit memory biases will be examined. Next, a framework for conceptualizingboth the learning and testing episodes will be examined.

Nature of the Tasks

Earlier, the theoretical distinction between conceptual and perceptual implicitmemory tasks was mentioned. This issue returns the focus to the testing episode,which is less important in traditional mood congruent memory research. In gen-eral, conceptual tests refer to those types of memory tests in which performancebenefits from elaborative manipulations (i.e., generating information, semantic pro-cessing, etc.). They are often considered to involve cognitive effort. Perceptual tests,on the other hand, refer to memory tests that depend upon the match of perceptualprocessing between study and test, and that seem to test a perceptual record of apast experience (like word stem completion, or subliminal priming). Compared withconceptual tests, perceptual tests are often considered to require very little, if any,cognitive effort. Although explicit tests are usually thought of as conceptual tests,and implicit tests are usually thought of as perceptual tests, Roediger et al. (1989)have long argued that dissociations can be found even within implicit tests (see alsoBlaxton, 1989; Tulving & Schacter, 1990). They provide evidence that there is not anecessary correlation between implicit memory tests and perceptual processing, andshow that it is possible to construct both conceptual and perceptual implicit memorytests. That is, each type of test taps a unique process in implicit memory—implicitmemory is not merely a way of describing perceptual processing without awareness.Further, Roediger et al. postulate a continuum of implicit tests, characterized bythose requiring primarily meaning-based information (conceptual) or primarily per-ceptual information. For these researchers, word stem completion, word fragmentcompletion, and lexical decision tests all can be described as primarily perceptualtests. Tasks like word production or generating words from meaning clues wouldrepresent primarily conceptual tests.

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It can be argued, however, that neither word-stem completion nor repetitionpriming tasks using depression-related stimulus words represent solely perceptualpriming tests as described by Roediger et al. (1989). First, the use of depression-related words necessarily imposes meaning on a portion of the stimulus words,making the categorical nature of the test materials obvious. Second, according toRoediger and McDermott’s (1992) commentary (Table 1, p. 588), there appears tobe a dissociation between the performance of depressed participants and controls onimplicit memory tasks. Specifically, for both word fragment completion (Denny &Hunt, 1992) and word stem completion (Watkins et al., 1992) the pattern of resultsfor priming scores of positive words and negative words (depression-related words)is reversed for depressed participants relative to controls. In other words, controlparticipants demonstrated enhanced priming for positive words, whereas depressedparticipants demonstrated enhanced priming for negative words. Even though thesedifferences were not statistically significant, they were consistent. This finding maysuggest that meaning is a central component to some implicit memory tasks, possiblyremoving them from the perceptual end of the continuum.

Finally, even studies that show no influence of depression on implicit tasks (Bazinet al., 1994; Danion et al., 1995; Denny & Hunt, 1992) show a trend toward increasedresponding by depressed participants for negative words. These results fit in verywell with the idea of a continuum of implicit memory tests. In this case, the implicittasks used in the studies reviewed above may not truly be perceptual tasks. Thatis, the automatic and conscious (controlled) aspects of perceptual and conceptualtasks (respectively) may be responsible for the inconsistent findings in the literatureregarding the effects of depression on implicit memory. It also may be the case thatfor tasks not purely perceptual in nature, nonsignificant findings (showing a “trend”toward MCM bias) would sometimes be expected to occur, especially in studies withsmall samples such as the research reviewed here (Denny & Hunt, 1992; Watkinset al., 1992). It is also expected that significant differences in memory performancewould sometimes be found, even in rather small samples (Bradley et al., 1995; Watkinset al., 1996). The four implicit memory tasks described in Table 1 were presentedin order from the most perceptual (lexical decision) to the most conceptual (wordassociation), reflecting this notion of a continuum of implicit memory tasks.

Transfer Appropriate Processing

Definition

The idea of a continuum of tasks is further complicated by processing considera-tions. Roediger and Blaxton (1987) discussed processing distinctions in terms of their“Transfer Appropriate Processing” (TAP) framework. They argued against the pop-ular multiple memory systems framework (e.g., Schacter, 1987; Sherry & Schacter,1987) and explained dissociations between explicit and implicit memory in termsof the different processing requirements for the two types of memory. Accordingto their view, it is the match between the type of processing requested at encoding(study or learning) and the type of processing required at retrieval (test or task) thatis important and not the activated “memory system” itself that is the definitive factor

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in determining what is remembered. In other words, is there a match in processingrequirements between the study task and the testing task? If so, better performanceis expected on the testing task, reflecting facilitated cognitive performance, or bettermemory. Recall that studies of mood congruence tend to focus on the study or learn-ing episode, and place less importance on the characteristics of the testing episode.

Roediger and Blaxton’s (1987) presentation of TAP is similar to Tulving andThompson’s (1973) Encoding Specificity Principle, and indeed encoding specificity isone of the foundational elements of TAP. The second foundational element of TAPis that different tests of memory result in different mental operations for performingthe tests. For this reason, the types of mental operations required may vary accord-ing to which test is administered. Roediger and Blaxton’s main premise, then, is thatsemantic memory is usually tested perceptually and is often what we think of astesting “implicit memory,” whereas episodic memory is usually tested conceptuallyand is often what we think of as testing “explicit memory.” The assumption is oftenthat implicit memory relies on automatic processing, whereas explicit memory relieson controlled processing. This belief probably stems from the extensive literaturewhich shows encoding manipulations that traditionally produce obvious effects onexplicit memory tests often do not affect performance on implicit memory tests. Intheir review of this literature, Richardson-Klavehn and Bjork (1988) described re-search studies which demonstrated that the variables levels of processing, amountof elaborative processing, difficulty of encoding, and amount of study time all failedto affect the amount of priming during a later perceptual identification task. Suchfindings are suggestive of the role of automatic processing in implicit memory tests.That is, variables that affect explicit memory but not implicit memory are thought tobe variables that do not rely extensively on automatic processing. Further, some de-velopmental research has also failed to find age differences in the amount of primingobserved on implicit memory tests (e.g,. Drummey & Newcombe, 1995; Greenbaum& Graf, 1989; Naito, 1990; Parkin & Streete, 1988). If priming is conceptualized as re-quiring automatic processing, these findings could be accurately predicted by Hasherand Zacks’ framework of automatic and effortful (controlled) processes in memory(Hasher and Zacks, 1979), which states that automatic processing appears early inlife and changes little during development.

In addition, Laird Cermak and his colleagues have studied the implicit mem-ory of clinical patients (Korsakoffs, alcoholics, and controls) for over a decade (e.g.,Cermak, 1993). These studies built upon earlier work on explicit memory in thispopulation (e.g., Cermak, Naus, & Reale, 1976; Naus, Cermak, & DeLuca, 1977). Inpart, Cermak’s more recent investigations into the nature of amnesics’ memory havefocused on the notion of perceptual versus conceptual priming. Specifically, Cermak(1993) designed experiments based on Blaxton’s (1989) and Roediger’s (1990) no-tions of perceptual and conceptual processing in implicit memory tasks to examinethe range of processing abilities of his clinical population. Although it is well knownin the cognitive literature that even people with severe amnesia demonstrate nor-mal implicit memory performance, this finding does not necessarily mean that theyhave an “intact” implicit memory. By realizing that “amnesics’ normal implicit per-formance is not always a consequence of normal processing,” Cermak (1993, p. 288)was able to experimentally separate the two types of processing. He concluded that

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amnesic patients may perform normally on implicit memory tasks because such taskstend to require automatic perceptual processing. These same individuals may exhibitdeficits on explicit memory tasks because such tasks tend to require strategic con-ceptual (controlled) processing, which may no longer be available to them. Thus,it is not the memory system per se (e.g., implicit memory) that is preserved in am-nesic patients, rather it is the type of processing (e.g., perceptual, relying on auto-maticity) that is usually required in implicit memory tests that is preserved in thatpopulation.

In this paper, we are maintaining the premises of TAP while disregarding thenotion of memory systems. Thus, it is our contention that ultimately it is the type ofprocessing that is the most important factor with regard to memory, over and aboveany memory systems that may exist, and beyond merely the type of test. Thus, follow-ing Roediger et al. (1989), we posit that there are both conceptual and perceptual testsof implicit memory. The seemingly inconsistent nature of the research on depressionand implicit memory discussed herein can be explained in terms of this TAP frame-work. When the TAP framework is applied to the types of study/test conditions ofthe research on implicit memory and depression reviewed herein, an important pat-tern emerges. Specifically, processing requirements of encoding (study) and retrieval(test) contexts influence how well or poorly depressed and non-depressed individualsperform on mood-congruent material. In support of this argument, Watkins (2002)reviewed a decade’s worth of work in his own laboratory exploring MCM biases indepression. Using a chronological organizational approach, he attempted to showthe necessity of conceptual processing at both study and test to reveal implicit mem-ory bias. After examining his own published and unpublished studies on the subject,he concluded that conceptual processing is a necessary, but not sufficient conditionfor showing implicit memory bias in depression.

TAP Applied to Depression and Implicit Memory

All of the studies investigating implicit memory and depression that are pre-sented in Tables II and III can be reconceptualized using a TAP framework. A simi-lar approach has recently been presented by Barry and Naus (2001) to organize andreview the extant literature on the development of implicit memory in children. Ap-plying the TAP framework involves an investigation of processing demands duringthe study episode in concert with the processing demands of the test episode. Whensuch an approach is used, all of the studies reviewed above and summarized in Ta-ble III (in which a mood-congruency bias in implicit memory was found for depressedparticipants), were designed in such a way that the processing demands during en-coding were perfectly matched to the processing demands during testing. That is,each of the empirical studies under the section “case for the effect of depression onimplicit memory” used “shallow,” or perceptual, encoding conditions and a task thatdemanded perceptual processing. The only exceptions to this were the Watkins et al.(1996) and the Watkins, Martin, & Stern (2000) studies listed in Table III, which used“deep,” or conceptual, encoding conditions combined with a task that required con-ceptual processing. This combination, however, still represents a match of processingdemands, albeit not perceptual. Conversely, the empirical studies under the section

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Table IV. Implicit Memory and Depression Research Studies by Encoding (Study) and Retrieval (Test)Conditions

Encoding task

Testing task Nonsemantic (perceptual) Semantic (conceptual)

Perceptual Ruiz-Caballero and Gonzalez (1997)a Ruiz-Caballero & Gonzales (1997)a

Bradley, Mogg, and Millar (1996), Expt. 1a Ilsley et al. (1995)Bradley, Mogg, and Millar (1996), Expt. 2a Danion et al. (1995)Bradley, Mogg, and Williams (1995)a Watkins et al. (1992)Ruiz-Caballero and Gonzales (1994), Expt. 1a Denny and Hunt (1992)Bradley, Mogg, and Williams (1994)a

Bazin et al. (1996)Bazin et al. (1994)Watkins, et al. (2000)

Conceptual Watkins, et al. (2000) Watkins et al. (2000)a

Watkins, et al. (1996)a

aIndicates studies which found significant MCM bias in implicit memory.

“case against the effect of depression on implicit memory” primarily used “deep”encoding conditions and a task that demanded perceptual processing.

Table IV therefore presents the same experiments on depression and implicitmemory as Tables II and III, but reorganized into one of four possible cells cre-ated by the TAP framework. Orthogonally crossing the processing required at bothstudy and at test, four distinct combinations of study (perceptual or conceptual) andtest (perceptual or conceptual) are formed. The resulting categories are perceptualstudy/perceptual test, perceptual study/conceptual test, conceptual study/perceptualtest, and conceptual study/conceptual test. A reexamination of the studies presentedin Tables II and III according to their study/test processing demands reveals a theoret-ically important pattern of implicit memory results. The studies that were designedwith a match of perceptual (shallow, or nonsemantic) encoding conditions pairedwith a perceptual test overwhelmingly find an implicit MCM bias. Conversely, thosestudies that contained a “mismatch” of conceptual (deep, or semantic) encoding con-ditions paired with a perceptual test overwhelmingly failed to find an implicit MCMbias. Table IV also makes it very clear that only two of these studies utilized a concep-tual implicit memory test (Watkins et al., 1996, 2000). In these studies, the conceptualimplicit memory test was preceded by conceptual encoding conditions, constitutinga “match” of conceptual study/conceptual test. Under these “match” conditions, theWatkins et al. (1996) and the Watkins et al. (2000) studies found implicit MCM bias.An extrapolation of the findings presented in Table IV seems to suggest that implicitMCM bias might be expected when there is a match between processing demandsduring study and test of implicit memory (like the perceptual study/perceptual testcell in Table IV).

Support for the Framework

A similar approach toward understanding implicit memory and depression wasrecently investigated by Watkins et al. (2000). They empirically investigated mood-congruent memory bias in depression by using two perceptual memory tests (word

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stem completion and word identification) and two conceptual implicit memory tests(free association and word retrieval). Although these authors also performed testsof explicit memory, no results were reported for those tests. The Watkins et al. (2000)study is also represented in Table IV.

Using the TAP framework, Watkins et al. (2000) manipulated encoding condi-tions as well as implicit memory tests, and used positive and negative adjectives asstimuli words for their sample of clinically depressed participants and non-depressedcontrols. Perceptual encoding was achieved by having participants count the numberof ascending and descending letters in presented words. For conceptual encoding,participants responded on a 9-item Likert scale as to when they last experiencedsomething related to the word (from “right now” to “never”). Preliminary analyseswere performed to ensure that priming was effective across implicit tests, and thatdepth of processing indicated that the conceptual tests were more conceptual thanthe perceptual tests. Priming scores were computed by simply subtracting completionrates of unstudied words from those of studied words. Separate analyses of variancewere then performed on perceptually encoded and conceptually encoded words.

Watkins et al. (2000) found that there was no evidence of MCM bias with theperceptually-encoded words, and so reported no further results for them. Analysisof conceptually-encoded words revealed that MCM bias differed by implicit test.Specifically, MCM effects were found only for the word retrieval test, and only forthose words that were encoded conceptually. Watkins et al. (2000) concluded thatusing conceptually driven tests are a necessary but not sufficient condition for find-ing MCM in depression. Interpretation of the results was done through both theinteractive cognitive subsystems approach of Teasdale and Barnard (1993) and thecognitive model of Williams et al. (1997). Thus, the Watkins et al. (2000) study wouldappear to support the current proposal, at least in part.

Despite this partial support for the TAP framework applied to implicit memoryand depression, however, there are several important limitations to the Watkins et al.(2000) study. First, although they report finding negative priming of perceptually-encoded words by controls, they offer no possible explanation. Interestingly, bothconceptual tests showed negative priming by controls when the words were percep-tually encoded. This means that for the free association test, as well as the wordretrieval test, control participants reported fewer studied words than unstudied forthose words in which they counted ascending and descending letters. This negativepriming occurred for both positive and negative words. Because negative priming isusually explained in terms of attentional differences (e.g., Williams et al., 1997), it isnot surprising that these authors failed to direct their attention to this anomaly.

Second, Watkins et al. (2000) used a “raw” index of priming, whereby they sim-ply subtracted the proportion of unstudied words completed from studied wordscompleted. Further, for the purposes of analysis of variance, priming scores werenot entered into calculations; raw percentages of studied and unstudied words com-pleted were used. Priming scores alone (separated from completion rates) representa dependent measure that is more representative of the variable of interest, assur-ing an analysis of the priming effect resulting from the manipulation unconfoundedwith baseline completion rates. For a discussion of the merits of a “raw” index ofpriming versus a “relative” priming index, especially when baseline completion rates

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Table V. Representation of the Data From Watkins, Martin, and Stern (2000)

Encoding task

Perceptual (Priming index) Conceptual (Priming index)

Testing task Raw Relative Raw Relative

PerceptualDepressed

Positive 5.74 .09a 12.87 .20Negative 7.56 .12a 9.40 .15

ControlsPositive 8.65 .14a 13.12 .21Negative 4.25 .08a 11.58 .19

ConceptualDepressed

Positive 2.94 .05 7.07 .13a

Negative 4.88 .09 13.20 .22a

ControlsPositive −1.72 −.03 15.19 .29a

Negative −1.16 −.02 9.60 .16a

aIndicates where a pattern of MCM bias can be seen.

differ among sample groups (here by depressive status, word valence, and test), seeSnodgrass (1989).

Third, the design of the statistical analyses probably served to wash out some ofthe possible MCM effects. Perceptually-encoded and conceptually-encoded wordswere analyzed separately, even though they were specifically included in the exper-iment to evaluate the TAP framework. Analyzing these two conditions separatelyfrom each other is the most conservative type of test possible in this study. In fact, ifpriming scores were calculated and the entire design analyzed together, the resultsmight have been very different. In this spirit, a rough attempt is made here, recog-nizing that it is only an estimate of the data due to lack of having the raw, individualscores to work from. Table V presents both raw and relative priming indices, calcu-lated from Table 1 of the Watkins et al. (2000) study. In Table V, the two perceptualtests and the two conceptual tests were averaged together for ease in presentation,although keeping them separate retained the same pattern of results. Although nostatistical analyses were performed on the data presented in Table V, a pattern ofresults can clearly be seen that indicates MCM bias in depression under conditionswhere processing demands are matched. In particular, priming scores are reversed indirection by word valence for depressed participants and controls in the perceptualstudy/perceptual test and the conceptual study/conceptual test quadrants. That is, de-pressed participants showed more priming for negative words, and controls showedmore priming for positive words in these two quadrants. This reanalysis, althoughonly an estimate, clearly supports TAP and our current model in its predictions.Watkins (2002) himself also noted these MCM patterns in this study in his discussionof processing considerations in implicit memory and depression.

As alluded to earlier, Hasher and Zacks (1979) first suggested that automaticand effortful memory processes are differentiable in terms of their encoding oper-ations. They proposed that effortful processes were affected by variables such as

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development, aging, depression, and arousal. These same variables, notably, did notseem to influence automatic processes. However, this groundbreaking processingframework tells only half of the story. The current discussion of processing demandsin combination with testing demands (TAP) tells a more complete tale. For example,it is when the processing demands do not match that developmental differences inmemory performance may be found (Barry & Naus, 2001). In other words, underconditions of perceptual study/perceptual test of implicit memory, even young chil-dren can perform quite well compared to adults. When conditions require conceptualstudy/perceptual test, however, decrements in the implicit memory performance ofchildren are seen relative to adults. In the developmental case, automatic process-ing appears early in development and remains fairly stable throughout the lifespan,per Hasher and Zacks (1979; for empirical examples see Graf, 1990; Parkin, 1993;Sommers, 1999). This assures good performance on implicit memory tests that re-quire perceptual processing, even by children. When task demands require differenttypes of processing (like a conceptual implicit memory test), children no longer areassured good performance because their controlled, strategic processing abilities arestill developing.

In the current discussion of depression, the cognitive processing by participantsclassified as depressed can be thought of in much the same way as the developingchild’s—the automatic, perceptual processing abilities remain intact and relativelyunaffected by depression, whereas the conceptual, strategic processing abilities areaffected by the presence of depression. In this way, the compromised processingability of the depressed person is similar to the child’s “comprised” processing abilityrelative to an adult. The similarities between these two very different populationswith regard to implicit memory findings is strong support for the TAP framework,underscoring the importance of processing considerations in understanding implicitmemory.

CONCLUSION

During the last two decades of the twentieth century, memory research in cog-nitive psychology was characterized by the study of implicit memory. This interesthas also extended into depression research, just as clinical psychologists have in-creasingly used cognitive theories to explore and explain depression. The researchstudies reviewed in this paper highlight several important points regarding implicitmemory. First, the literature on implicit memory and depression is widely discrepantwith respect to methodology, design, and participant samples. Second, this literatureis inconsistent in its findings of the effect of depression on implicit memory. Approx-imately half of the studies demonstrated no mood congruent bias in implicit memoryby depressed participants, whereas the other half of studies managed to find such abias. Third, when reconceptualized into the Transfer Appropriate Processing (TAP)framework of memory, the research studies fall into a theoretically important patternof results for future considerations to memory models of emotion. Fourth, the resultsshowing the importance of matching processing demands during encoding (study)and retrieval (test) emphasize the role of processing considerations in understanding

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memory phenomena. These considerations are especially important in decipheringthe literature on the effect of depression on implicit memory.

Although many important inroads into the understanding of depression andimplicit memory have been made, it is clear that there is much more work to be done.The Transfer Appropriate Processing organizational scheme (as set out in Table IVherein) is important for future studies of depression and implicit memory, from whichit is possible to generate testable hypotheses regarding the nature of depression andimplicit memory. Further, notions of treatment for depressed individuals may beaffected as well, as new ways of understanding mood congruent memory biasesemerge. In addition, implicit memory findings will lead to the reformulation and/orexpansion of many of the current memory models of emotion (e.g., Rehm & Naus,1990; Riskind, 1989; Williams et al., 1997).

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