Original articleGlobal–Local Visual Processing in Schizophrenia: Evidence for an Early Visual Processing Deficit
Section snippets
Participants
The sample consisted of 24 stable outpatients (14 male) with schizophrenia. The comparison group was 29 healthy individuals (15 male) with no history of schizophrenia or affective illness in a first-degree relative. Average (SD) duration of illness was 7.71 (7.56) years. All but one patient was medicated, 17 with atypical and 6 with typical antipsychotics. All subjects underwent medical, neurological and psychiatric evaluations (Structured Clinical Interview for DSM-IV [SCID], Patient or
Performance Data
The analysis of RT (Table 1) revealed a significant condition (global vs. local) × diagnosis interaction (Figure 4). Specifically, in patients, median RT to global targets (mean [SD] = .694 [.127] sec) was delayed relative to local targets (.646 [.124] sec) [F(1,48) = 17.10, p < .001]; in control subjects, median RT was comparable across the two conditions (global: .644 [.115] sec; local: .640 [.105] sec) [F(1,48) = .10, p = .75]. This delayed global RT in patients also contributed to a
Discussion
The results of primary interest in this study reflect patient–control differences and the modulation of these group differences by stimulus condition. These results can be summarized as follows: 1) patients had slower and less accurate responses to global stimuli, with an accuracy impairment especially evident among female patients; 2) patients had decreased N150 amplitudes, with reverse hemispheric asymmetry (left > right) in response to local stimuli; and 3) patients had earlier P300
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