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Schizophrenia Research xxx (2010) xxx–xxx

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Contents lists available at ScienceDirect

Schizophrenia Research

j ourna l homepage: www.e lsev ie r.com/ locate /schres

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Has an important test been overlooked? Closure flexibility in schizophrenia

Pamela D. Butler a,b,c,⁎, Isaac Schechter d, Nadine Revheim a, Gail Silipo a, Daniel C. Javitt a,b,c

a Schizophrenia Research Center, Nathan Kline Institute for Psychiatric Research, Orangeburg, NY 10962, United Statesb Department of Psychiatry, New York University School of Medicine, New York, NY 10016, United Statesc City College of the City University of New York, New York, NY 10031, United Statesd Bikur Cholim, Monsey, NY, United States

a r t i c l e i n f o

UN⁎ Corresponding author. Nathan Kline Institute for140 Old Orangeburg Rd, Orangeburg NY, 10962, Unite398 6537; fax: +1 845 398 6545.

E-mail address: butler@nki.rfmh.org (P.D. Butler).

0920-9964/$ – see front matter © 2010 Published bydoi:10.1016/j.schres.2010.01.005

Please cite this article as: Butler, P.D., etSchizophr. Res. (2010), doi:10.1016/j.schr

a b s t r a c t

O

Article history:Received 18 October 2009Received in revised form 7 January 2010Accepted 11 January 2010Available online xxxx

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ODeficits in visual processing are now recognized as a core feature of schizophrenia. In the 1940s,Louis Thurstone developed a series of tests designed to evaluate specific aspects of visualperceptual processing including the Closure Flexibility Test (CFT),whichwas designed tomeasure“the ability to hold a configuration in mind despite distraction.” The present study evaluatedpatients' performance on this task and its relationship to other tests of neuropsychologicalfunction, particularly to a measure of sustained visual attention. Thirty-nine patients withschizophrenia or schizoaffective disorder and 40 controls participated. The CFT was administeredboth in its original form (10 min) and also in a briefer form (3 min) in which only a portion ofstimuliwere given. Patients showedhighly significant large effect-size deficits onboth the original(d=1.6) and brief (d=1.2) CFT. Between-group deficits in performance survived co-variation forIQ. In addition, the CFT scorewas significantly related to performance on theMATRICSmeasure ofattention/vigilance, the Continuous Performance Test—Identical Pairs version (CPT-IP). Thiscorrelation remained significant even after controlling for non-specific intercorrelations amongneurocognitive measures. Results confirm the severity of early visual processing deficits inschizophrenia. In addition, the CFT is a brief, easy to administer alphabet-independent, paper-and-pencil test with established psychometric properties that may be useful as an index of thesustained visual attention construct in schizophrenia.

© 2010 Published by Elsevier B.V.

Keywords:SchizophreniaAttentionPerceptionClosure Flexibility TestContinuous Performance TestNeuropsychological tests

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1. Introduction

Schizophrenia is a complex disorder associated with in-formation processing deficits across a range of cognitivedomains. Deficits in visual processing manifest as reducedability to maintain sustained visual attention (Cornblatt et al.,1988), as well as reduced ability to decode complex informa-tion (Crookes, 1984; Kurachi et al., 1994). In the consensusMeasurement and Treatment Research to Improve Cognitionin Schizophrenia (MATRICS) test battery (Nuechterlein andGreen, 2006) sustained visual attention is evaluated using theIdentical Pairs Continuous Performance Test (CPT-IP). Other

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al., Has an importantes.2010.01.005

tests sensitive to visual dysfunction in schizophrenia includethe Perceptual Organization Index (POI) and the ProcessingSpeed Index (PSI) of the Wechsler Adult Intelligence Scale-III(WAIS;Wechsler, 1997a) which are known to be abnormal inschizophrenia (Dickinson et al., 2004).

Although most tests of visual processing assess relativelyhigh-order aspects of visual dysfunction, recent studiessuggest that patients show deficits even in relatively simpleprocesses (Butler et al., 2008, for review; Chen et al., 2005;Keri et al., 2004). The degree to which the various measuresinterrelate, as well as the identification of paper-and-pencilinstruments sensitive to various levels of visual dysfunctionin schizophrenia, remain areas of active investigation.

The present study evaluates the sensitivity of the ClosureFlexibility-Concealed Figures Task (CFT; Thurstone andJeffrey, 1984a,b) to cognitive dysfunction in schizophreniaand, in particular, to the construct of sustained visual

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attention. In his pioneering factor analytic study in the 1940s,Thurstone examined sixty perceptual measures, includingGottschaldt Figures which were an early form of the CFT. Heidentified 11 factors, seven of which were interpretable(Holzman, 1972; Thurstone, 1944) and named them: A)ability to hold a configuration in mind despite distractionincluding strength of configuration; B) proneness to classicalillusions; C) reaction time; D) speed of alternation of gaze; E)“freedom from Gestaltbindung” involving flexibility in ma-nipulating several more or less irrelevant or conflictinggestalts; F) speed of perception; and J) speed of judgement.The Gottschaldt figures, along with other tests, loaded sig-nificantly on factors A and E. These two factors have sharedvariance, as seen by the correlation of 0.38 that Thurstone(1944) found between them. Thurstone (1951) later foundthat the Gottschaldt Figures loaded significantly only on hissecond closure factor which he defined as “ability to hold aconfiguration in mind despite distraction.”

In the present version of the CFT, participants are shown aseries of relatively simple, reference figures and required tostate whether or not these figures are embedded within morecomplex test pictures. Although the test is timed (10 min)scoring is performed based only upon whether evaluationsare correct or incorrect for the items completed. Bothreference and probe stimuli remain visible throughout thetest, so correct performance requires primarily comparisonand contrast of images to evaluate simple shapes embeddedwithin more complex figures. The task format prevents bothimages from being centered in the field of view simulta-neously, so the experience of the task is of needing to hold thetarget shape in mind, even while ignoring the extraneousvisual information in the more complex figure, as originallyproposed by Thurstone (1944). However, this should not beconfused with the construct of “holding and manipulatingmental information” subsequently proposed by Baddeley(1992) and others to refer to “central executive” type workingmemory systems.

Scaled scores for the CFT can be calculated based uponresults from normative samples, and used for between-groupcomparisons. The CFT has been shown to have strongpsychometric properties as seen in split-half reliability of0.78 and 0.94 in two studies (Pemberton, 1951; Thurstone,1944). To date, however, test–retest reliability and potentiallearning effects have not been evaluated, nor are alternateforms available.

While the CFT is a paper-and-pencil task with simulta-neous display of information, more recent tests of visualattention have tended to use sequential display within theContinuous Performance Task (CPT) format. There are anumber of versions of this task including the degraded CPT,the CPT-IP, and the AX-CPT (Cornblatt et al., 1988; Delawallaet al., 2008; Javitt et al., 2007; Rissling et al., 2005). The CPT iswidely used in schizophrenia research and is currentlyconsidered the “gold standard” measure of visual attention.The CPT-IP was chosen for use in the MATRICS battery(Nuechterlein and Green, 2006).

For the present study, CFT performance was evaluated inschizophrenia patients relative to controls. Further, withinpatients, CFT performance was evaluated relative to neuro-psychological tests sensitive to discrete cognitive domainsincluding CPT-IP. In addition, a brief 3-minute version of the

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CFT was administered. The goal of this study was to comparethe visual attention construct developed by Thurstone (1944)and subsequently adopted by other early-stage visualresearchers in schizophrenia (e.g. Holzman, 1972) to theconstruct as currently implemented. In addition, the studyevaluates the sensitivity of the CFT to neurocognitivedysfunction in schizophrenia and provides initial assessmentof applicability in this population.

2. Experimental methods

2.1. Participants

This study was approved by the Nathan Kline Institute IRB.All participants provided written informed consent followingfull explanation of experimental procedures. Patients wererecruited from outpatient and inpatient units. Diagnoseswere obtained using the Structured Clinical Interview forDSM-IV (SCID; First et al., 1997) and available clinicalinformation. Controls with a history of SCID-defined Axis Ipsychiatric disorder were excluded. Participants were ex-cluded if they had any neurological or ophthalmologicdisorders that might affect performance or met criteria foralcohol or substance dependence within the last six monthsor abuse within the last month. All participants had at least20/32 corrected visual acuity on the Logarithmic Visual AcuityChart (Precision Vision, LaSalle, IL).

Participants who received the Standard Version of the CFTincluded 18 patients meeting DSM-IV criteria for schizophre-nia or schizoaffective disorder and 23 comparison subjects(Table 1). Patients did not differ in age (t(39)=0.8, p=0.4),gender ratio (Fisher's exact test; p=1.0) or parentalsocioeconomic status (t(33)=1.1, p=0.3), but did differ inIQ (t(30)=3.1, p=0.004). All patients were taking atypicalantipsychotic medication at the time of testing. Chlorprom-azine (CPZ) equivalents were calculated using conversionfactors described previously (Hyman et al., 1995; Jibson andTandon, 1998; Peuskens and Link, 1997; Woods, 2003).

Participants who received the Brief Version of the CFTincluded 21 patients meeting criteria for schizophrenia orschizoaffective disorder and 17 comparison subjects (Table 1).Separate groups of participants received the brief and StandardCFTs. Patients and controls were of similar age (t(36)=0.1,p=0.9) and did not differ on gender ratio (Fisher's exact test;p=0.6) or parental socioeconomic status (t(28)=0.5,p=0.6), but did differ on IQ (t(33)=4.0, p<0.001).

2.2. CFT

2.2.1. Standard CFTThe Standard CFT (Thurstone and Jeffrey, 1984a) was

administered according to published guidelines. The CFT is a49-item test that displays a figure on the left that isembedded within several of the 4 complex drawings thatare displayed to its right. Participants are given 10 min to doas much as they can and are asked to put a check mark underthe complex drawings that contain the figure and a “0” underdrawings that do not. A scaled score is derived from totalcorrect minus total incorrect responses (Thurstone andJeffrey, 1984a,b) Percent correct, false positives, and falsenegatives can also be calculated.

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Table 1t1:1

Demographic and clinical characteristics.t1:2

t1:3 Standard CFT Controls(n=23)

Patients(n=18)

t1:4 Age 36.5±11.5 38.9±7.2t1:5 Gender (M/F) 12/11 10/8t1:6 Parental socioeconomic status 50.1±10.3

(n=23)43.3±19.7(n=12)

t1:7 Quick Test IQ 110.6±10.3(n=17)

98.7±11.6*(n=15)

t1:8 Schizophrenia/schizoaffectivedisorder

14/4

t1:9 Chlorpromazine dailyequivalent, mg

1192.4±552.8

t1:10 BPRS total score 34.5±10.1(n=15)

t1:11 SANS total score (includingglobal scores)

32.7±17.2(n=15)

t1:12

t1:13 Brief CFT Controls(n=17)

Patients(n=21)

t1:14 Age 34.6±9.9 34.9±8.4t1:15 Gender (M/F) 15/2 20/1t1:16 Parental socioeconomic status 41.8±12.6

(n=17)39.6 ±13.4(n=13)

t1:17 Quick Test IQ 109.1 ± 7.0(n=16)

98.7±8.1 ⁎

(n=19)t1:18 Schizophrenia/schizoaffective

disorder18/3

t1:19 Chlorpromazine dailyequivalent, mg

1086.7±522.4

t1:20 BPRS total score 45.4±12.5t1:21 SANS total score (including

global scores)44.7±13.5

Values are mean±SD. Numbers of subjects per group are noted when thereis missing data. Socioeconomic status was measured by the 4-factorHollingshead Scale (Hollingshead, 1975). IQ was measured using the QuickTest (Ammons and Ammons, 1962). Abbreviations: CFT, Closure FlexibilityTest; M, male; F, Female; BPRS, Brief Psychiatric Rating Scale (Overall andGorham, 1962); SANS, Schedule for Assessment of Negative Symptoms(Andreasen, 1984).

t1:22 ⁎ p<0.05.t1:23

able 2 t2:1

ean (SD) Closure Flexibility Test (CFT) performance in controls (n=23)nd patients (n=18) for standard administration.

t2:2

t2:3Measure Controls Patients T p d

t2:4Total items completed 96.3 (22.9) 117.6 (44) 1.9 0.07 0.7t2:5# Correct responses 80.5 (23.2) 70.3 (21.4) 1.4 0.16 0.5t2:6Percent correct 83.1 (10.9) 62.8 (14.5) 5.1 <0.001 1.6t2:7# Incorrect responses 15.8 (10.4) 47.3 (29.1) 4.4 <0.001 1.7t2:8# False negatives 12.3 (8.9) 31.1 (25.4) 3.0 0.007 1.2t2:9# False positives 3.5 (2.8) 16.3 (17.5) 3.1 0.007 1.4t2:10Correct–incorrect 64.7 (27.7) 22.9 (25.9) 4.9 <0.001 1.6t2:11Scaled scores 50.3 (9.8) 34.6 (10.2) 5.0 <0.001 1.6

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2.2.2. Brief CFTThe first 14 items of the Standard CFT were administered.

Participants were given 3 min to complete the task. Scoring,including percent correct, was the same as for the StandardCFT, except that scaled scores were not available for this briefadministration.

2.3. Other neuropsychological tests

Neuropsychological measures were administered topatients who agreed to participate in additional testing asfollows: 1) The CPT-IP is a computer-generated and timedmeasure assessing attentional capacity with increased loadduring continuous performance on trials of 2, 3 and 4 digits(Cornblatt et al., 1988). CPT-d′ is derived from hits and falsealarms and was the variable used in this study; 2) The PSI is afactor score derived from scaled scores for performance onthe Digit Symbol and Symbol Search subtests of the WAIS-III(Wechsler, 1997a) and reflects speed of processing; 3) ThePOI is a factor score derived from scaled scores forperformance on the Picture Completion, Block Design, andMatrix Reasoning subtests of the WAIS-III (Wechsler, 1997a)and reflects perceptual organization; 4) The WMI is a factor

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score derived from scaled scores for performance on LetterNumber Sequencing and Spatial Span subtests of the WMS-III(Wechsler, 1997b) and reflects verbal and visual workingmemory; 5) The BVMT-R is a standardized visual learning andmemory task (Benedict et al., 2007). The raw score for thesum of all immediate recall trials (1–3) was the variable used;6) The WMS-III Logical Memory Test (LM) involves narrativerecall of verbal material read aloud (Wechsler, 1997b). Thescaled score for total recall on the LM subtest was the variableused; 7) The Quick Test IQ measure is based on the selectionof an appropriate visual scene that depicts increasinglydifficult vocabulary cues (Ammons and Ammons, 1962).Scaled score is based on total correct items andwas the variableused.

2.4. Statistical analysis

Between-group comparisons were performed by Studentt-test or analysis of variance (ANOVA) as appropriate.Secondary analyses were carried out using IQ as a covariate.Relationships among CPT-IP and CFT were assessed usingPearson product-moment correlations followed by step-wiseregression to determine whether the CFT contributes to asignificant amount of the variance in CPT-IP performanceafter other factors are taken into account. Effect sizes forpatients and controls were computed using the standarddeviations from patient and control groups, respectively.Neuropsychological test scores, with the exception of theQuick IQ test, were only available for the group who receivedthe Standard CFT and only patients received neuropsycho-logical testing.

3. Results

3.1. Standard CFT

3.1.1. Between-group effectsPatients showed significant, large effect-size deficits

compared with controls on CFT performance, consistentwith the a priori hypothesis (Table 2). Patients showedsignificant deficits in percent correct, with differences drivenlargely by the number of incorrect rather than correctresponses. Patients' impaired performance was not due to alack of task engagement as they completed as many or moreitems than controls. However, many more of their responseswere incorrect, which included false positives and falsenegatives. Patients and controls showed similar patterns offalse negatives and false positives as seen by a non-significant

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Table 4 t4:1

Mean (SD) Closure Flexibility Test (CFT) performance in controls (n=17)and patients (n=21) for short administration.

t4:2

t4:3Measure Controls Patients T p d

t4:4Total items completed 32.1 (9.7) 28.8 (11.5) 0.9 0.4 0.3t4:5# Correct responses 27.1 (9.4) 20.4 (9.4) 2.2 0.04 0.7t4:6Percent correct 84.0 (11.5) 69.9 (11.9) 3.7 0.001 1.2t4:7# Incorrect responses 5.0 (3.7) 8.4 (4.5) 2.5 0.02 0.8t4:8# False negatives 4.1 (3.4) 6.3 (3.5) 1.9 0.06 0.6t4:9# False positives 0.9 (0.9) 2.1 (2.4) 2.2 0.04 0.7t4:10Correct–incorrect 22.1 (10.6) 11.9 (9.3) 3.1 0.003 1.0

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Group×Error type interaction (F(1,39)=0.7, p=0.41). Thissuggests that patients were able to perform the taskwithout aresponse bias for respondingwith all false positives or all falsenegatives. The magnitude of the deficits for both the scaledscore and percent correct were 1.6 SD units, which is largeaccording to the criteria of Cohen (1988).

In a secondary analysis using ANCOVA with percentcorrect performance on the CFT as the dependent measure,between-group factor of cohort, and IQ as covariate, the maineffect of cohort remained strongly significant (F1,29=10.0,p=0.004). The effect of IQ as covariate was also nearlysignificant (F1,29=3.09, p=0.09) but obviously did notaccount for most of the between-group variance.

3.1.2. Within-patients effectsIn order to identify the relationship between CFT deficits

and sustained visual attention, a correlation was performedfollowed by multi-step regression analyses (Table 3). Onlypatients were included in this analysis (n=14 participated inneuropsychological testing). There was a significant correla-tion between percent correct on the CFT and d′ on the CPT-IP(r=0.67, p=0.009; Table 3). In separate regression analyses,neuropsychological tests variables PSI, POI, WMI, BVMT-R, orLM were loaded into the regression vs. d′ CPT-IP performancein block 1, and then CFT (percent correct) was added in block2. Table 3 shows that the CFT accounted for a significantcomponent of the variance in the CPT-IP, even after PSI, POI,WMI, BVMT-R or LM were entered into the regression. Incontrast, when CFT was entered first, PSI did not account foran additional significant percentage of variance in CPTperformance. This supports a preferential relationship be-tween CFT and CPT-IP.

3.2. Brief CFT

On the Brief CFT, patients also showed significant deficitscompared to controls (Table 4). Patients had fewer correctresponses than controls and, as in the Standard CFT, showed

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Table 3Correlation between Closure Flexibility Task (CFT) performance andContinuous Performance Task—Identical Pairs (CPT-IP) prior to andfollowing control for specific cognitive task performance in patients.

First step Second step R change F change Sig (p)

None CFT 0.67 9.5 0.009PSI CFT 0.56 6.3 0.029POI CFT 0.74 16.0 0.002WMI CFT 0.74 13.8 0.003BVMT-R CFT 0.65 8.8 0.013LM CFT 0.68 8.5 0.015None PSI 0.35 1.7 0.216CFT PSI 0.00 0.01 0.926

Analyses were performed using step-wise regression, with indicatedvariables forced into the regression in the first and second steps andIdentical Pairs Continuous Performance Task (CPT-IP) as the dependenvariable. CFT vs. CPT-IP correlations remained significant even followingcorrection for non-specific inter-correlation among neuropsychologicameasures using Processing Speed Index (PSI), Perceptual OrganizationIndex (POI), Working Memory Index (WMI), Brief Visuospatial MemoryTest—Revised (BVMT-R), and the Logical Memory Test (LM). Note that Rchange is the square root of R2 change. In the instance when CFT is enteredalone vs. CPT-IP, with no previous variable entered, R change is thecorrelation between CFT and CPT-IP.

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significantly increased incorrect responses. Also like theStandard CFT, patients and controls showed similar patternsof false negatives and false positives as seen by a non-significant Group×Error type interaction (F(1,36)=0.6,p=0.5). While the brief version is not standardized, as inthe standard version the deficit in percent correct (1.2 SDunits) was large. Neuropsychological data were not availablefor this sample.

In a secondary analysis using ANCOVA with percentcorrect performance on the CFT as the dependent measure,between-group factor of cohort, and Quick Test IQ ascovariate, the main effect of cohort remained stronglysignificant (F1,32=5.25, p=0.03). The effect of IQ as acovariate was not significant (F1,32=1.74, p=0.2).

3.3. Medication effects and symptom ratings

There were no significant correlations between medica-tion dose and percent correct on the Standard CFT (r=−0.16, p=0.5) or the Brief CFT (r=−0.4, p=0.07).

There were no significant correlations between BriefPsychiatric Rating Scale total score (BPRS) or the Schedulefor Assessment of Negative Symptoms (SANS) total scoreincluding global scores and percent correct on the StandardCFT (BPRS: r=−0.46, p=0.08; SANS: r=0.002, p=0.9) orBrief CFT (BPRS: r=−0.37, p=0.1; SANS: r=0.05, p=0.8).

4. Discussion

Cognitive dysfunction is a major current concern inschizophrenia and a primary target for therapeutic interven-tion. Recent consensus batteries propose multidimensionalassessments with anywhere from 6 to 12 domains (Kernet al., 2004). Although the majority of domains in neuropsy-chological assessment batteries can be assessed throughpaper-and-pencil tests, sustained visual attention is currentlyassessed primarily through the use of computerized testsrequiring specialized programs and equipment. Althoughsuch tests are considered ideal in specialized researchsettings, they may be difficult to implement in less estab-lished clinical environments. The CFT is a visual processingtask originally designed to assess visual attentional function-ing among normal individuals.

The primary findings of the present study are first, thatschizophrenia subjects show large effect-size deficits in CFTperformance, and, second, that performance on this taskexplains a significant amount of the variation in sustainedvisual attention assessed with the CPT-IP even after othervariables such as processing speed have been entered into the

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equation. The present findings thus raise the possibility thatthe CFT may serve as a proxy for the CPT-IP and takes lesstime to administer.

Scaled scores are based upon the difference betweencorrect and incorrect responses rather than total itemscompleted. Patients completed a similar number of items ascontrols in this pilot study, but made far more incorrectassessments. Incorrect assessments, moreover, included bothfalse positives in which patients incorrectly reported embed-ded figures were present when they were not, as well as falsenegatives, in which no response was made. Importantly,because there is potential for both omission and commissionerrors, total non-response or chance responding does notproduce extreme scores.

The CFT was originally developed to assess the “secondclosure factor” of Thurstone (1944, 1951), which he definedas “the ability to hold a configuration in mind despitedistraction.” As compared to the CPT-IP, reference and teststimuli are present simultaneously. However, because of thecomplexity of the figures, frequent cross-referencing betweenfigures is required, necessitating sequential processing.

As hypothesized, the CFT task was significantly related(r=0.67, p=0.009) to sustained visual attention assessedwith the CPT-IP, accounting for ∼45% of the variance.Furthermore, the relationship remained significant evenwhen non-specific correlations among neuropsychologicalmeasures were controlled for using step-wise regressionanalyses (Table 3). In particular, although the CFT is timed,controlling for general reductions in processing speed usingthe PSI did not eliminate the CFT vs. CPT-IP correlation.Similarly, the correlation remained significant even aftercontrolling for working memory using the WMI, suggestingthat the CFT and CPT-IP both measure a shared underlyingconstruct (i.e. visual attention).

Despite the venerability of the CFT task, this is thefirst studyof which we are aware to apply this test to schizophrenia.Although its psychometric properties in schizophrenia remainlargely unknown, the fact that it is well validated and stan-dardized in normative populations, shows large effect size(d>1.0) between-group differences, is easy to administer andwas well tolerated by our patients makes it worthy of furtherinvestigation. Interestingly, patientswith autismshowsuperiorperformance to controls on similar tasks (Dakin and Frith,2005), suggesting that deficits may be relatively selective toschizophrenia over other neuropsychiatric populations.

The standard version of the CFT task requires 10 min toadminister, which is shorter than the CPT-IP as presentlyimplemented, and does not require specialized equipment.The CFT is also language-, alphabet- and culture-independent,which maymake it useful for cross-national investigations. Inthis study, however, we also evaluated whether between-group differences could be obtained using a briefer versionincorporating only 14 of the 49 stimuli and 3 min of testingtime (similar to other MATRICS tasks). Significant between-group differences were obtained even with this brieferversion, suggesting the possibility that subtests and alternateforms of the test can be developed. A further beneficialpsychometric aspect of the CFT is that controls score between80 and 85% correct rather than at ceiling. Psychometric testsare most discriminating when the mean response of controlsis midway between chance and ceiling.

Please cite this article as: Butler, P.D., et al., Has an importantSchizophr. Res. (2010), doi:10.1016/j.schres.2010.01.005

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The CFT was specifically developed to test the visualattention construct, and results from the present papersupport its use in schizophrenia. Furthermore, at present,the CFT is used as part of a test battery for occupationalfunctioning (Thurstone and Jeffrey, 1984b). A major issue inschizophrenia is outcome and ability to engage in supportedemployment. Thus, studies looking at relationships betweenCFT performance and occupational functioning in schizo-phrenia may be useful.

In summary, ideal tests for assessment of visual dysfunc-tion in schizophrenia are still being developed. Results fromthe present study suggest that a classic test of sustained visualattention—Thurstones's CFT—is sensitive to psychopathologyin schizophrenia, and that impairments in visual attentionmay contribute to overall neurocognitive dysfunction.

Role of funding sourceFunding for this study was provided by USPHS grants RO1 MH66374

(PDB); R37 MH49334 and K02 MH01439 (DJC) and a Burroughs WellcomeTranslational Scientist Award (DJC). Neither Burroughs Wellcome nor theNIMH had any further role in study design; in the collection, analysis andinterpretation of data; in the writing of the report; and in the decision tosubmit the paper for publication.

ContributorsDrs. Butler, Schechter, Revheim, and Javitt designed the study, wrote the

protocol, managed the literature searches, and undertook the analyses. Ms.Silipo recruited participants. Dr. Schechter collected data. All authorscontributed to and approved the final manuscript.

Conflict of interestNone.

AcknowledgementsNone.

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