Lateralised perception of bilateral chimaeric faces by normal subjects

Abstract

A COMPOSITE ‘chimaeric’ figure is one constructed by abutting two different half-figures along a vertical join. Following surgical section of the pathways connecting the two cerebral hemispheres (the commissures), patients subjectively experience a compelling perceptual ‘completion’ in their perception of both halves of such figures when presented at the midline of vision. This perceptual completion evidently occurs independently in each of the two cerebral hemispheres¹. The critical condition for this phenomenon might be the disconnection between the primary visual cortices of the two hemispheres. Only those portions of these cortical areas are cross-connected which represent a narrow strip of the visual field in the region of the vertical midline². We, therefore, tested normal subjects with chimaeric faces in which no vertical join was visible. Our subjects then experienced perceptual completion, as we had predicted.