ABSTRACT. BRATTON, KEVIN M. Thought Suppression: Divergent Implications for Explicit and Implicit Memory. (Under the direction of Katherine W. Klein.

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1 ABSTRACT BRATTON, KEVIN M. Thought Suppression: Divergent Implications for Explicit and Implicit Memory. (Under the direction of Katherine W. Klein.) The purpose of this research was to examine the relationship between suppression of a personal negative experience and performance on a task that included an explicit or recollection component, and an implicit or familiarity memory component. The study was a 2 (study; no suppression or suppression) X 2 (test; no suppression or suppression) X 2 (type; recollection or familiarity) X 2 (time; session one or session two) experimental design with study and test conditions as between groups variables and type and time as repeated within participants variables. Participants completed the first session of Jacoby s process dissociation task to obtain baseline scores. Participants were then randomly assigned to groups which differed on when they would be asked to engage in concurrent suppression. Control participants were asked to express and then suppress a telephone pole. The other three groups were asked to nominate a personal negative experience from their own lives. After practicing expressing and suppressing their target thought, all participants completed the second session of the memory task, with groups two through four continuing to suppress their target thought during either the study phase (condition 2), the test phase (condition 3), or during both study and test phases (condition 4). Participants in the control condition experienced an improvement on the explicit portion of the memory task, and a decline on the implicit portion of the memory task. Participants in conditions three and four experienced a decline in the explicit portion of the memory task, while their implicit scores remained unchanged. Findings are discussed in terms of Wegner's Ironic Processing model.

2 THOUGHT SUPPRESSION: DIVERGENT IMPLICATIONS FOR EXPLICIT AND IMPLICIT MEMORY by KEVIN MICHAEL BRATTON A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy PSYCHOLOGY Raleigh, North Carolina 2007 APPROVED BY: Dr. Douglas Gillan Dr. Denis Gray Dr. Kitty Klein Chair of Advisory Committee Dr. Chris Mayhorn

3 ii BIOGRAPHY Kevin Michael Bratton was born in Champagne-Urbana, Illinois on August 12, He graduated from Northmont Senior High School in 1987 and entered the University of Toledo in the fall of He graduated in the fall of 1999 with a Bachelor of Arts in Psychology. Realizing his enjoyment of research, he entered the graduate program in Social Psychology at North Carolina State University in the fall of He earned his Masters of Science in Psychology in the fall of Kevin subsequently continued his education in the field of social psychology by attending the doctoral program at North Carolina State University. Throughout his graduate career, he has been active in research and teaching in the undergraduate program at North Carolina State University as well as at Central Carolina Community College. Kevin s post-graduation plan is to work as a faculty member at a university in the United States while continuing his research.

4 iii ACKNOWLEDGMENTS This research has been a lengthy collaborative experience including many faculty, graduate, and undergraduate students. There have been a number of people who assisted in developing the design, collecting the data, and statistical analysis. This research is a product of these very talented individuals and I wish to express my gratitude. First, I would like to thank my advisor, Dr. Katherine Klein. Dr. Klein was essential for the completion of this study. She was intimately involved with every phase of this research, and made herself tremendously available to me for the numerous glitches that occur when conducting research. She gave me access to the laboratory and the tools I would need to complete this research. Moreover, her gentle prodding was very helpful in motivating me to complete this work. I would like to thank Dr. Lynne Baker-Ward for always making time for me. I spoke with her early in my graduate career about my research and she showed great interest. She continually encouraged me in my research. Dr. Denis Gray was a key component in this research. I counted on him to analyze my proposal and find any design errors that could contaminate the research. He was also occasionally sought for critical statistical information. I would also like to thank Elwyn Martin, Christina Costanzo-Mendat, Phillip Braddy, Sara Wren, and Kyle Huff for their contributions to conversations about the design and the interpretation of the results. Lastly, I would like to thank my wife, Susan, and my child, Andrew, who motivated me to complete my degree.

5 iv TABLE OF CONTENTS LIST OF TABLES vi LIST OF FIGURES..vii INTRODUCTION... 1 Cost of Suppression on Cognitive Tasks... 5 Individual Differences in Working Memory (WM); Influence on Cognitive Tasks...17 Individual Differences in Suppression Ability; Relationship with WM...24 METHOD...31 Participants...31 Materials...31 OSPAN...32 Process Dissociation Task...33 Thought Control Ability Questionnaire...35 Impact of Events Scale...36 Apparatus...36 Procedure...36 RESULTS...38 DISCUSSION...48 REFERENCES...60 APPENDICES...67 APPENDIX A: WORDS, STEMS, BASERATES, FREQUENCIES, AND SET SIZES...68 APPENDIX B: WORDS, STEMS, BASERATES, FREQUENCIES,

6 v AND SET SIZES...69 APPENDIX C: STUDY LISTS...70 APPENDIX D: STEM COMPLETION LIST ONE...71 APPENDIX E: STEM COMPLETION LIST TWO...72 APPENDIX F: STEM COMPLETION LIST THREE...73 APPENDIX G: STEM COMPLETION LIST FOUR...74 APPENDIX H: STEM COMPLETION LIST FIVE...75 APPENDIX I: STEM COMPLETION LIST SIX...76 APPENDIX J: STEM COMPLETION LIST SEVEN...77 APPENDIX K: STEM COMPLETION LIST EIGHT...78 APPENDIX L: THOUGHT CONTROL ABILITY QUESTIONNAIRE...79 APPENDIX M: IMPACT OF EVENTS SCALE...80 APPENDIX M: IMPACT OF EVENTS SCALE (cont.)...81 APPENDIX N: NEGATIVE EXPERIENCE NOMINATION REQUEST FORM...82

7 vi LIST OF TABLES 1. Mean Suppression Failures, OSPAN Scores, and Baseline Scores of the PD Task Repeated Measures ANOVA with Recollection and Familiarity Scores as a Function of Study and Test Conditions Intercorrelations Between OSPAN Scores and Baseline Estimates of the PD Task Intercorrelations Between OSPAN Scores and Suppression Failures Intercorrelations Between Suppression Failures in all Periods Intercorrelations Between the IES Sub-scales and Total IES

8 vii LIST OF FIGURES 1. Mean Recollection Scores by Study and Test Conditions across Time Mean Familiarity Scores by Study and Test Conditions across Time..43

9 1 Introduction Stressful experiences tax an individual s ability to adapt to their environment. McKinnon, Baum, and Morokoff, (1988) conclude that, stressful events include the threat of being harmed, strong environmental demands or loss of something valued (p. 43). Experiencing these stressors often leads to intrusive thoughts. Intrusive thoughts are thoughts that are brought into conscious awareness without being consciously requested. These intrusive thoughts are often unwanted for two reasons. First, they may interfere with the task the person is consciously engaged in at the time. This interference may cause deficits in sustaining controlled attention, or may impair one s ability to inhibit stimuli that are unrelated to the task at hand. Second, intrusive thoughts are associated with increased negative affect (Wenzlaff, 1991, cited in Wenzlaff & Wagner, 1998). Because intrusive thoughts about stressful experiences are unwanted, we try to avoid them (Manne, 1999). People use a variety of techniques to avoid intrusive thoughts. They may attempt to replace the unwanted thought, distract themselves, or rely on drugs or alcohol to alleviate the negative feelings associated with these intrusive thoughts. Due to the recurrent and unwanted nature of intrusive thoughts, people often engage in these strategies to regain mental control. The most common method used to remove unwanted intrusive thoughts is intentional thought suppression. Thought suppression is defined as the intentional and controlled removal of a thought from conscious awareness. Freud thought that some thoughts were so disturbing or unacceptable that we unconsciously eject them from conscious awareness. This unconscious, unplanned ejection of thoughts from conscious awareness is termed repression. I will deal exclusively with suppression

10 2 of unwanted intrusive thoughts, and it will become important to distinguish the characteristics of this particular strategy of dealing with intrusive thoughts. How suppression is accomplished may be more complex than it first appears. Wegner (1994) proposed an Ironic Process of Mental Control that described the structural components and processes involved with intentional thought suppression. Wegner s theory states that there are two processes that work together to suppress an unwanted thought: an operating system and an ironic monitor. The operating system is a controlled process, which endeavors to create the desired state of mind (Wegner 1994, p.37). The operating system is used to bring items into conscious awareness, such as a controlled distracter, that will temporarily replace the unwanted intrusive thought. The controlled characteristic of the operating system brings with it limitations. It takes mental resources to initiate the system and therefore, when resources run low, the operating system s effectiveness declines. Time pressure (Wegner & Erber 1992, Exp. 1) and imposition of a cognitive load (Wegner & Erber, 1992 Exp. 2; Wegner, Erber, & Zanakos, 1993, Exp. 1 and 2) have been shown to decrease an individual s ability to suppress or cause impairment on another controlled concurrent task. The other process is an ironic monitor. The ironic monitor is an automatic, uncontrolled process that constantly browses through the conscious contents of the mind looking for anything that is not associated with the desired state. If the monitor finds items that imply failed mental control, it increases their activation. This heightened activation increases the likelihood that these items will return to conscious thought. The uncontrolled characteristic of the ironic monitor suggests that it does not consume mental resources and therefore, should not be affected by diminished resources.

11 3 The irony of this theory involves the interplay between these two processes. The monitor will keep looking for anything not associated with the desired state. Because of the increased activation mentioned earlier, and the fact that this process does not use mental resources, the monitor will eventually find an item in consciousness that is associated with the thought to be suppressed. The monitor will then alert the operating system to run again to find a new suitable distracter. Once the operating system has found a new distracter, the monitor begins searching again. In the absence of a cognitive load, people are capable of suppressing unwanted intrusive thoughts by temporarily distracting themselves. Wegner s research suggests that while suppression may not be effective over long periods of time, it may be successful temporarily (Wegner 1994; Wegner, Schneider, Carter, & White, 1987). Suppression of unwanted intrusive thoughts may be successful and may lead to alleviation of the negative feelings associated with them. However, when suppression fails, the unwanted thought will return to conscious awareness along with the negative feelings associated with them. Wegner s ironic process model shares several key features with current models of working memory. Working memory is a limited capacity system allowing controlled sustained attention in the face of distractions or interference. This memory system is seen as that part of short-term memory that is actively rotating, computing, or otherwise mentally manipulating inner representations of the world. Controlled attention is required to selectively attend to only those pieces of information that are relevant to the task at hand, and to inhibit all other non-relevant information (Kane & Engle, 2000). Intrusive thoughts are examples of non-relevant information that need to be inhibited so as not to

12 4 infringe on the resources needed to complete the task at hand. Thought intrusions are believed to occur automatically. Interestingly, once the intrusive thought has entered consciousness, intentionally controlled thought suppression may temporarily remove it from conscious awareness at the expense of reducing the available resources for completing the task. Working memory includes both aspects of controlled attention and inhibition. Inhibition requires attentional resources as well (Hasher & Zacks, 1998). Considering the limited capacity of working memory, the amount of mental resources available for controlled, sustained attention is negatively related to the amount of mental resources available for inhibition. When the pool of mental resources runs low, there is likely to be a failure in either controlled attention or inhibition, with both resulting in the interruption of the task at hand. While some working memory theorists only consider the ability to sustain controlled attention (Conway & Engle, 1994), the consequences of diminished resources will be the same. Suppression of stressful intrusive thoughts may drain the resource pool and increase the probability of intrusions due to a lack of controlled attention, resulting in a failure of inhibition, or may cause impairments on other consciously controlled mental tasks. The purpose of this study is to investigate individual differences in suppression ability and working memory, and the effects suppression may have on other concurrent cognitive tasks. Wegner s directed suppression methodology is the most common way of empirically investigating thought suppression (Wegner, Schneider, Carter, & White, 1987). After practicing how to report their stream of consciousness, participants are instructed to either express or suppress a white bear for the first five-minute period. Next,

13 5 instructions are reversed for both groups. They are also instructed to ring a bell on the table whenever a white bear comes to mind in both the express and suppress conditions. The results indicate that the numbers of thoughts about a white bear are more prevalent in the expression condition, although thoughts of the white bear are more frequent in the expression period following initial suppression than in the initial expression period. A similar effect is not found in the suppression period following initial expression. The authors conclude that initial suppression appears to produce a rebound effect. A negative cue hypothesis has been developed to explain this phenomenon. The negative cue hypothesis suggests that thinking without focus is difficult and proposes that participants attempt to distract themselves by using cues in the environment. However, in the following expression period, these negative cues constantly remind one of what was previously forbidden to think about. While the rebound effect helps us to understand the persistence of unwanted intrusive thoughts, the consequences of suppression on other cognitive tasks need to be further examined. I will begin by examining the empirical research related to the differential cost of suppression on other non-related tasks. Next, I will review the literature concerning individual differences in working memory and the influence working memory has on different cognitive tasks. Finally, I will discuss the research on individual differences in people s ability to suppress unwanted thoughts and how this difference is related to working memory. Cost of Suppression on Cognitive Tasks Wegner, Erber and Zanakos (1993) used the Stroop color-naming task with and without a cognitive load to measure the ironic effects of suppression. Participants were

14 6 asked to suppress or think about a recent personal success or failure. The Stroop words were either related or unrelated to the personal experiences. Under low cognitive load, participants speed at naming the color of the words on the task was unaffected by suppression. Under high cognitive load, participants who had been asked to suppress their personal experiences were slower to name the color of the experience-related words compared to participants asked to think about their personal experiences. These results suggest that suppression of a success or failure under cognitive load makes that success or failure more accessible than other irrelevant thoughts, and resulted in slower task performance. Hodges and Wegner (1997) investigated the effects of suppression on an explicit memory task. The authors completed a study in which participants were asked to assume or reject the perspective of another person. Participants read a story in which two boys played in a house that is described in detail. The experimental conditions included a control group who simply read the story, a title group (who were given the story to read with the title, Would you rob this house? ), a think like a burglar group and a not think like a burglar group. All participants were assigned to either a low or high cognitive load (remember a one-digit or six-digit number while reading the story). Under low cognitive load, the think like a burglar group recalled more burglar relevant information compared to the control and the not think like a burglar groups. The not think like a burglar group under high cognitive load recalled more burglar relevant information than the not think like a burglar group under low cognitive load. Moreover, under high cognitive load, the not think like a burglar group recalled more burglar relevant information than the think like a burglar group or the control group. These results suggest that suppression

15 7 conducted under cognitive load may cause the suppressed information to become hyperaccesible mirroring the results of Wegner and Erber, (1992). Macrae, Bodenhausen, Milne and Wheeler (1996) investigated the relationship between stereotype suppression and a probe reaction task. The authors asked participants not to suppress descriptions of a skinhead, suppress a less stereotypic description of a skinhead, or suppress a highly stereotypic description of a skinhead. The group who was suppressing a highly stereotypic description of a skinhead had slower response times on a concurrent probe reaction task compared to the other two groups. Unfortunately, suppression failures of the skinhead were not measured and the slower response times could be due to the distraction of the intrusions or to the cognitive cost of suppressing stereotypes. Nevertheless, participants attempting to suppress a highly stereotypical description of a skinhead experienced either unwanted intrusive thoughts or impairment on another controlled cognitive task. Wegner, Quillian and Houston (1996) predicted that one of the effects of intentional suppression is the disruption of episodic memory for extended event sequences. First, participants were shown a film clip of a coal miners strike that had a clear beginning, middle and end. Participants were then assigned to a control condition with no instructions, a suppression condition with the instructions, Do not think about the film clip today, or an expression group with the instructions, Think about the film clip all day. Five hours later, participants were asked to complete a number of memory measures. There were no group differences in overall memory or reports of the vividness of the memory of the film. Interestingly, participants who were asked to suppress thoughts about the film during the five-hour delay were less accurate in recalling the

16 8 sequence of events depicted in the film compared to participants told to think about the film all day or to the control group who received no instructions. These results suggest that thought suppression may also interfere with the temporal order of memories. Richards and Gross (2000) investigated the cost of suppressing emotional reactions to a film (Exp. 1) and to a slide show (Exp. 2). In experiment one, participants were assigned to a watch condition (where they were asked to watch and listen to the film clip carefully) or an expressive suppression condition (where they were asked to hide their emotional reactions to the film clip). They were then asked to watch a film clip that depicted an argument between a husband and wife about an extramarital affair in front of their children. Participants in the expressive suppression condition showed poorer memory for the visual and auditory details compared with participants asked to merely watch the film clip. Moreover, participants asked to suppress their emotional reactions to the film clip reported less confidence in their memory compared to those asked to watch the film clip. Apparently suppressing emotional reactions produces a cognitive impairment in memory and a reduction in confidence for that memory. To address a few methodological concerns from the previous study, Richards and Gross (2000) included a reappraisal condition and a second level of emotional intensity in experiment two. Participants were assigned to a watch condition, an expressive suppression condition or a reappraisal condition (where they were asked to try their best to adopt a neutral attitude toward the slides). The slides contained verbal information (name, occupation, and injury) and non-verbal information (the actual image of the injury). The injury images were of a high emotional intensity (people who appeared gravely injured) or low emotional intensity (people who appeared healthy because they

17 9 had healed). Participants in the expressive suppression condition showed poorer memory for verbally encoded information presented during the high emotion slides compared to participants in the watch condition. Interestingly, the reappraisal condition enhanced nonverbal memory. These results also suggest that suppression of emotions may drain resources available for ongoing processing. In a study by Klein and Bratton (in press) participants were randomly assigned to a neutral personal experience, a non-personally relevant negative experience, a personally relevant negative experience thought condition, or a non-suppression control condition. The control group simply completed the dependent measures which included a sentence verification task; a modified version of the Speed and Capacity of Language Processing Test (Baddeley, Emslie, & Nimmo-Smith, 1992). After practicing the sentence verification task and intentional suppression, the remaining participants were asked to spend three minutes expressing their target experience followed by three minutes suppressing their target experience. Next, the participants were asked to suppress their target experience while concurrently completing the sentence verification task. Initial analysis revealed that those who had the hardest time practicing suppression also had more failures while suppressing their personal experience. Results from the dual task period revealed that participants suppressing a personal negative experience had slower response times on the sentences compared to the control group and the group suppressing a non-emotional experience, but did not differ from participants suppressing a nonpersonal negative experience. Furthermore, these differences were exacerbated on the more complex sentences. Overall, these results lend support to the hypotheses that

18 10 suppression may have a cognitive cost on other controlled mental tasks, and that these costs increase as task difficulty increases. Harvey and Bryant (1999) investigated the role of anxiety in attempted thought suppression. The authors categorized participants as high or low in anxiousness. Participants were then assigned to a neutral or distressing film condition. After watching the film clip, participants were assigned to a think about anything group or a suppress thoughts about the film group. Next, the participants were asked to monitor their thoughts for any film-related thought while completing a lexical decision task. There were no differences between suppressors or non-suppressors in the number of film related intrusions for those in the high anxiousness group during the concurrent task period. However, those given suppression instructions in the low anxiousness group during the concurrent task period experienced significantly more film-related intrusions compared to those given no such instructions. The authors concluded that participants who were categorized as highly anxious engaged in defensive suppression, which reduced the paradoxical effects seen in other studies. While there were no significant group differences in the lexical decision task, the cost of suppression in this study apparently resulted in the increased number of film-related thoughts during the concurrent task. While there are some questions about the nature of suppression effects and which cognitive tasks may be affected by this intentional process, thought suppression appears to have a negative effect on other controlled concurrent mental tasks. The key hypothesis of the proposed study is that thought suppression will cause impairment on the explicit portion of a process dissociation task as both are controlled, effortful processes but should have little to no effect on the implicit portion of the process dissociation task.

19 11 Most previous research examining the cognitive costs of thought suppression has used explicit memory tasks. Performance on explicit memory tasks refers to those mental processes involved in controlled cognition. Controlled cognition implies that the information is available to conscious awareness, and can be purposely retrieved from memory if there are adequate resources available. In contrast, performance on implicit memory tasks refers to those mental processes involved in uncontrolled cognition. This uncontrolled (automatic) cognition implies that the information is not available to conscious awareness and therefore, is not subject to conscious retrieval. Because uncontrolled cognition does not draw from the resource pool, performance on the implicit task should not be affected by suppression attempts. Current theories of working memory and competition for resources suggest that suppression uses cognitive resources and that this diminished resource pool has effects on other consciously controlled mental processes, but should leave the more automatic processes unhampered. To the extent that these premises are true, directed suppression should have effects on the performance of explicit memory tasks, but performance on implicit tasks should remain intact. I will now cover previous research that has investigated separating the influences of controlled versus automatic processing and research that has employed memory tasks that include both explicit and implicit components. Jacoby, Woloshyn & Kelley (1989) sought to separate the independent influences of conscious recollection versus familiarity in memory tasks. The participants were first asked to read a list of non-famous names with full or divided attention. Next, the participants were asked whether names shown to them were famous or non-famous. They were told that all of the names from the previous list were not famous. If the participants

20 12 recognized a name from the first list it must be non-famous. Those who studied the list under full attention were later less likely to call an old non-famous name famous than new non-famous names. This was due to the fact that the participants presumably remembered some of the old names from the first list. On the other hand, those who studied the list under divided attention, were more likely to call an old non-famous name famous than new non-famous names. The divided attention condition interfered with the level of processing which lowered the probability of remembering the old names from the first list. The divided attention condition caused the participants to call old names famous due to familiarity and not recollection. However, placing recollection and familiarity in opposition to each other may cause one to underestimate the process of familiarity. Results suggest that it is possible to separate the independent contributions of recollection and familiarity in memory tasks. To investigate the possibility that placing recollection and familiarity in opposition to each other causes an underestimation of familiarity, Jacoby, Toth, and Yonelinas (1993) discussed a general approach to separating the influences of controlled and automatic cognition on laboratory tasks. The process-dissociation procedure defines conscious control as the difference in performance between conditions where one is trying to do something versus trying not to do something (Kelley and Jacoby, 1998 p.131). The authors suggest using both an exclusion condition to estimate familiarity and an inclusion condition to estimate recollection. The inclusion score is the probability of recollection (R) plus the probability of the word automatically coming to mind (A) when there is a failure of recollection (1-R): Inclusion = R + A (1-R). (p. 141)

21 13 The exclusion score involves the probability that the word automatically comes to mind (A) and a failure to recollect that it was seen earlier (1-R): Exclusion = A (1-R). The probability of recollection is equal to the inclusion score minus the exclusion score: R = I-E. The probability of familiarity is equal to the exclusion score divided by the equation for when there is a failure to recollect: A = Exclusion/ (1-R). The previous equation estimate reflects both the automatic influences of memory (M) and the baseline probability of responding with a particular word: A = M + B. Given that these premises are true, one can calculate the independent influences of automatic memory by subtracting the baseline probability of responding with a particular word from the estimate of A: M = A B. Original attempts to estimate recollection and familiarity used two separate tests. This relied on the assumption that the two processes were relatively pure. In contrast, the process dissociation procedure allows one to estimate both the independent influences of recollection and familiarity within a single task. If these two processes have independent effects on a task, researchers should be able to create manipulations that either only affect one of these processes, or even better, have opposite effects on these processes. For obvious reasons, there is a definite advantage to using the process dissociation procedure

22 14 to estimate the independent contributions of recollection and familiarity in laboratory memory tasks. Jacoby (1998) discussed the general approach to separating the influences of controlled and automatic cognition on laboratory tasks in recent studies. In three experiments the authors manipulated instructions (Direct-retrieval versus generaterecognize), attention during study (full versus divided), presentation duration during study (one versus ten seconds) and presentation of items (separate versus intermixed). In experiment one, the authors manipulated instructions and investigated the effects of full versus divided attention during study. Half of the participants were assigned to the directretrieval condition (DR) and half were assigned to the generate-recognize condition (GR). Direct-retrieval instructions required participants to avoid words specifically on the basis of recollection. Exclusions in the generate-recognize instructions would result from an old word automatically coming to mind, without being recollected which would then be checked for recognition and would be avoided because it was recognized. Half of the participants from each group were assigned to the full attention study condition and half of the participants were assigned to the divided attention study condition. Participants were asked to read 40 study words aloud that were presented on a computer screen one at a time and to remember them for a future memory test. The divided attention groups were asked to listen to a recorded list of digits and to detect any sequences of three odd digits in a row while reading the study words aloud. In the final phase of the study, participants were presented with word stems, consisting of the first three letters of a five-letter word on a computer screen one at a time. For participants in the DR condition, each word stem was presented with a prompt (NEW or OLD) and the inclusion and exclusion tests were

23 15 intermixed. Participants were instructed that if the prompt was OLD, their job was to use a recalled word as a completion. If the prompt was NEW, their job was to not use a recalled word as a completion, and they were further instructed to use a different word to complete the stem. For participants in the GR condition, word stems were presented without prompts, and the inclusion and exclusion tests were blocked. Participants in this condition were asked to check each completion word that came to mind and make sure it was not presented earlier for the exclusion condition. For the inclusion condition, participants were asked to complete the word stem with the first five-letter word that came to mind that fit the stem. Inclusion test scores were higher for the DR condition compared to the GR condition, and were higher under full attention compared to divided attention during study. Exclusion test scores were higher for the GR condition compared to the DR condition, and were higher under full attention compared to divided attention during study. Of specific interest, analysis of A revealed a process dissociation. Results from the DR instructions revealed that dividing attention during study produced a decrease in R, but left A unhampered. An opposite dissociation was found from the GR instructions. Results revealed a decrease in R, but an increase in A. For words studied under full attention, A was significantly below baseline (p.8), which is a sign that the assumptions of independence and equality of R had been violated. The authors concluded that direct-retrieval instructions were the appropriate choice when conducting research on process dissociations. In his second study, Jacoby manipulated presentation duration during study (one versus ten seconds) as a within subjects variable. Half of the participants received the short duration study list first and half of the participants received the long duration study

24 16 list first. After the first study list was presented the participants were reminded to read the words aloud and try to remember them for a future memory test. Jacoby also included the remember-know procedure during the stem completion phase. As word stems were presented to the participant, they were instructed to use the stem as a cue to recall a word from the study list. If the participant could not recall a word from the study list, they were to complete the stem with the first five-letter word that came to mind and fit the stem. Once a stem was completed, the participant evaluated their response as remember, know or new. The participant would respond with remember if they could consciously remember details of the word from one of the study lists. A know response was to be given if the participant knew that the word had been presented in one of the study lists but could not remember any details of the word from the study list. If the participant believed that the word had not been presented on either of the study lists they were asked to respond, New. Combining know and new responses (direct-retrieval), reducing study time decreased R, but left A invariant. Combining know and remember responses (generate-recognize), reducing study time decreased R, and increased A. Jacoby concluded that the difference in outcomes due to the different procedures used to estimate R and A explains the disagreement in the current research literature; combining know and remember responses instead of know and new response violates the assumption of the process dissociation procedure. Taken together, these results suggests that researchers should consider carefully the instructions they give to participants and the procedures they use to estimate R and A. Jacoby concluded that, To meet the assumptions underlying the process-dissociation

25 17 procedure, it is important that instructions encourage participants to exclude items only because they recollect (remember) earlier studying the items (p.17). Individual Differences in Working Memory (WM); Influence on Cognitive Tasks The next issue involves investigating individual differences in working memory. There are individual differences in people s capacity to control attention (Engle, Kane & Tuholski, 1999) and this difference manifests itself on laboratory tasks. Fink and Neubauer (2004) examined the relationship between working memory and subjective time estimations and found that individuals with higher WMC made more accurate time estimations on a task than those with lower WMC. It is not known if people with higher working memory will experience lower dual task costs arising from efforts to suppress a personal memory. Oberauer, Lange, and Engle (2004) examined the relationship between WMC and the ability to resist interference. Participants working memory capacity was assessed with four standard measures in a previous study. Participants were asked to complete a number of verbal and spatial tasks, which included either a single or dual task component. In the dual tasks, the researchers varied the phonological and semantic similarity to investigate their relationship with WMC. Dual task costs (DTC) were modestly correlated with WMC, although the authors concluded that, the correlations between DTC and WMC are artifacts from non-linear transformations on the differences between single- and dual-task performances (p.91). The authors suggest that dual task interference had an additive effect (or better: subtractive) effect on performance, whether measured as span or percentage correct, independent of a person s working memory capacity (p. 92). Semantic and phonological similarity had little, if any effect

26 18 on dual task costs. More importantly, there were no significant correlations between dual tasks costs across the domains. The researchers suggest that these results lend no support for the idea of a domain-general central executive. However, the researchers used content from the same domain for the secondary task. The authors propose that the difference between simple and complex span tasks cannot be explained by the added component of a central executive or general executive attention. Results suggest that there is a relationship between WMC and the ability to resist interference. Rosen and Engle, (1998) investigated individual differences in working memory capacity and how they are related to people s ability to inhibit information in two experiments. In experiment one, participants were prescreened with a modified version of Operation Span Task (OSPAN; Turner & Engle, 1989). Next, the participants were assigned to an interference condition or a non-interference condition for the paired associate task. The paired associate task involved participants learning three lists of twelve word pairs. Participants were instructed that speed was crucial and that their goal was to say the correct response before the deadline. High span participants needed fewer trials to reach the criterion level, produced fewer total intrusions, and produced fewer intrusions per trial on the second-list compared to low spans. Results from experiment one imply that there is a negative relationship between WMC and vulnerability to intrusions. In Rosen and Engle s (1998) second experiment they investigated the relationship between individuals WMC and their ability to suppress intrusions. The procedure was the same as in experiment one except that instead of speed, participants were instructed that accuracy was crucial and that their goal was to really try hard to come up with the

27 19 correct response. High span participants in the interference condition took longer to retrieve response items from the first-list on the first trial of the third-list compared to their control. Low span participants were faster than their control. Moreover, high span participants in the interference condition took longer to retrieve response items from the first-list on the first trial of the third-list compared to when they first retrieved the same response items on trial one of the first-list. Low span participants in the interference condition showed little difference in response times between the first and third-lists. The authors concluded that, high span participants in the interference condition had suppressed first-list response items during second-list learning, whereas the low span participants had not (p.430). Taken together, Rosen & Engle s (1998) two experiments provide strong support for the notion that WMC has a negative relationship with vulnerability to intrusions and a positive relationship with the ability to inhibit intrusions. Beilock and Carr (2005) investigated individual differences in working memory and the effects of psychological pressure on a mathematical problem-solving task. The participants first completed two working memory measures: Turner and Engle s (1989) Operation Span and Daneman and Carpenter s (1980) Reading Span. The participants were then asked to complete Gauss (1801) modular arithmetic task (cited in Bogomolny, 1996). The task involved solving a number of mathematical equation and deciding if the answers were whole numbers or not. There were an equal number of high and low difficulty equations. In the low pressure condition, there were no significant differences between the high and low working memory capacity groups. Under the high pressure condition, those in the high working memory capacity group showed significantly diminished scores on the high difficulty equations, whereas the low working memory

28 20 group s scores slightly improved on the high difficulty equations. The authors suggest that those with higher working memory may be disadvantaged when high difficulty levels and high pressure demands are concurrent, but that lower working memory individuals may not suffer the same diminishment in performance due to their scores already being near floor effects. These findings suggest that when high span participants working memory resources are depleted due to psychological pressure that performance on a controlled task with a high cognitive load may suffer. Unsworth and Engle (2005) conducted a study to examine individual differences in working memory and their relationship to both incidental and intentional learning. The participants were pre-screened with the OSPAN for working memory capacity. Participants were then asked to practice a serial reaction time task involving locating an asterisk on the computer screen in one of four locations. Next, participants completed twelve blocks of trials with five blocks consisting of random sequences of asterisks locations and seven blocks consisting of repeating sequences of asterisks locations intermixed. Results of the practice trials showed that those in the high working memory condition were faster than those in the low working memory condition. During the repeating sequences, the high span group was faster, but both of the groups performances increased at the same rate. During the random sequences, the high span group performed significantly faster than the low span group. Results suggest that high and low spans do not differ in performing the unintentional task, but do on the intentional explicit task. Results suggest that individual differences in working memory manifest themselves on tasks that require controlled processing, but have little or no implications for automatic processing.

29 21 Pulos and Denzine (2005) investigated individual differences in working memory and planning behavior using a computerized version of the Tower of London task (Welsh, Satterlee-Cartmell, & Stine, 1999). The participants completed a visuo-spatial span task, a verbal-span task, a trail making task, a standardized version of the Stroop task (Trenerry, Crosson, DeBoe, & Leber, 1989), and the Tower of London (TOL) task. The average solution time of the TOL was significantly correlated with both the visuospatial-span task and the verbal-span task (.41 and.26 respectively). The number of excess moves was not significantly related to any of the working memory tasks. The authors suggest that individuals with higher working memory scores develop more efficient online planning strategies by making larger partial plans and therefore do not need as many iterations of the partial plan-execution cycle. Those with lower working memory tend to make smaller partial plans and thus must engage in more cycles to attain the desired outcome. The authors also point out that the correlation between the visual and verbal WMC tasks was only.07 suggesting that these make independent contributions to the TOL task. Apparently, individuals working memory capacity is also significantly related to planning behavior. Bleckley, Durso, Crutchfield, Engle and Khanna (2003) investigated individual differences in working memory capacity and the ability to allocate visual attention. The authors used the operation-word-span task (OSPAN) to measure working memory capacity (WMC). Using a modified visual attention allocation task, participants were asked to identify a letter flashed briefly in the middle of a three concentric octagonal pattern and to locate a letter presented outside of the fixation point. Trials were uncued, validly cued or invalidly cued for the letter outside of the fixation point (close, medium or

30 22 distant). On the invalidly cued trials, individuals with high span compared to low span condition showed poorer location of the displaced letter when it was presented on a ring closer to the fixation point than the one cued. The authors concluded that the low span WMC participants used their attention much like Posner et al. s (1980) spotlight metaphor, and that high span WMC participants were able to inhibit the non-cued rings. Low span WMC participants were less able to ignore the non-cued rings, which allowed the participants to correctly locate the letter when it was presented on a ring closer to the fixation point. However, the design of this study did not allow the researchers to specify whether the high span WMC participants inhibited information on the uncued rings, focused their attention on the cued rings or some combination of both explanations. Nevertheless, results are consistent with previous research that suggests WMC is related to controlled attention and inhibition of non-goal relevant information. Unsworth, Schrock, and Engle (2004) investigated the relationship between working memory capacity and inhibition ability with a prosaccade and antisaccade task. The authors pre-screened participants using the OSPAN. In the prosaccade task, participants were asked to make their first eye movement in the direction of the flashing square. In the antisaccade task, participants were asked to make their first eye movement in the opposite direction of the flashing square. On the prosaccade task, working memory span was not related to speed or accuracy during the task. Moreover, both groups were faster on the prosaccade versus the antisaccade tasks. On the antisaccade tasks, participants in the high span condition were faster and more accurate compared to participants in the low span condition. Apparently, participants with low spans

31 23 experienced more difficulty inhibiting the natural response to move their eyes in the direction of the flashing square. In their second experiment, the researchers presented the participants with trials of prosaccade and antisaccade tasks intermixed to increase the demands on attention on both the antisaccade and prosaccade tasks. The procedure was similar to experiment one except that the white plus sign was replaced with either a white circle or a white diamond to indicate if the trial was prosaccade or antisaccade, and after 80 trials the symbol meaning was switched. Results replicated those in study one as prosaccade trials were completed faster and more accurately than antisaccade trials for both groups. More importantly, low span participants made more errors on both prosaccade and antisaccade tasks compared to the high spans. There was only a marginal difference in speed between the high and low spans. These two studies suggest that low span individuals are poorer at controlling attention to directions and inhibiting natural response to stimuli that are nongoal relevant compared to high span individuals. Conway, Cowan, and Bunting (2001) examined the relationship between participants working memory spans and their ability to inhibit irrelevant, non-goal directed information using a dichotic listening task. The participants were given headsets and were then asked to listen to the message in their right ear and ignore the message in their left ear, and to shadow each word out loud that was presented in their right ear. Participants were randomly assigned to a condition where the authors inserted their first name in their left ear after either four or five minutes of shadowing. Immediate retrospective reports showed that only 20% of the high span participants heard their first name in the irrelevant message compared to 65% of the low span participants. The

32 24 authors propose that the low span individuals were less able to block information from the irrelevant message compared to high spans. Interestingly, shadowing errors before presentation of their names were equal between the groups, but errors were significantly higher after the presentation of their names for both groups relative to those who had not heard their names. The authors concluded that previous research supports the interpretation that high span individuals are better at inhibiting distracting information. Individual Differences in Suppression Ability; Relationship with WM I have presented evidence that thought suppression can impair performance on concurrent cognitive tasks, that a dissociation paradigm can be used to separate deliberate and automatic influences in memory, and that differences in working memory capacity are related to individuals performance on laboratory tasks, their ability to attend to laboratory tasks and their ability to inhibit irrelevant information while completing a task. There is also evidence that differences in individual s working memory capacity are linked to the ability to suppress unwanted thoughts. It is reasonable to believe that some people have either a larger resource pool (Just & Carpenter, 1992) or they use the resource pool more efficiently, and this should be related to an individual s ability to suppress unwanted thoughts. Brewin and Beaton (2002) investigated the relationship between working memory, intelligence, and suppression ability. The authors measured fluid intelligence using Raven s Standard Progressive Matrices (Raven, Court, & Raven, 1977), crystallized intelligence using the National Adult Reading Test (NART-2; Nelson & Willison, 1991), and assessed working memory capacity using OSPAN. During a first five-minute period participants were asked to report their stream of consciousness