Psychiarty Research 149, 25-31 (2007)

Clear distinction between preattentive and attentive processes in schizophrenia by visual search performance

Goro Tanaka, Shuji Mori,Hiroyuki Inadomi, Yoshito Hamada, Yasuyuki Ohta, Hiroki Ozawa

Visual information processing deficits were investigated in patients with schizophrenia using visual search tasks. Subjects comprised 20 patients with schizophrenia and 20 normal subjects. Visual search tasks were modified from those used previously to reveal more distinct differences between feature and conjunction search tasks. The presentation area of items in the present study was more than double the area used in our previous study (Mori et al., 1996), and items were distributed over the area randomly in each trial to produce a certain range of locational jitter for each item across trials that prevented a matrix-like presentation of items at fixed positions (Mori et al., 1996). The target was a red square, and distractors were red circles in the feature search task and red circles and green squares in the conjunction search task. Slopes and intercepts of a linear function relating reaction times to set size were computed. In the feature search task, slopes for both groups were almost zero. In the conjunction search task, significant differences in slopes were seen between the two groups irrespective of target presence or absence. Moreover, the slopes were approximately twice as steep during target absence as during target presence. These results indicate more definitively than the results of our previous study (Mori et al., 1996) that patients with schizophrenia have deficits in focal attentional processing although their preattentive processing functions at a normal level.