Hemispheric differences in the recognition of possible and impossible objects

Three experiments using a visual half-field technique were conducted to address the question of lateralised processing of three-dimensional aspects of visual stimuli. We used drawings of "possible" and "impossible" triangles and quadri laterals. In one condition subjects had to decide whether these stimuli were possible (i.e., the depicted figures could exist in the three-dimensional world) whereas in the second condition the task was to distinguish between triangular and quadrangular shapes. All experiments revealed an interaction of task and visual field on discrimination indices (d′) suggesting a dissociation of the processing of two- and three-dimensional aspects of visual stimuli. These results are discussed with respect to known perceptual differences between the cerebral hemispheres.