A role for the left hemisphere in spatial processing.

This study extended our recently reported evidence of a left hemisphere (LH) contribution to spatial processing on standard visuospatial tasks. The present investigation compared performance on these standard tasks with that on 'purer' experimental tasks. Two tasks of line orientation, two of shape rotation and a shape matching task were administered to 50 men with stable unilateral post-Rolandic missile injuries and 32 control subjects. A LH deficit was found on the standard task of line orientation but not the 'purer' task, suggesting that the LH plays a role in eliminating extraneous information, presented only in the standard test. As for shape rotation, the LH group was impaired on both tasks. On the shape matching task, both experimental groups were significantly slower than control subjects. It is proposed the LH makes an important contribution to mental rotation and the understanding of Euclidean geometrical shapes.