Dissociable contributions of the two cerebral hemispheres to judgments of line orientation

A previous study of the performance of men with chronic unilateral focal brain lesions (due to wartime missile injury) on a standard test of line orientation suggested a left hemisphere (LH) as well as a right hemisphere (RH) contribution to visuospatial processing. The present study was designed to fractionate the variables that could underlie this unexpected finding and thereby to tease out the mechanisms involved in LH as compared with RH processing. A simpler (“purer”) version of the standard line orientation task was used, as were two other versions in which matching in an array and matching with distractors were measured. The findings confirmed the hypothesis of RH involvement in the purer task of metric measurement and suggested that the LH has an important role in keeping track of decisions and updating decisions in more complex aspects of line orientation judgment. ( JINS , 1996, 2, 335–339.)