Microsoft Word - Vol10_CalePalmer_AVK#2AF7AD.doc 38 Graduate Student Journal of Psychology Copyright 2008 by the Department of Counseling & Clinical Psychology 2008, Vol. 10 Teachers College, Columbia University ISSN 1088-4661 Executive Functioning in Schizophrenia: The Contributions of Attention, Working Memory, Processing Speed, and General Intelligence Cale D. Palmer University of Hawaii at Manoa Elaine Heiby University of Hawaii at Manoa Daryl Fujii University of Hawaii at Manoa Velma Kameoka University of Hawaii at Manoa The purpose of this study was to assess the degree to which executive functioning performance may be associated with indices of attention, working memory, processing speed, and general in- telligence in 45 individuals with schizophrenia from a multicultural sample. It was hypothesized that relatively higher performances on measures of these cognitive processes would be positively associated with higher executive functioning performance, as measured by the Wisconsin Card Sorting Test (WCST). Contrary to expectations, results indicated that attention, working memory, and processing speed did not significantly correlate with executive functioning performance. However, Wechsler Adult Intelligence Scale, Third Edition (WAIS-III) Full-Scale IQ scores did significantly correlate with WCST performance, suggesting that general intellectual deficits may underlie executive functioning impairments in schizophrenia. Schizophrenia is a psychotic disorder often character- ized by delusions and hallucinations (American Psychiatric Association, 2000). Schizophrenia may also be conceptu- alized as a chronic neurocognitive disorder with varied levels of functioning and symptom presentations, including deficits in attention, memory, processing speed, and execu- tive functioning. Such cognitive deficits appear to predate clinical symptoms (Murray, 1994), remain relatively stable after the onset of schizophrenia (Heaton et al., 2001; Hoff et al., 1999; Rund, 1998), and remain stable regardless of baseline and changes in clinical state (Heaton et al., 2001). Deficits in cognitive functioning may be considered core symptoms of schizophrenia (Weickert et al., 2000) and have been associated with relapse and functional outcome (Chen et al., 2005; Green, Kern, Braff, & Mintz, 2000; Sergi, Kern, Mintz, & Green, 2005; Woonings, Appelo, Kluiter, Slooff, & van den Bosch, 2002). In addition, func- tional outcome may be more reliably related to cognitive impairment than positive symptomatic variables (Axelrod, Goldman, Tompkins, & Jiron, 1994). One such cognitive deficit that has been widely studied in individuals with schizophrenia is executive functioning, a broad term comprised of several components, including Correspondence and reprint requests to Cale Palmer at Depart- ment of Psychology, University of Hawaii at Manoa, 2430 Campus Rd., Honolulu, HI 96822. E-mail: cale@hawaii.edu. determining what one wants or needs, conceptualizing the future realization of that want or need, identifying and or- ganizing the steps and resources required to achieve the goal, weighing alternatives and making choices, and the translation of a plan into action via sequences of complex behavior in an orderly fashion (Lezak, 1995). Executive functioning has also been described as involving volition, planning, purposive action, and self-monitoring of behavior (Green et al., 2000; Lezak, 1995), which enable the per- formance of complex and high-level tasks. Lezak (1995) has characterized executive abilities as “those capacities that enable a person to engage successfully in independent, purposive, self-serving behavior” (p. 42). Maintaining or shifting mental sets, establishing goals, and planning are crucial aspects of executive functioning (Stuss & Benson, 1986) and can be measured by neuropsychological tests specifically designed to assess executive functioning. One of the most established and widely used measures of executive functioning is the Wisconsin Card Sorting Test (WCST; Berg, 1948; Grant & Berg, 1948; Heaton, Chelune, Talley, Kay, & Curtiss, 1993), a complex task designed to assess the ability to shift cognitive strategies in response to changing environmental contingencies. The test requires subjects to perceive and abstract relevant attributes and ignore irrelevant ones, to engage in hypothesis genera- tion and testing, and to abandon irrelevant hypotheses or principles when necessary (King & Snow, 1981). Success- ful WCST performance is thought to involve strategic planning, organized searching, goal-oriented behavior, modulation of impulsive responding, and the ability to use EXECUTIVE FUNCTIONING IN SCHIZOPHRENIA 39 environmental feedback to shift cognitive sets (Spreen & Strauss, 1998). In individuals with schizophrenia, performances on the WCST are often impaired relative to normal and psychiat- ric controls (Beatty, Jocic, Monson, & Katzung, 1994; Everett, Lavoie, Gagnon, & Gosselin, 2001; Ilonen et al., 2000; Johnson-Selfridge & Zalewski, 2001; Metz, Johnson, Pliskin, & Luchins, 1994; Reed, Harrow, Herbener, & Martin, 2002), and some of the research seeking to explain the WCST performance impairment associated with schizophrenia has centered on correlations with intellectual or cognitive abilities, such as attention and working mem- ory, measured by tests commonly used in neuropsychologi- cal batteries. Results from these studies, however, have often been unclear or conflicting, and much remains to be known about the specific cognitive processes involved in WCST performance and what processes contribute to the relatively impaired WCST performance associated with schizophrenia. Some researchers, for example, have suggested that attention may underlie WCST performance (Perry, Potterat, & Braff, 2001; Stratta, Mancini, Mattei, Casacchia, & Rossi, 1994). Differences between individuals with schizo- phrenia in an inpatient setting and controls on WCST per- formance may be eliminated after controlling for attention using analysis of covariance (Kenny & Meltzer, 1991), and attention training may remediate WCST deficits (Lopez- Luengo & Vazquez, 2003). Other studies, however, suggest that attention may be insufficient in explaining WCST per- formance or have found no significant correlation between WCST performance and attention (Chen et al., 1997; Dela- hunty, Morice, & Frost, 1993; Frost et al., 1991; Goldberg, Weinberger, Berman, Pliskin, & Podd, 1987; Greve, In- gram, & Bianchini, 1998). Similarly, while some studies have found evidence of an association between working memory and executive functioning in schizophrenia (Glahn, Cannon, Gur, Ragland, & Gur, 2000; Gold, Car- penter, Randolph, Goldberg, & Weinberger, 1997; Gooding & Tallent, 2002; Morice & Delahunty, 1996; Stone, Gab- rieli, Stebbins, & Sullivan, 1998), others have not (Bellack, Mueser, Morrison, Tierney, & Podell, 1990; Goldman, Ax- elrod, & Tompkins, 1992; Greve et al., 1998; Stratta et al., 1997; Vollema, Geurtsen, & van Voorst, 1995). Thus, while attention and working memory have yet to fully ex- plain WCST performance impairments, many studies do suggest some degree of impairment, and differences in sample composition and instruments across studies likely contribute to inconsistent findings. In addition, few studies have directly assessed the association between attention and executive functioning, and of those that have, many studies relied on visual rather than auditory stimuli when measuring attention. As individuals with schizophrenia may be relatively more impaired on auditory measures of attention (Borgaro et al., 2003; Mirsky, Yardley, Jones, Walsh, & Kendler, 1995; Mussgay & Hertwig, 1990), a more sensitive measure of impairment may yield more con- sistent, significant results. Research appears relatively more limited with regard to assessing processing speed in schizophrenia and its po- tential contribution to impaired WCST performance. Indi- viduals with schizophrenia have been found to have im- paired processing speed (Egeland et al., 2003; Hong et al., 2002; Saccuzzo & Braff, 1981), and this impairment may result in a disrupted flow of information as new stimuli enter before other stimuli have transferred (Felsten & Was- serman, 1980; Saccuzzo & Braff, 1981). This slowed proc- essing speed may cause individuals with schizophrenia to lose information before being able to use it (Brebion et al., 2000; Hartman, Steketee, Silva, Lanning, & Andersson, 2003), and thus may contribute to impaired WCST per- formance. However, this hypothetical association has yet to be directly assessed. Finally, it is also possible that WCST performance im- pairments associated with schizophrenia may be due to deficits in generalized intelligence (Laws, 1999). While some argue that WCST performance may not be fully ac- counted for by IQ scores (Elliott, McKenna, Robbins, & Sahakian, 1995; Morice, 1990), many studies have demon- strated significant associations between WCST and IQ scores (Dieci et al., 1997; Gold et al., 1997; Goldberg, Kel- soe, & Weinberger, 1988; Ilonen et al., 2000; Laws, 1999; Seidman et al., 1991), as well as IQ estimates (Koren et al., 1998; Sweeney, Kelip, Haas, Hill, & Weiden, 1991) in in- dividuals with schizophrenia. One study reported that IQ scores account for approximately 40% of the variance in WCST performance (Gold et al., 1997). Additional support for a possible association between IQ and WCST performance has been found in several studies that compared groups of individuals with different levels of IQ or WCST performance impairment. For exam- ple, in a study by Goldstein, Beers, and Shemansky (1996), individuals with poor WCST performance had significantly lower IQ subtest scores compared to those individuals that did not exhibit WCST performance impairment. Weickert et al. (2000), also found relatively impaired WCST per- formance in individuals with schizophrenia with lower IQ estimates. In the same study, a minority of patients with schizophrenia demonstrated an average level IQ, and, to a lesser degree, they too demonstrated some WCST perform- ance impairment compared to normal controls (Weickert et al., 2000). Similarly, Kremen, Seidman, Faraone, and Tsu- ang (2001), found that based on WCST and Visual-Verbal Test scores (Feldman & Drasgow, 1981), abstraction- executive function was relatively more impaired in indi- viduals with schizophrenia who had an estimated low- average IQ compared to those with average IQ, although both groups demonstrated impaired abstraction-executive function compared to IQ-matched normal controls. Finally, in a study by Dieci et al. (1997), WCST per- formance was not able to better discriminate healthy con- trols from individuals with schizophrenia when compared to IQ scores, suggesting that WCST may not represent a pronounced deficit separate from a general intellectual deficit. Not all studies, though, have found a significant PALMER, HEIBY, FUJII & KAMEOKA 40 association; in a study by Morice and Delahunty (1996), the correlation between WCST perseverative errors and IQ was not statistically significant (r = -0.34), and WCST per- formance impairments appeared to be present independent of any apparent deterioration in general intelligence from premorbid levels. However, this study used a small sample size (n = 17) and may also have been unusual in that while IQ scores were relatively lower compared to normal con- trols, the mean IQ for the schizophrenia group was still in the average range. Furthermore, as schizophrenia is a het- erogeneous disorder, patterns of cognitive impairment may differ when looking at different levels of IQ (Weickert et al., 2000). Overall, a review of the literature indicates some equivocal and contradictory findings, and not much is known about the actual processes that contribute to the poor WCST performance by persons with schizophrenia. As current research has yet to fully explain WCST per- formance impairments, the purpose of this study was to examine some of the hypothesized underlying cognitive processes that may contribute to the relatively impaired executive functioning of individuals with schizophrenia in a multicultural sample. To this end, measures of attention, working memory, processing speed, and general intelli- gence were correlated with executive functioning perform- ance, as measured by the Wisconsin Card Sorting Test. It was hypothesized that relatively higher performances on measures of these cognitive processes would be positively associated with higher executive functioning performance. Method Participants Participant data was obtained from archived neuropsy- chological reports from Hawaii State Hospital, a state fo- rensic and psychiatric hospital serving a multicultural population. Subjects had been referred for neuropsy- chological testing, were found to have adequate vision and hearing, and completed a neuropsychological battery. A review of reports from April 1998 to August 2002 yielded 54 subjects. After excluding 9 subjects due to missing data, a total of 45 subjects remained in the study. At the time of their evaluation, individuals were either currently in an inpatient setting at Hawaii State Hospital (n = 43), in an outpatient setting (n = 1), or in community placement awaiting trial (n = 1). There were 37 (82.2%) males and 8 (17.8%) females. The average age was 36.42 (SD = 8.25), and the average number of years of education was 10.76 (SD = 2.10). Approximately half of the sample was of mixed ethnicity (n = 23, 51.1%). Other represented ethnic- ities included Caucasian (n = 8, 17.8%), Pacific Islander (n = 7, 15.6%), Asian American (n = 5, 11.1%), and African American (n = 2, 4.4%). Of those of mixed ethnicity, common ethnic combinations included individuals classi- fied as “part Hawaiian” (n = 8, 17.8% of total sample), Caucasian and Pacific Islander (n = 3, 6.7%), and Asian American and Caucasian (n = 2, 4.4%). Within the sample, 33 (73.3%) individuals had a pri- mary diagnosis of schizophrenia, and 12 (26.7%) had a diagnosis of schizoaffective disorder. A comorbid sub- stance abuse or dependence diagnosis was found in a ma- jority (n = 29, 64.4%) of the participants. Drug use in- cluded alcohol (n = 18, 40%), marijuana (n = 12, 26.7%), cocaine (n = 7, 15.6%), methamphetamine (n = 4, 8.9%), amphetamine (n = 1, 2.2%), inhalants (n = 2, 4.4%), heroin (n = 1, 2.2%), PCP (n = 1, 2.2%), sedatives (n = 1, 2.2%), and unspecified polysubstance use (n = 7, 15.6%). Measures Indicators of general intelligence, working memory, and processing speed were derived from Wechsler Adult Intelligence Scale – Third Edition (WAIS-III; Wechsler, 1997) Full-Scale IQ, Working Memory Index, and Proc- essing Speed Index scores, respectively. The Working Memory Index consists of scores on the Arithmetic, Digit Span, and Letter-Number Sequencing subtests. The Proc- essing Speed Index consists of the Symbol Search and Digit Symbol-Coding subtests. The indicator of the cogni- tive process of attention was derived from the total number of errors on the Continuous Performance Test of Attention (CPTA-I), an auditory test of attentional vigilance (Cice- rone, 1997; Nuechterlein, Buchsbaum, & Dawson, 1994). The Wisconsin Card Sorting Test (WCST) Categories Completed score yielded a measure of executive function- ing. Procedure Data collection was based on an archived set of neuro- psychological reports, which included demographic infor- mation, psychiatric diagnoses, and cognitive test scores. Participants were administered standard versions of neuro- psychological tests by trained hospital staff, from which scores of cognitive and intellectual functioning were de- rived. Psychiatric diagnoses were determined from multidisciplinary group meetings, which routinely included hospital staff from psychiatry, psychology, nursing, and additional departments. Statistical Analyses Correlational analyses assessed the degree to which scores of attention, working memory, processing speed, and general intellectual functioning were associated with executive functioning. Statistical significance was set at the p 0.05 level. A data transformation was also conducted on CPTA-I scores due to non-normal skewness and kurto- sis; in accordance with Tukey’s ladder of powers (1977), a square root transformation was able to successfully ap- proximate normal skewness and kurtosis values for this EXECUTIVE FUNCTIONING IN SCHIZOPHRENIA 41 distribution. All other variables demonstrated normal dis- tributions. The contribution of each WAIS-III subtest to the variance of executive functioning was not computed due to the sample size. Results Individuals with schizophrenia demonstrated impair- ment on cognitive tests, including the CPTA-I total number of errors (M = 33.93, SD = 22.53), WAIS-III Working Memory Index (M = 78.67, SD = 11.90), WAIS-III Proc- essing Speed Index (M = 78.36, SD = 9.65), WAIS-III Full- Scale IQ (M = 78.69, SD = 10.18), and WCST Categories Completed (M = 2.91, SD = 1.84). Zero-order correlations between executive functioning scores and measures of at- tention (r = -0.23, p = 0.135), working memory (r = 0.18, p = 0.245), and processing speed (r = 0.21, p = 0.177) yielded only non-significant associations, which did not support the hypothesis that measures of attention, working memory, and processing speed would help explain or ac- count for deficits in WCST performance in schizophrenia. However, executive functioning was significantly corre- lated with general intellectual functioning (r = 0.39, p = 0.009). Thus, the hypotheses of this study were partially supported. A post hoc analysis also found that even after controlling for attention, working memory, and processing speed, executive functioning was still significantly corre- lated with general intellectual functioning (r = 0.36, p = 0.020). Discussion It was hypothesized that relatively higher perform- ances on measures of attention, working memory, process- ing speed, and general intellectual functioning would be positively associated with higher executive functioning performance, as measured by the Wisconsin Card Sorting Test (WCST). Contrary to expectations, results indicated that the specific cognitive processes of attention, working memory, and processing speed did not significantly corre- late with executive functioning performance. However, scores of general intellectual functioning did significantly correlate with WCST performance, even after controlling for attention, working memory, and processing speed. These results suggest that general intellectual deficits may underlie executive functioning impairments in schizophre- nia. The results of this study appear consistent with find- ings that IQ often correlates with and can often be used to predict performance on a wide variety of neuropsychologi- cal tests (Diaz-Asper, Schretlen, & Pearlson, 2004). Even in healthy, non-clinical samples, IQ scores may be signifi- cantly associated with WCST performance in adults (Diaz- Asper et al., 2004; Heaton, 1981) and children (Arffa, Lovell, Podell, & Goldberg, 1998; Chelune, & Baer, 1986), although correlations appear more modest than in clinical samples (Heaton, 1981). However, while general intellec- tual functioning is often thought to be relatively stable, remediation studies indicate that the deficits associated with schizophrenia with respect to WCST performance do not appear wholly unremediable (Bellack et al., 1990; De- lahunty et al., 1993; Metz et al., 1994; Perry et al., 2001; Vollema et al., 1995; Young & Freyslinger, 1995). In addi- tion, it has been shown that the skills measured on com- monly used IQ tests are trainable (Staats, 1989; Staats, 1990; Staats & Burns, 1981). Thus, the results of this study may also suggest the importance of examining cognitive processes that are associated with each WAIS-III (Wechsler, 1997) subtest, particularly those not included in the computation of Working Memory and Processing Speed Index scores. Perceptual organization and verbal comprehension, for example, may contribute to WCST performance. Scores from individual subtests that compose the WAIS-III Verbal Comprehension and Perceptual Organization Index scores were not able to be analyzed in this study due to a small sample size. However, the skills necessary for each of these subtests may also be important for WCST performance. For example, skills measured by WAIS-III verbal subtests not directly analyzed in this study include distinguishing es- sential from non-essential detail, using abstract symbols, and abstract reasoning (Groth-Marnat, 2003). Planning ability, attention to detail, accurate responding to visual- spatial material, visual-spatial reasoning, and visual alert- ness and concentration are other skills measured by WAIS- III performance subtests (Groth-Marnat, 2003) not directly analyzed in this study. Furthermore, additional WAIS-III score configurations, such as Horn’s (1985; Kaufman & Lichtenberger, 2002) Broad Visualization, as well as Ban- natyne’s (1974) Spatial Abilities, involve groupings of subtests not included in the Working Memory and Proc- essing Speed Index scores. As WCST performance also involves the use of visual cues, reasoning, and planning, these skills may prove to be significant contributors to un- derstanding WCST performance impairment. It is also possible that cognitive processes not as ex- plicitly measured by the WAIS-III may be impaired in schizophrenia and factor into impaired WCST perform- ance. Cognitive processes, for example, such as concept formation and attribute identification (Perrine, 1993) or insight and metacognition (Koren et al., 2004) may better account for WCST performance impairments in individuals with schizophrenia. In terms of treatment implications, the identification of these potentially important cognitive proc- esses may translate into improved WCST performance and executive functioning in individuals with schizophrenia. However, based on the results of this study, it would appear that a specific focus on improving attention, working mem- ory, and processing speed may not carry over to improved WCST performance within this population of individuals with schizophrenia. The results of this study may be limited in their gener- alizability. First, the sample of the present study was drawn from a relatively understudied multicultural population PALMER, HEIBY, FUJII & KAMEOKA 42 (Leong, 1989) living in the Hawaiian Islands and thus con- sisted of a relatively large proportion of individuals of Asian Pacific Islander descent. As such, related factors that were not included in the archived data used in this study (e.g., language proficiency, acculturation, familiarity with cognitive testing, etc.) may have impacted the statistical findings of this study. A review of the literature indicates that few studies have examined WCST performance defi- cits in ethnic minorities, and, in general, there is a need for more psychological studies on ethnic minorities (Sue, 1999). This appears particularly relevant as IQ scores vary across ethnic groups (Lynn, 1996; Suzuki & Valencia, 1997), and ethnic background may predict performance on neuropsychological tests (Gladsjo et al., 1999). Individuals from disadvantaged cultural groups may also have higher rates of schizophrenia (Eaton & Harrison, 2000) and thus be at more risk for cognitive impairment. A second characteristic of the sample that may have implications for generalization is the inclusion of subjects with dual diagnoses. Individuals with dual diagnoses are often excluded from neuropsychological studies, which may not be justified given that significant differences in WCST performance between non-affective psychotic pa- tients with and without a dual diagnosis of comorbid sub- stance use may not exist (Liraud & Verdoux, 2002). In ad- dition, the high degree of comorbid substance use in indi- viduals with schizophrenia (Regier et al., 1990) suggests that many studies to date have looked at only a small subset of the larger population of individuals with schizophrenia due to the exclusion of comorbid substance use. Comorbid substance use in this population may also be of great im- portance due to its association with poorer functional out- comes, more frequent hospitalizations, treatment non- compliance, a more severe course of the disorder, more severe symptomatology, and increased risk of suicide (Bartels et al., 1993; Jackson, Fein, Essock, & Mueser, 2001; Mueser, Bellack, & Blanchard, 1992). However, the research practice of combining data from individuals with different diagnoses invariably results in an increase in het- erogeneity and may interfere with targeting what cognitive processes may be important to consider for executive func- tioning performance and the impairment that may be asso- ciated with specific disorders. The interpretation of statisti- cal findings and the role that various cognitive processes may play in executive functioning in schizophrenia may have been clouded by the inclusion of dual diagnosis sub- jects. Further research examining potential differences be- tween individuals with schizophrenia with and without substance abuse problems may help clarify this issue and whether similar research in the future would benefit from the inclusion or exclusion of such dual diagnosis subjects. Several additional limitations of this study may be noted. Due to the correlational nature of the study, signifi- cant findings should not be interpreted as evidence of cau- sation. Also, several potentially relevant factors were not able to be addressed adequately by the archived data set, such as diagnostic reliability, medication use, symptom severity, and the reason for referral for neuropsychological testing. Executive functioning performance and its relation- ship to other cognitive processes may differ for individuals with schizophrenia who are stable and on medications compared to those with more active and severe symptoms. Future research may help to address these limitations and clarify what cognitive processes may help explain WCST performance in schizophrenia. Addressing potentially relevant factors such as medi- cation use and symptom severity, as well as measuring cognitive processes not addressed in this study, may illus- trate key aspects to understanding executive functioning impairment. A comparison of individuals with and without dual diagnoses may also shed light on the degree to which executive functioning impairment and its related cognitive processes may be affected by substance use and have to be taken into consideration. Furthermore, remediation studies with individuals with schizophrenia may provide the clear- est evidence of the best path to cognitive rehabilitation. References American Psychiatric Association (2000). Diagnostic and Statistical Manual of Mental Disorders (4 th ed., Text Re- vision). Washington, D. C.: American Psychiatric Asso- ciation. Arffa, S., Lovell, M., Podell, K., & Goldberg, E. (1998). Wisconsin Card Sorting Test performance in above aver- age and superior school children. Archives of Clinical Neuropsychology, 13, 713-720. Axelrod, B., Goldman, R., Tompkins, L., & Jiron, C. (1994). Poor differential performance of the Wisconsin Card Sorting Test in schizophrenia, mood disorder, and trau- matic brain injury. Neuropsychiatry, Neuropsychology, and Behavioral Neurology, 7, 20-24. Bannatyne, A. (1974). Diagnosis: A note on recategorization of the WISC scaled scores. Journal of Learning Disabili- ties, 7, 272-273. Bartels, S., Teague, G., Drake, R., Clark, R., Bush, P., & Noordsy, D. (1993). Substance abuse in schizophrenia: Service utilization and costs. Journal of Nervous and Mental Disease, 181, 227-232. Beatty, W. W., Jocic, Z., Monson, N., & Katzung, V. M. (1994). Problem solving by schizophrenic and schizoaf- fective patients on the Wisconsin and California Card Sorting Tests. Neuropsychology, 8, 49-54. Bellack, A. S., Mueser, K. T., Morrison, R. L., Tierney, A., & Podell, K. (1990). Remediation of cognitive deficits in schizophrenia. American Journal of Psychiatry, 147, 1650-1655. Berg, E. (1948). A simple objective technique for measuring flexibility in thinking. Journal of General Psychology, 39, 15-22. Borgaro, S., Pogge, D., DeLuca, V., Bilginer, L., Stokes, J., & Harvey, P. (2003). Convergence of different versions of the Continuous Performance Test: Clinical and scientific EXECUTIVE FUNCTIONING IN SCHIZOPHRENIA 43 implications. Journal of Clinical and Experimental Neu- ropsychology, 25, 283-292. Brebion, G., Smith, M., Gorman, J., Malaspina, D., Sharif, Z., & Amador, X. (2000). Memory and schizophrenia: Differential link of processing speed and selective atten- tion with two levels of encoding. Journal of Psychiatric Research, 34, 121-127. Chelune, G., & Baer, R. (1986). Developmental norms for the Wisconsin Card Sorting Test. Journal of Clinical and Experimental Neuropsychology, 8, 219-228. Chen, E., Hui, C., Dunn, E., Miao, M., Yeung, W., Wong, C., Chan, W., & Tang, W. (2005). A prospective 3-year longitudinal study of cognitive predictors of relapse in first-episode schizophrenic patients. Schizophrenia Re- search, 77, 99-104. Chen, E., Lam, L., Chen, R., Nguyen, D., Chan, C., & Wil- kins, A. (1997). Neuropsychological correlates of sus- tained attention in schizophrenia. Schizophrenia Research, 24, 299-310. Cicerone, K. D. (1997). Clinical sensitivity of four measures of attention to mild traumatic brain injury. The Clinical Neuropsychologist, 11, 266-272. Delahunty, A., Morice, R., & Frost, B. (1993). Specific cognitive flexibility rehabilitation in schizophrenia. Psy- chological Medicine, 23, 221-227. Diaz-Asper, C., Schretlen, D., & Pearlson, G. (2004). How well does IQ predict neuropsychological test performance in normal adults? Journal of the International Neuropsy- chological Society, 10, 82-90. Dieci, M., Vita, A., Silenzi, C., Caputo, A., Comazzi, M., Ferrari, G., Mezzetti, M., Tenconi, F., & Invernuizzi, G. (1997). Non-selective impairment of Wisconsin Card Sort Test performance in patients with schizophrenia. Schizo- phrenia Research, 25, 33-42. Eaton, W., & Harrison, G. (2000). Ethnic disadvantage and schizophrenia. Acta Psychiatrica Scandinavica, 102, 38- 43. Egeland, J., Rund, B., Sundet, K., Landrø, N., Asbjørnsen A., Lund, A., Roness, A., Stordal, K., & Hugdahl, K. (2003). Attention profile in schizophrenia compared with depression: Differential effects of processing speed, se- lective attention and vigilance. Acta Psychiatrica Scandi- navica, 108, 276-284. Elliott, R., McKenna, P., Robbins, T., & Sahakian, B. (1995). Neuropsychological evidence for frontostriatal dysfunction in schizophrenia. Psychological Medicine, 25, 619-630. Everett, J., Lavoie, K., Gagnon, J., & Gosselin, N. (2001). Performance of patients with schizophrenia on the Wis- consin Card Sorting Test (WCST). Journal of Psychiatry & Neuroscience, 26, 123-130. Feldman, M., & Drasgow, J. (1981). The Visual-Verbal Test. Los Angeles, CA: Western Psychological Services. Felsten, G., & Wasserman, G. (1980). Visual masking: Mechanisms and theories. Psychological Bulletin, 88, 329-353. Frost, B., Morice, R., Delahunty, A., Gulliver, S., Ryan, M., Frampton, G., Connolly, S., & Hunter, M. (1991). Neuro- cognitive and psychosocial rehabilitation of chronic schizophrenia: A clinical study. In W. Levick, B. Frost, W. Watson, & P. Pfister (Eds.), Brain Impairment: Pro- ceedings of the Fifteenth Brain Impairment Conference (pp. 49-57). Melbourne: Australian Society for the Study of Brain Impairment. Gladsjo, J., Schuman, C., Evans, J., Peavy, G., Miller, S., & Heaton, R. (1999). Norms for letter and category fluency: Demographic corrections for age, education, and ethnicity. Assessment, 6, 147-178. Glahn, D. C., Cannon, T. D., Gur, R. E., Ragland, D., & Gur, R. C. (2000). Working memory constrains abstrac- tion in schizophrenia. Biological Psychiatry, 47, 34-42. Gold, J. M., Carpenter, C., Randolph, C., Goldberg, T. E., & Weinberger, D. R. (1997). Auditory working memory and Wisconsin Card Sorting Test performance in schizophre- nia. Archives of General Psychiatry, 54, 159-165. Goldberg, T. E., Kelsoe, J. R., & Weinberger, D. R. (1988). Performance of schizophrenic patients on putative neuro- psychological tests of frontal lobe function. International Journal of Neuroscience, 42, 51-58. Goldberg, T. E., Weinberger, D. R., Berman, K. F., Pliskin, N. H., & Podd, M. H. (1987). Further evidence for de- mentia of the prefrontal type in schizophrenia? Archives of General Psychiatry, 44, 1008-1014. Goldman, R. S., Axelrod, B. N., & Tompkins, L. M. (1992). Effect of instructional cues on schizophrenic patients’ per- formance on the Wisconsin Card Sorting Test. American Journal of Psychiatry, 149, 1718-1722. Goldstein, G., Beers, S. R., & Shemansky, W. J. (1996). Neuropsychological differences between schizophrenic patients with heterogeneous Wisconsin Card Sorting Test performance. Schizophrenia Research, 21, 13-18. Gooding, D. C., & Tallent, K. A. (2002). Spatial working memory performance in patients with schizoaffective psy- chosis versus schizophrenia: A tale of two disorders? Schizophrenia Research, 53, 209-218. Grant, D., & Berg, E. (1948). A behavioral analysis of de- gree of impairment and ease of shifting to new responses in a Weigl-type card sorting problem. Journal of Experi- mental Psychology, 39, 404-411. Green, M. F., Kern, R. S., Braff, D. L., & Mintz, J. (2000). Neurocognitive deficits and functional outcome in schizo- phrenia: Are we measuring the “right stuff”? Schizophrenia Bulletin, 26, 119-136. Greve, K. W., Ingram, F., & Bianchini, K. J. (1998). Latent structure of the Wisconsin Card Sorting Test in a clinical sample. Archives of Clinical Neuropsychology, 13, 597- 609. Groth-Marnat, G. (2003). Handbook of Psychological As- sessment (4 th ed.). Hoboken: Wiley. Hartman, M., Steketee, M. C., Silva, S., Lanning, K., & Andersson, C. (2003). Wisconsin Card Sorting Test per- formance in schizophrenia: The role of working memory. Schizophrenia Research, 63, 201-217. PALMER, HEIBY, FUJII & KAMEOKA 44 Heaton, R. K. (1981). Wisconsin Card Sorting Test Manual. Odessa, FL: Psychological Assessment Resources. Heaton, R. K., Chelune, G. J., Talley, J. L., Kay, G. G., & Curtiss, G. (1993). Wisconsin Card Sorting Test Manual, Revised and Expanded. Odessa, FL: Psychological As- sessment Resources. Heaton, R. K., Gladsjo, J. A., Palmer, B. W., Kuck, J., Mar- cotte, T. D., & Jeste, D. V. (2001). Stability and course of neuropsychological deficits in schizophrenia. Archives of General Psychiatry, 58, 24-32. Hoff, A. L., Sakuma, M., Wieneke, M., Horon, R., Kushner, M., & DeLisi, L. E. (1999). Longitudinal neuropsy- chological follow-up study of patients with first-episode schizophrenia. American Journal of Psychiatry, 156, 1336-1341. Hong, K. S., Kim, J. G., Koh, H. J., Koo, M. S., Kim, J. H., Lee, D., & Kim, E. (2002). Effects of risperidone on in- formation processing and attention in first-episode schizo- phrenia. Schizophrenia Research, 53, 7-16. Horn, J. L. (1985). Remodeling old models of intelligence. In B. Wolman (Ed.), Handbook of Intelligence (pp. 267- 300). New York: Wiley. Ilonen, T., Taiminen, T., Lauerma, H., Karlsson, H., Helenius, H., Tuimala, P., Leinonen, K., Wallenius, E., & Salokangas, R. (2000). Impaired Wisconsin Card Sorting Test performance in first episode schizophrenia: Resource or motivation deficit? Comprehensive Psychiatry, 41, 385- 391. Jackson, C., Fein, D., Essock, S., & Mueser, K. (2001). The effects of cognitive impairment and substance abuse on psychiatric hospitalizations. Community Mental Health Journal 37, 303-312. Johnson-Selfridge, M., & Zalewski, C. (2001). Moderator variables of executive functioning in schizophrenia: Meta- analytic findings. Schizophrenia Bulletin, 27, 305-316. Kaufman, A. S., & Lichtenberger, E. O. (2002). Assessing Adolescent and Adult Intelligence. Boston: Allyn & Ba- con. Kenny, J. T., & Meltzer, H. Y. (1991). Attention and higher cortical functions in schizophrenia. The Journal of Neuro- psychiatry and Clinical Neurosciences, 3, 269-275. King, M., & Snow, W. (1981). Problem-solving task per- formance in brain-damaged subjects. Journal of Clinical Psychology, 37, 400-404. Koren, D., Seidman, L., Harrison, R., Lyons, M., Kremen, W., Caplan, B., Goldstein, J., Faraone, S., & Tsuang, M. (1998). Factor structure of the Wisconsin Card Sorting Test: Dimensions of deficit in schizophrenia. Neuropsy- chology, 12, 289-302. Koren, D., Seidman, L., Poyurovsky, M., Goldsmith, M., Viksman, P., Zichel, S., & Klein, E. (2004). The neuro- psychological basis of insight in first-episode schizophre- nia: A pilot metacognitive study. Schizophrenia Research, 70, 195-202. Kremen, W., Seidman, L., Faraone, S., & Tsuang, M. (2001). Intelligence quotient and neuropsychological pro- files in patients with schizophrenia and in normal volun- teers. Society of Biological Psychiatry, 50, 453-462. Laws, K. (1999). A meta-analytic review of Wisconsin Card Sort studies in schizophrenia: General intellectual deficit in disguise? Cognitive Neuropsychiatry, 4, 1-35. Leong, F. (1989). Cultural variations in the treated preva- lence rate and symptomatology among Chinese, Japanese, Filipino, and Caucasian schizophrenic patients in Hawaii. In S. C. Schultz & C. Tamiga (Eds.), Schizophrenia: Sci- entific Progress (pp. 36-44). New York, New York: Ox- ford University Press. Lezak, M. D. (1995). Neuropsychological Assessment (3 rd ed.). New York: Oxford University Press. Liraud, F., & Verdoux, H. (2002). Effect of comorbid sub- stance use on neuropsychological performance in subjects with psychotic or mood disorders. Encephale, 28, 160- 168. Lopez-Luengo, B., & Vazquez, C. (2003). Effects of atten- tion process training on cognitive functioning of schizo- phrenic patients. Psychiatry Research, 119, 41-53. Lynn, R. (1996). Racial and ethnic differences in intelli- gence in the United States on the Differential Ability Scale. Personality and Individual Differences, 20, 271- 273. Metz, J. T., Johnson, M. D., Pliskin, N. H., & Luchins, D. J. (1994). Maintenance of training effects on the Wisconsin Card Sorting Test by patients with schizophrenia or affec- tive disorders. American Journal of Psychiatry, 151, 120- 122. Mirsky, A., Yardley, S., Jones, B., Walsh, D., & Kendler, K. (1995). Analysis of the attention deficit in schizophrenia: A study of patients and their relatives in Ireland. Journal of Psychiatric Research, 29, 23-42. Morice, R. (1990). Cognitive inflexibility and pre-frontal dysfunction in schizophrenia and mania. British Journal of Psychiatry, 157, 50-54. Morice, R., & Delahunty, A. (1996). Frontal/executive im- pairments in schizophrenia. Schizophrenia Bulletin, 22, 125-137. Mueser, K., Bellack, A., & Blanchard, J. (1992). Comorbid- ity of schizophrenia and substance abuse: Implications for treatment. Journal of Consulting and Clinical Psychology, 60, 845-856. Murray, R. (1994). Neurodevelopmental schizophrenia: The rediscovery of dementia praecox. British Journal of Psy- chiatry, 25, 6-12. Mussgay, L., & Hertwig, R. (1990). Signal detection indices in schizophrenics on a visual, auditory, and bimodal Con- tinuous Performance Test. Schizophrenia Research, 3, 303-310. Nuechterlein, K., Buchsbaum, M., & Dawson, M. (1994). Neuropsychological vulnerability to schizophrenia. In A. David & J. Cutting (Eds.), The Neuropsychology of Schizophrenia (pp. 53-73). Hove, U.K.: Lawrence Erl- baum Associates. Perrine, K. (1993). Differential aspects of conceptual proc- essing in the Category Test and Wisconsin Card Sorting EXECUTIVE FUNCTIONING IN SCHIZOPHRENIA 45 Test. Journal of Clinical and Experimental Neuropsychol- ogy, 15, 461-473. Perry, W., Potterat, E. G., & Braff, D. L. (2001). Self- monitoring enhances Wisconsin Card Sorting Test per- formance in patients with schizophrenia: Performance is improved by simply asking patients to verbalize their sorting strategy. Journal of the International Neuropsy- chological Society, 7, 344-352. Reed, R. A., Harrow, M., Herbener, E. S., & Martin, E. M. (2002). Executive function in schizophrenia: Is it linked to psychosis and poor life functioning? The Journal of Nerv- ous and Mental Disease, 190, 725-732. Regier, D., Farmer, M., Rae, D., Locke, B., Keith, S., Judd, L., & Goodwin, F. (1990). Comorbidity of mental disor- ders with alcohol and other drug abuse. Journal of the American Medical Association, 264, 2511-2518. Rund, B. R. (1998). A review of longitudinal studies of cognitive functions in schizophrenia patients. Schizophre- nia Bulletin, 24, 425-435. Saccuzzo, D., & Braff, D. (1981). Early information proc- essing deficit in schizophrenia. Archives of General Psy- chiatry, 38, 175-179. Seidman, L., Pepple, J., Faraone, S., Kremen, W., Cassens, G., McCarley, R., & Tsuang, M. (1991). Wisconsin Card Sorting Test performance over time in schizophrenia. Preliminary evidence from clinical follow-up and neuro- leptic reduction studies. Schizophrenia Research, 5, 233- 242. Sergi, M., Kern, R., Mintz, J., & Green, M. (2005). Learning potential and the prediction of work skill acquisition in schizophrenia. Schizophrenia Bulletin, 31, 67-72. Spreen, O., & Strauss, E. (Eds.). (1998) A Compendium of Neuropsychological Tests: Administration, Norms, and Commentary (2 nd ed., pp. 219-231). New York: Oxford University Press. Staats, A. W. (1989). Paradigmatic behaviorism’s theory of intelligence: A third generation approach to cognition. Psicothema, 1, 7-24. Staats, A. W. (1990). Paradigmatic behaviorism and intelli- gence: Task analysis? Technical plan? Or theory? Psi- cothema, 2, 7-24. Staats, A. W., & Burns, G. L. (1981). Intelligence and child development: What intelligence is and how it is learned and functions. Genetic Psychology Monographs, 104, 237-301. Stone, M., Gabrieli, J., Stebbins, G. T., & Sullivan, E. V. (1998). Working and strategic memory deficits in schizo- phrenia. Neuropsychology, 12, 278-288. Stratta, P., Daneluzzo, E., Prosperini, P., Bustini, M., Mattei, P., & Rossi, A. (1997). Is Wisconsin Card Sorting Test performance related to 'working memory' capacity? Schizophrenia Research, 27, 11-19. Stratta, P., Mancini, F., Mattei, P., Casacchia, M., & Rossi, A. (1994). Information processing strategy to remediate Wisconsin Card Sorting Test performance in schizophre- nia: A pilot study. American Journal of Psychiatry, 151, 915-918. Stuss, D., & Benson, D. (1986). The Frontal Lobes. New York, NY: Raven Press. Sue, S. (1999). Science, ethnicity, and bias: Where have we gone wrong? American Psychologist, 54, 1070-1077. Suzuki, L., & Valencia, R. (1997). Race-ethnicity and meas- ured intelligence: Educational implications. American Psychologist, 52, 1103-1114. Sweeney, J., Kelip, J., Haas, G., Hill, J., & Weiden, P. (1991). Relationships between medication treatments and neuropsychological test performance in schizophrenia. Psychiatry Research, 37, 297-308. Tukey, J. (1977). Exploratory Data Analysis. Reading, MA: Addison-Wesley. Vollema, M. G., Geurtsen, G. J., & van Voorst, A. (1995). Durable improvements in Wisconsin Card Sorting Test performance in schizophrenic patients. Schizophrenia Re- search, 16, 209-215. Wechsler, D. (1997). WAIS-III administration and scoring manual. San Antonio, TX: Psychological Corporation. Weickert, T. W., Goldberg, T. E., Gold, J. M., Bigelow, L. B., Egan, M. F., & Weinberger, D. R. (2000). Cognitive impairments in patients with schizophrenia displaying preserved and compromised intellect. Archives of General Psychiatry, 57, 907-913. Woonings, F., Appelo, M. T., Kluiter, H., Slooff, C. J., & van den Bosch, R. J. (2002). Learning (potential) and so- cial functioning in schizophrenia. Schizophrenia Re- search, 59, 287-296. Young, D. A., & Freyslinger, M. G. (1995). Scaffolded instruction and the remediation of Wisconsin Card Sorting Test deficits in chronic schizophrenia. Schizophrenia Re- search, 16, 199-207.