PERCEPTION OF MOTION-IN-DEPTH IN PATIENTS WITH PARTIAL OR COMPLETE CEREBRAL HEMISPHERECTOMY

Four patients with functional hemispherectomy, one patient with a comp lete anatomical hemispherectomy, and one patient with unilateral remov al of the temporal, parietal and occipital lobes took part in two sets of experiments designed to investigate their residual sensitivity to motion-in-depth in the hemianopic visual field. Two types of computer- generated visual displays were used; in the first set of experiments, a dot pattern and in the second, a circular checkerboard. These simula ted either convergent, divergent or reversed rotational motion. Each s et of experiments consisted of two parts; in the first part, electrode rmal responses were monitored during stimulus presentation while the s ubjects performed a simple distracting task. In the second part, subje cts were asked to state verbally the direction of stimulus motion. Con trary to expectations, no reliable changes in skin conductance were el icited from any of the subjects by changes in the direction of motion of the component parts of either the dot pattern display or the circul ar checkerboard display. Furthermore, none of the subjects were able t o discriminate the direction of motion of the target patterns when pre sented in the hemianopic held. The most parsimonious explanation is th at the subcortical visual pathways which survive hemispherectomy are u nable to process visual information relating to motion in depth.