Frontal Lobe Functioning in Adolescents with Attention Deficit Hyperactivity Disorder

Article excerpt

Attention deficit disorders affect three to five percent of school-aged children (DSM-IV, American Psychiatric Association, 1994). The diagnosis of attention deficit hyperactivity disorder (ADHD) is relatively unambiguous. Typically, ADHD diagnosis is based on behavioral observations in which the individual must display a number of developmentally inappropriate symptoms of inattention and hyperactivity-impulsivity. These symptoms must be observed in early childhood, be present in two or more settings, and remain consistent for a minimum of six months.

Less clear is the etiology of ADHD. Originally conceived as a child disorder, it is now recognized that ADHD continues into adolescence and adulthood, suggesting a more permanent basis for the disorder (Brown & Borden, 1986; Lambert, Hartsough, Sassone, & Sandoval, 1987). In an effort to understand the source, investigators have attempted to identify common characteristics of children, adolescents, and adults with ADHD using both cross-sectional and longitudinal studies. In a review of longitudinal studies by Klein and Mannuzza (1991), it was suggested that previously diagnosed children had higher rates of antisocial personality disorder and substance use disorders. Barkley, Fischer, Edelbrock, and Smallish (1990) examined a sample of previously diagnosed children. After eight years, they found that the majority still met criteria for ADHD, with 59% of these also meeting criteria for oppositional defiant disorder (ODD) and/or conduct disorder (CD). It was also reported that the proband group had a higher rat e of academic problems, including suspension, drop out, expulsion, and having failed a grade.

Another common finding in many follow-up studies is the report that individuals with a childhood diagnosis of ADHD are more likely to have an antisocial personality disorder or a nonalcohol substance use disorder as compared to a control group (Biederman, 1998; Mannuzza, Klein, Bessler, Malloy, & LaPadula, 1993; Mannuzza, Klein, Bessler, & Malloy, 1998). These studies also report that the proband group completed less schooling and had significantly lower occupational rankings. Milberger et al. (1997) also found that ADHD probands had a high risk for future substance abuse. Follow-up studies have shown that individuals diagnosed with ADHD in childhood have problems during adolescence and adulthood.

Given the early onset and consistency of symptoms associated with ADHD, present research has focused on central nervous system (CNS) substrates of ADHD. The area of study that appears to be promising is the frontal lobes of the brain. Mattes (1980) was the first to relate frontal lobe dysfunction with attention deficit disorder (ADD). Mattes linked ADD symptoms with symptoms arising from frontal lobe lesions in animals and humans. He further suggested that individuals with ADD and those with frontal lobe damage exhibit similar deficiencies.

Since Mattes' study investigators have continued to examine a link between frontal lobe dysfunction and ADHD. The working hypothesis is that frontal lobe functioning is poorer in those with ADHD as compared to non-ADHD individuals. However, using standard neuropsy-chological test probes, the results have been inconsistent. For example, the Wisconsin Card Sorting Test (WCST) is commonly used to assess frontal lobe functioning. Using the WOST, a number of studies have found significant differences between ADHD and non-ADHD persons (Chelune, Ferguson, Koon, & Dickey, 1986; Gorenstein, Mammatto, & Sandy, 1989; Shue & Douglas, 1992). Other studies have found no differences on the WCST between ADHD groups and control groups (Carter et al., 1995; Grodzinsky & Diamond, 1992; Loge, Staton, & Beatty, 1990; McGee, Williams, Moffit, & Anderson, 1989). The contradictory results of the different studies may be due to the criteria used to define the groups, the measures that were used to assess frontal lobe functioning, co morbidity of the ADHD group, and the age of the participants.

For example, Barkley, Grodzinsky, and DuPaul (1992) compared four groups of children, an attention deficit hyperactive disorder group (ADD+H), an attention deficit disorder group (ADD-H), a learning disabled group (LD), and a normal control group. The ADD-H group consisted of 11 boys and the remaining groups all consisted of 12 boys. They ranged in age between 6-11 years old. An estimated IQ of 80 or above was required. The children had no evidence of deafness, blindness, severe language delay, cerebral palsy, epilepsy, autism, or psychosis. The ADD +H group had to meet DSM-III-R criteria for ADD+H, have a score on the Inattention and Overactivity scales of the Child Attention Profile greater than the 93rd percentile, and be removed from any stimulant medication for 48 hours before participation in the study. The ADD-H group had to meet the same criteria as the ADD+H group except for the scores on the Child Attention Profile. This group had to be above the 93rd percentile on the Inattention scale but below t he 84th percentile on the Overactivity scale. The LD group had to be currently placed in a program for LD children in their school, have no teacher complaints of inattention, overactivity, or impulsivity, and a score below the 84th percentile on the Inattention and Overactivity scales of the Child Attention Profile. Lastly, the normal control group had to have no history of mental health services, no parent or teacher complaints of significant behavior problems, scores on the Child Attention Profile below the 84th percentile, and no history of academic problems as reported by their mothers. All children were administered a number of tests assessing frontal lobe functioning. It was found that the attention deficit disorder (ADD) groups performed worse than the control group on the Continuous Performance Test, Stroop Color and Word Test (SCWT) color score, SCWT interference score, and the Controlled Word Association Test letters score. No differences were observed between the ADD groups and control group on the WCST, ReyOsterrieth Complex Figure, Porteus Mazes, and Trail-Making Test.

Shue and Douglas (1992) did find differences between ADHD and non-ADHD persons, aged 8-12 years. The criteria for ADHD included: referral to a hyperactivity project at a children's hospital, had to meet DSM-III criteria for ADHD, had to receive ratings of 1.5 or greater on the hyperactivity index of the Revised Conners Teacher Rating Scale and Parent Rating Scale, have no additional psychiatric diagnosis, symptoms not attributable to another medical cause, score above 80 on the Peabody Picture Vocabulary Test, and receive no medication 20 hours prior to the testing. The study gave no mention of possible learning disabilities being present in the ADHD or control group samples. The control group was matched on gender, age, and IQ. The control group was free of psychiatric disorders, and scored below 1.5 on the parent and teacher versions of the hyperactivity index. Results showed that the ADHD group performed significantly worse on the following tasks related to frontal lobe functioning: Go-No Go task, Conflic ting Motor Response Test, Trail-Making, and WOST.

These studies illustrate the inconsistent findings in the literature to date. The majority of studies examining frontal lobe functioning have focused on children with ADHD but have not studied adolescent populations at any length. Only a few studies have examined frontal lobe functioning in adolescents with ADHD. One study was a follow-up of children who had been diagnosed between 4-12 years old (Fischer, Barkley, Edelbrock, & Smallish, 1990). At the time of follow-up, the subjects were 12-20 years old. The subjects were categorized into two groups by age, one from 12-14 years old (n = 39), and the second ranged from 15-20 years of age (n = 21). It was found that the ADHD groups generally performed poorer on tasks of attention and impulse control. However, the study failed to determine precisely how many of the ADHD participants still had symptoms and would still meet diagnostic criteria. Therefore, it is entirely possible that the ADHD groups included those who no longer met the diagnostic criteria for ADHD . No differences between the ADHD and control groups on the tasks measuring frontal lobe functioning were found, but it was found that the younger group performed worse than the older group on these tasks.

A second study examining frontal lobe functioning in adolescents with ADHD by Seidman et al. (1995) was longitudinal. It consisted of males between the ages of 9 and 20 years. The ADHD group met diagnostic criteria and both groups met additional screening criteria. It was found that the ADHD group performed poorer on tasks of frontal lobe functioning. Almost half of the ADHD group was comorbid. It was also reported that 18 of the 65 participants in the ADHD group also had a learning disability. The study did not report results for the ADHD group without learning disabilities for the tests. Therefore, it was unknown if the presence of learning disabilities influenced the results.

More recently, a controlled study addressed the role of frontal lobe functioning in adolescents with ADHD. Seidman, Biederman, Faraone, Weber, and Ouellette (1997) conducted a study examining frontal lobe functioning in adolescents with ADHD employing the WCST, Stroop test, and Rey-Osterrieth Complex Figure. This study included a comparison of younger (< 15 years) and older ([greater than or equal to] 15 years) adolescents, with ADHD compared with controls. Also included were adolescents with ADHD who had comorbid disorders. No differences were found on the dependent measures between the ADHD only and the comorbid groups. This study serves as pilot work in the area of adolescents with ADHD and frontal lobe functioning. Data from this initial study have provided support for the hypothesis that frontal lobe functioning is compromised in ADHD.

The current study provides an exploration of frontal lobe functioning in a sample of ADHD adolescents. This study contributes to past studies by attempting to clarify the inconsistencies in past research focusing on children. It also contributes to the emerging research focusing on adolescent samples.

METHOD

Participants

A total of 20 adolescents were studied. Nine male and one female ADHD participants were recruited from the national support organization, Children and Adults with Attention Deficit Disorders, from a private pediatrician's office, and from public schools. Nine male and one female controls were recruited from friends of the ADHD participants. The sample size is commensurate with related studies reported in the literature. Within the parameters of [beta] = .80 and = .05, this sample size provides adequate power given the large effect and low variance associated with studies using matched groups, clinical versus nondlinical participants. The participants ranged in age from 12-17 years (mean ADHD 15.3 years; mean control = 15.2 years), assuring relatively mature psychomotor and cognitive development.

All participants were screened for ADHD to confirm previous selfreports and diagnoses. If an ADHD participant was on medication for the disorder, testing was done during a medication holiday. A total of six adolescents typically were treated with medication but at the time of testing were on medication holidays and had not taken any medication for days, or in three cases weeks, prior to testing. No control participants were under treatment and/or medication during the study.

Screening data are displayed in Table 1. The Conners Parent Rating Scale-Revised (CPRS-R) showed all ADHD participants to have clinically elevated T scores (> 60) on the ADHD Index and Hyperactivity Index. A similar pattern was obtained for ADHD participants on the Adolescent Self-Report Scale as well. Controls' scores were unremarkable. The CPRS-R also was utilized to screen for conduct disorder and oppositional defiant disorder, and all participants had a T score under 60 on the conduct problems index.

Neurocognitive status was determined through interview and standardized psychometric instruments. All participants were screened for a history of head injury and epilepsy as assessed by a brief interview with a parent. Additionally, all participants scored within one standard deviation of the mean on the Peabody Picture Vocabulary Test-III (PPVT-III). This test was used to ensure that all participants were of average intelligence. The Wide Range Achievement Test-Revised (WRAT-R) was utilized to screen for possible learning disabilities. Given the prevalence of comorbidity with ADHD, it was important to include a screening measure for learning disabilities. All participants scored within one standard deviation on each of the three scales. Control participants also were screened for ADKD. All had a T score below 60 on the Hyperactivity Index and ADED Index of the CPRS-R. All control participants were also screened for medication use and history of psychiatric illness.

Screening Measures

Conners Parent Rating Scale-Revised (CPRS-R). This is a 48-item, Likert-scale, self-report measure completed by parents regarding their perceptions of their adolescent's behaviors (Conners, 1997). The CPRSR is a common measure used in research with attention deficit disorders. The use of this measure has been recommended as part of a standardized assessment battery for childhood psychopharmacology research by the National Institute of Mental Health.

ADD-H Adolescent Self Report Scale (ASRS). This rating scale is completed by the adolescents. It is similar to the CPRS-R, and is based on a Likert scale with many of the questions derived from the CPRSR (Couriers, 1997).

Peabody Picture Vocabulary Test-Ill (PP VT-III) . The PPVT-III was included as a screening measure to ensure that all participants were within an average intellectual and cognitive range. This is a standardized measure used regularly by school systems (Dunn & Dunn, 1997). This test requires the adolescent to listen to a word and choose from four pictures the one that best represents the meaning of the word. The PPVT-III has a mean of 100 and a standard deviation of 15. The PPVT-III has been shown to correlate with the WISC-R verbal IQ score at .81 (Smith, Smith, & Dobbs, 1991). It correlates .75 with the WISC-R vocabulary subscale (Carajal, Hayes, Miller, Wiebe, & Weaver, 1993).

Wide Range Achievement Test-Revised (WRAT-R). This test was used as a screening measure both to assess general cognitive level and presence of learning disabilities. It is another standardized measure used frequently in the school system to assess spelling, arithmetic, and reading (Wilkinson, 1984). Christopher, Giuliani, Holte, and Beaman (1989) found that the WRAT-R correctly classified 79% of students who had learning disabilities as compared with students who were classified as ineligible for special services.

Dependent Measures

Wisconsin Card Sorting Test (WCST). The WCST is a neuropsychological test sensitive to frontal lobe dysfunction. It is a widely used neuropsychological assessment tool published by Psychological Assessment Resources, Inc. It has been used as a test of perseveration and to assess the ability to sort cards according to class membership. Research on the WCST has substantiated its utility as a test sensitive to frontal lobe dysfunction. Researchers have found that individuals with frontal lobe damage committed more perseverative errors than did non-frontal lobe damaged or control groups (Drewe, 1974; Robinson, Heaton, Lehman, & Stilson, 1980). Axelrod, Goldman, Heaton, and Curtiss (1996) found that the WCST was able to discriminate normals from frontal lobe patient groups. Brain imaging studies using positron emission tomography (PET) have shown that the WCST produces increased regional cerebral blood flow in the prefrontal cortex with normal volunteers (Berman, Ostreem, Randolph, & Gold, 1995; Rezia et al., 199 3). The WOST has interrater reliability ranging from .75 to .97 with novice scorers who did not have previous experience in scoring the WOST (Heaton, Chelune, Tally, Kay, & Curtiss, 1993).

Stroop Color and Word Test (SCWT). This is another test sensitive to frontal lobe dysfunction. It is standardized and has been used frequently for this purpose. It tests the ability to separate word- and color-naming stimuli. Differences in performance between participants with frontal lesions and controls have been found using the SCWT (Mattson & Levin, 1990; Vendrell et al., 1995). The utility of the SCWT as a measure of frontal lobe dysfunction has also been examined using imaging techniques. Bench et al. (1993) tested healthy volunteers with the SCWT utilizing PET and found that the SCWT activated frontal areas of the brain.

Purdue Pegboard (PP). This test was used as the control task. Whereas the other tests examined frontal lobe functioning, this test did not. This test assesses motor functioning (Golden, 1990), requiring the participant to place pegs in two rows on a pegboard. Participants did this first with their left hand, then the right hand, and finally with both hands. The resultant score equals the number of pegs placed in each trial.

Procedure

Informed consent and children's assent procedures followed the ethical guidelines of the American Psychological Association. The sponsoring university's institutional review board approved the project.

Initial screening began with contact of the parent(s) of the potential participant. The investigator verbally described the proposed study and ascertained if the parent was willing to permit the child to participate. If so, further information was obtained to determine if the child would meet the basic criteria. Finally, a convenient time was arranged to meet with the parent and adolescent.

Each parent and child served individually in a single study session which began with the investigator explaining the purpose of the study to both the adolescent and the parent or guardian-that the investigator was trying to better understand ADHD by studying how persons with and without ADHD perform different tasks. After answering any questions, written informed consent was obtained from the parent/guardian and both verbal and written assent were obtained from the adolescent. Participants were reminded that they could stop the study at any time.

The study began with the parent/guardian completing the CPRS-R. The participant then completed the ADD-H Adolescent Self Report Scale, PPVT-III, and WRAT-R screening instruments. Following the screening measures, the WCST, SCWT, and the Purdue Pegboard were administered. Presentation was counterbalanced to control for order effects. Instructions followed the respective test manuals. Testing required 90-105 minutes. No participant appeared or reported being uncomfortable during the study. All enrolled participants completed the study.

After testing, parents and participants were debriefed. Questions were solicited, and the parents also were encouraged to contact the investigator in the future if they had any further questions or comments. A day after each study session, the investigator initiated a follow-up contact. At the completion of the study, the investigator contacted all parents and provided a synopsis of the findings.

RESULTS

As each instrument and each instrument's scales are considered as independent indices, independent groups t tests were performed on each of the neuropsychological measures comparing the performance of the ADHD group with the controls. Levene's Test for Equality of Variances was performed to determine the homogeneity of the groups. If equal variances could not be assumed for the two groups, the t test was interpreted accordingly.

The Purdue Pegboard was included to serve as a control task which yielded three scores: left hand, right hand, and both hands. Means and standard deviations of the scores for the two groups on the control task are presented in Table 2. All participants scored within the normal range. No between-groups differences were found on any of the scores for this task, supporting the assumption of group equivalence on psychomotor function.

Stroop Color and Word Test and Wisconsin Card Sorting Test means and standard deviations of the scores for the two study groups are presented in Table 3. The SCWT yielded four different scores. The word score is the number of items completed on the first page of the test; no differences were found on this score. The color score is the number of items completed on the second page of the test. The ADHD group scored lower than the control group, t(18) = 2.71, p < .014; [[eta].sup.2] was .35. The color/word score is the number of items completed on the third page of the test. The ADHD group scored lower than the control group, t(18) = 4.ll,p <.001; [[eta].sup.2] was .76. The last score for the Stroop Color and Word Test was the interference score which was calculated for each participant by computing a predicted color/word score based on performance on the word and color trials, then comparing the predicted color/word score with the actual color/word score. The higher the interference score, the more resistance to i nterference. The ADHD group was more vulnerable to interference, t(18) = 3.305, p < .004; [[eta].sup.2] was .51.

The WCST yielded eight different scores. The number of overall trials completed for the WCST varied among participants. As a result, percentages were calculated and compared for many of the scores. The scores that were examined included: trials administered, total number correct, percent of errors, percent of perseverative responses, percent of perseverative errors, percent of nonperseverative errors, number of categories completed, and failure to maintain set. Differences between the ADHD group and control group were not found on the following scores: trials administered, total number correct, percent of errors, percent of nonperseverative errors, and failure to maintain set. Performance on the percent of perseverative responses indicated that the ADHD group made more perseverative responses, t(18) = 2.298, p < .034; [[eta].sup.2] was .26. The ADHD group made more perseverative errors, t(18) = 2.403, p < .027; [[eta].sup.2] was .28. The number of categories completed yielded t(18) = 3.657,p <.005, indicating th at the ADHD group completed fewer categories than the control group; [[eta].sup.2] was .62.

DISCUSSION

The results of the current study show that the ADHD group performed significantly worse than the control group on tasks sensitive to frontal lobe dysfunction. On the WCST, perhaps the most widely used assessment tool in examining frontal lobe functioning, the ADHD group made more perseverative responses and perseverative errors, and completed fewer categories.

Compared to their controls, the ADHD group also performed significantly worse on the color, color/word, and interference scores of the SCWT. It is the interference score that is important to the exploration of the study. The interference score calculates a predicted color/word score for each subject based on word score and color score. The predicted score is then compared with the actual color/word score to determine an interference score. The ADHD group was more susceptible to effects of task-irrelevant information as evidenced by their interference scores.

The Purdue Pegboard was included in the study as a control task. The task assesses general neuropsychological functioning not associated with the frontal lobes. No group differences were found on this task. This refers to the idea that ADHD adolescents are not performing poorer than controls on the frontal lobe measures due to general neuropsychological dysfunction, but rather because of a specific frontal lobe deficit.

A weakness of the study is that a simple control measure was utilized rather than a full neuropsychological assessment. The control measure was used in order to rule out the possibility that differences on the WCST and SCWT might be due to general impairment. A full neuropsychological evaluation would have been best suited to do this but was not possible.

The current study supports the work of Seidman et al. (1997). They found significant differences on both the SCWT and the WCST in adolescents with ADHD as compared with non-ADHD adolescents. The current study and the work of Seidman et al. (1997) combine to provide a consistent report of frontal lobe functioning in adolescents with ADHD.

The current study examined frontal lobe functioning in adolescents using neuropsychological assessment. The results show differences between the ADHD group and control group. Information regarding what area or areas are specifically dysfunctional in the frontal lobes of the adolescent with ADHD still remains unclear. Although differences were found in frontal lobe functioning between the two groups, it cannot be determined here whether frontal lobe dysfunction in adolescents with ADHD stems from altered frontal lobe structure or altered functioning of the frontal lobes.

Given the current study and other recent studies, an area of functioning that might warrant future research would be the dorsolateral area of the frontal lobes as well as the dorsolateral prefrontal circuit of functioning. The WCST and SCWT have been suggested to specifically probe the dorsolateral area of the prefrontal cortex (Milner, 1963; Fuster, 1997; Kolb & Whishaw, 1990). Fuster (1997) believes the dorsolateral area is responsible for attention and planning. Difficulties in planning and short-term memory tend to be prevalent in dorsolateral syndromes. Fisher (1998) discusses the dorsolateral prefrontal circuit which she believes originates in Brodmann areas 9 and 10 commencing on the lateral surface of the anterior frontal lobe. Connections project to the caudate nucleus and substantia nigra. Fisher discusses both direct and indirect pathways, and contends that the dorsolateral prefrontal circuit is responsible for executive functioning and that damage is characterized by perseveration and general lac k of initiation. Others have also claimed that the dorsolateral prefrontal subsystem is responsible for executive functions (Cummings, 1993; Malloy & Richardson, 1994; Levine, Parks, & Prueitt, 1993).

Recently, studies have examined the caudate nucleus since inputs from it are received in the dorsolateral circuit. Mataro, Garcia-Sanchez, Junque, and Estevez-Gonzales (1997) used magnetic resonance imaging to measure the caudate nucleus in adolescents with ADHD and found that the ADHD group had a larger right caudate nucleus area than did the control group. They found that in control subjects, larger caudate nucleus areas were associated with a worse performance on tests of attention. Others have also used brain imaging techniques to study the caudate nucleus in individuals with ADHD, although the findings have not been consistent (Filipek et al., 1997; Castellanos et al., 1994; Hynd et al., 1993).

Future research should aim toward further investigation of the dorsolateral prefrontal subsystem of the frontal lobes in individuals with ADHD. It would be useful if proposed circuits of the dorsolateral prefrontal subsystem could be evaluated. Brain imaging techniques would be useful in illuminating circuits of functioning within the frontal lobes of the individual with ADHD. The use of cognitive tasks such as the WCST and SCWT during functional brain imaging may provide researchers with a cohesive picture of deficits in the ADHD individual. Additionally, longitudinal studies of behavioral neuropsychological functioning in adults with ADHD are needed. This would provide a complete investigation of neuropsychological deficits in attention deficit disorder across the lifespan, which would aid in a better understanding of the disorder.

Table 1

Means (and Standard Deviations) for the ADHD Group (n = 10) and the
Control Group (n = 10) on the Screening Tests

                                      ADHD                Control
                                  M       (SD)         M    (SD)

Peabody Picture Vocabulary      98.9     (9.4)      100.6   (7.1)
Test-III

Conners Parent Rating
Scale-Revised

  Hyperactivity Index           69.0    (13.9)       48.4   (4.0)
  ADHD Index                    69.6     (4.5)       51.4   (4.5)

Adolescent Self-Report Scale

  Hyperactivity Index           61.8     (8.3)       43.0   (6.4)
  ADHD Index                    62.6     (7.4)       52.3   (7.4)
Table 2

Means (and Standard Deviations) for the ADHD Group (n = 10) and the
Control Group (n = 10) on the Purdue Pegboard Control Task

                    ADHD                Control
                M      (SD)          M     (SD)       t       p

Right Hand    13.3    (1.6)        13.3   (1.8)     .00       n.s.
Left Hand     12.8    (1.6)        13.1   (1.4)     .45       n.s
Both Hands    10.7    (1.8)        10.2   (1.1)     .05       n.s.
Table 3

Means (and Standard Deviations) for the ADHD Group (n = 10) and the
Control Group (n = 10) on the Stroop Test and the Wisconsin Card
Sort Test

                                     ADHD                 Control
                                  M      (SD)            M    (SD)

Stroop Color Word Test

  Word Score                   79.9    (20.6)         87.6  (14.1)
  Color Score                  50.7    (14.1)         65.4   (9.9)
  Color/Word Score             30.8     (8.4)         44.1   (5.9)
  Interference Score            1.0     (4.3)          6.9   (3.7)

Wisconsin Card Sort Test

  Trials Administered         116.5    (18.7)        100.1  (20.9)
  Total Number Correct         70.6    (14.5)         72.3  (12.7)
  % Errors                     37.6    (16.8)         25.9  (13.9)
  % Perseverative Responses    22.3    (13.4)         11.5   (6.5)
  % Perseverative Errors       21.4    (12.1)         11.2   (5.9)
  % Nonperseverative Errors    15.8     (8.9)         12.7   (4.7)
  # Categories Completed        4.1     (1.5)          5.9    (.3)
  Failure to Maintain Set       1.4      (.9)          1.6   (1.0)


                                t       p

Stroop Color Word Test

  Word Score                 1.61      n.s
  Color Score                2.70      .01
  Color/Word Score           4.11      .001
  Interference Score         3.31      .004

Wisconsin Card Sort Test

  Trials Administered        1.85      n.s
  Total Number Correct        .28      n.s
  % Errors                   1.70      n.s
  % Perseverative Responses  2.30      .03
  % Perseverative Errors     2.40      .02
  % Nonperseverative Errors   .97      n.s
  # Categories Completed     3.66      .005
  Failure to Maintain Set     .85      n.s

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Portions of this study were supported by a Merit Review Grant from the Department of Veterans Affairs.

Whitney V. Reeve, Division of Psychology, Chapman University, Orange, California.

Reprint requests to Steven L. Schandler, Addiction Research Laboratory, Mail Stop 09 / 1514, Long Beach Veterans Affairs Health Care System, 5901 East Seventh Street, Long Beach, California 90822. Electronic mail may be sent via Internet to schandle@chapman.edu.

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