Laterality effects for simple and complex geometrical figures, and nonsense patterns.

Three groups of normal, right handed subjects were trained to give same-different responses to pairs of stimuli presented simultaneously to the right or the left side of a fixation point. The subjects exhibited faster reactions (pressing 1 of 2 keys) to stimuli appearing in the right visual field when the stimuli were simple geometrical figures (e.g. triangles and squares) or nonsense patterns. By contrast, drawings subjects showed a left visual field advantage when the stimuli were complex geometrical figures (e.g. 10 and 11 sided regular polygons). These differences in performance for the 2 halves of the visual field are attributed to differential hemispheic specializations. The opposite hemispheric superiorities found with different classes of stimuli are in turn attributed to the discrimination of single features by the left hemisphere and to the use of a spatial strategy by the right hemispher