INFLUENCE OF PERCEPTUAL AND SEMANTIC CONFLICTS BETWEEN THE 2 HALVES OF CHIMERIC STIMULI ON THE EXPRESSION OF VISUOSPATIAL NEGLECT

We investigated how perceptual and semantic relationships between the left and right half of chimeric stimuli influence overt and covert vis ual processing by asking eight right brain damaged (RED) patients with hemispatial neglect to identify complete, half-, and chimeric drawing s. Chimeric stimuli belonged in one of four categories defined accordi ng to the perceptual and semantic relatedness between the two compound ing hemi-figures. Thus, the hemi-figures could be related both percept ually and semantically, only perceptually, only semantically, or neith er perceptually nor semantically. Although patients often appeared to base their report on the right part of the chimerics, the number of er rors was minimal when conflicts between the two hemi-figures were maxi mal. Moreover, perceptual conflicts, which mainly affect the perceptio n of the shape, appeared to influence the performance more than semant ic conflicts. Since the analysis of shape incongruency is probably acc omplished at early levels of information processing, the result sugges ts that preattentive analysis is largely spared in the experimental pa tients and that, in our task, bottom-up factors more than top-down fac tors modulate the expression of left neglect. (C) 1997 Elsevier Scienc e Ltd.