DOES MONOCULAR VIEWING IMPROVE TARGET DETECTION IN HEMISPATIAL NEGLECT

Experimental animals with large posterior-cortical lesions develop dis turbances of visual perception and visually-guided behavior in the con tralateral space, resembling the syndrome of unilateral spatial neglec t (USN) in humans. The visuo-motor performance in the ignored space is recovered some time following additional lesion inflicted to the cont ralesional superior colliculus (SC) or section of the intercollicular pathways. Based on the model that explains this recovery by disinhibit ion of the ipsilesional SC (the 'Sprague effect') Posner and Rafal [37 ] proposed that ipsilesional monocular occlusion could possibly reduce the 'tone' of contralesional collicular neurons thereby removing an i mportant contributor of hemineglect. A group of twenty-six right-hemis phere-damaged patients with USN was given a cancellation task under bi nocular and monocular (left and right) viewing conditions. Thirteen pa tients showed amelioration of left hemineglect in conditions of left-m onocular viewing, as compared to the baseline binocular state, Althoug h this result superficially resembles the Sprague effect, two patients benefited from right-monocular viewing whereas eleven patients showed no significant change in either right or left viewing conditions. The possible role of structures mediating interocular differences in targ et detection in cases of right hemisphere damage is discussed. It is s uggested that even if the Sprague effect contributes to the salubrious influence of monocular viewing it is hardly the single factor involve d.