11. Psychology, Neuro- 145 severity, substance misuse, dose or chronicity of medication or ver- bal/performance differences. In conclusion, IQ decline is associated with a reduction in total white matter and possibly an increase in CSF volume in our sample of schizophrenia patients. Further analy- ses will attempt to identify the anatomical location of these volume changes. A PROCESS APPROACH TO VERBAL FLUENCY TASKS IN PATIENTS WITH SCHIZOPHRENIA L. M. Maron,* M. Carlson, A. Minassian, W. Perry Neuropsychiatry and Behavioral Medicine, University of California San Diego, San Diego, CA, USA Verbal fluency is a critical measure of cognitive functioning that is dependent upon multiple cognitive processes including sensory pro- cessing of the cue, successful retrieval, integrity/organization of the semantic store and overt articulation of the response. On tests of ver- bal fluency, schizophrenia patients tend to produce fewer words over- all, in addition to frequent perseverations and intrusions relative to healthy comparison subjects (Allen et al., 1993). Although there is a relatively large body of research documenting this phenomenon, there is little agreement upon the underlying mechanism of impair- ment. One hypothesis involves disruption in frontal-lobe mediated initiation and search strategies, which reduces access to semantic memory (Joyce et al., 1996). A competing hypothesis suggests dis- organization or reduction of the semantic store, implicating the tem- poral-lobe structures upon which semantic processing is at least par- tially dependent (Paulsen et al., 1996). To address this controversy, the present study examined category and letter fluency performance in a group of 20 well-diagnosed schizophrenia patients and a healthy age and sex matched comparison group using a neuropsychological "process" approach, which has characterized linguistic errors on oth- er tests (Kaplan, 1978). This approach enabled us to assess the num- ber and length of word clusters as well as the total number and appro- priateness of responses generated. Consistent with previous research, schizophrenia patients demonstrated impaired performance across both verbal fluency tasks, with a relatively greater impairment on letter fluency. Process analyses revealed that in the schizophrenia group, performance on the letter fluency task was characterized by a decreased amonnt of clustering (t(1,33) = -2.8; p = .008). No signi- ficant differences in cluster size were found. Further, negative symp- toms were inversely correlated with performance on both fluency tasks, in addition to the number of clusters produced (r = -.63; p = .003). Collectively, these results suggest that a breakdown in the executive control of linguistic behvavior may undelie impaired ver- bal fluency in schizophrenia, and provide insight into the neu- ropathology of the disease. POSTURAL STABILITY IN SCHIZOPHRENIA C. L. Marvel,* B. L. Schwartz, R. B. Rosse Mental Health Service Line, VAMC, Washington, DC, USA There is growing interest in cerebellar dysfunction in schizophrenia. It has been suggested that disrupted cerebellar circuitry can lead to reduced coordination of thought, or "cognitive dysmetria." This con- cept is analogous to the motor incoordination that arises from cere- bellar dysfunction. The cerebellum serves a primary role in the con- trol of muscle groups involved in stationary posture and balance. In fact, unsteady postural stance, or sway, has been quantified in patients with cerebellar abnormalities for several decades. Given the numer- ous reports of structural abnormalities of the cerebellum in schizo- phrenia, surprisingly few studies have quantified postural sway asso- ciated with this disorder. This study compared 24 schizophrenia patients with 24 non-psychiatric controls on a quantitative measure of postural sway that frequently has been used to examine cerebel- lar abnormalities. Postural stability was tested by asking participants to stand on a platform that recorded shifts in weight through pressure points in the feet. Postural sway was determined by displacement of pressure from a center point on the platform. Participants were instructed to stand in ten different positions throughout the test ses- sion. Each position challenged postural stability by reducing visual and/or proprioceptive input (e.g., standing with eyes closed, feet close together, and arms raised). Patients demonstrated more pos- tural sway compared with healthy controls (p < .001). Postural sway was not related to tardive dyskinesia, which was assessed by the Abnormal Involuntary Movement Scale (AIMS). When 9 patients with an AIMS score above a 0 (i.e., those patients who showed even minimal signs of abnormal movements) were removed from analy- ses, group differences remained (p < .01). There was no significant correlation between neuroleptic medication level and degree of pos- tural sway (r =.20, p =.36). These results indicate that patients with schizophrenia have fundamental disturbances in the control of pos- ture and balance. Because the cerebellum is a key structure in a neu- ral system that underlies postural stability, deficits shown here sug- gest that these patients may have a disrupted cerebellar circuit. Moreover, precise quantitative recording of postural sway may be a more sensitive means of detecting disturbances of movement than are standard clinical observations (e.g., the AlMS assessment). Fund- ing by: NIMH F31MH12207 & NARSAD PERCEPTUAL AND WORKING MEMORY IMPAIRMENTS IN FIRST-EPISODE AND CHRONIC SCHIZOPHRENIA B. Mathes,* S. J. Wood, T. M. Proffitt, J. A. Buchanan, W. J. Brewer, R D. McGorry, C. Pantelis Cognitive Neuropsychiatry Research and Academic Unit, The University of Melbourne and Sunshine Hospital, Melbourne, VIC; Australia It has been argued that working memory (WM) deficits in schizo- phrenia are exacerbated by other impairments, e.g. by those affect- ing visual processing. The delayed match to sample (DMTS) para- digm from the Cambridge Neuropsychological Test Automated Battery is especially suitable to investigate the contribution of per- ceptual and memory processes involved in object WM deficits, as it contains immediate and delayed recognition trials (0, 4 and 12 sec- onds) as well as a simultaneous matching (SM) control condition. We investigated 55 patients in their first-episode of a schizophreni~ form disorder (FE), 50 patients with chronic schizophrenia (SZ) and 56 gender-matched healthy controls (CTL). An initial assessment of the DMTS error data revealed a skewed distribution, which was sub- sequently modelled using negative binominal regression, covarying for age and premorbid IQ. For the total error score of all task condi- tions this model revealed a highly significant effect of group (P<0.01) and condition (P< 0.0001). The comparison between groups using their total error score revealed that both FE patients (P<0.01) and SZ patients (P<0.0 t) performed worse than the CTL. To investigate the impact of perceptual matching to delay dependent WM processes, the SM error score was incorporated into the model as a covariate, analysing only the 0 sec, 4 sec and 12 sec trials. The significant effect of group (P<0.05) and condition (P< 0.0001) remained, while the post-hoc analyses showed that only the FE-paticnts (P<0.05) per- formed significantly worse than the CTL, with the SZ group show- ing a trend for impairment (P=0.072). These results suggest that both International Congress on Schizophrenia Research 2003