Integration of visual and auditory spatial stimuli in the blind field of hemispherectomy patients

The effect of multisensory integration in the blind field of hemispherectomy patients was investigated in order to examine the possible involvement of the superior colliculus in blindsight. The superior colliculus may be responsible for residual abilities in the blind field because of its predominant subsidiary visual connections with the retina. Ten normal subjects and four patients with a temporal lobe removal served as controls for four experimental subjects (two hemispherectomized and two partial hemispherectomized). The experiment tested three tasks that measured reaction time and localization accuracy: (1) visual target only; (2) auditory target only; (3) simultaneous auditory and visual (aud/vis) stimuli at the same location. Only reaction time was measured in the condition where simultaneous presentations of aud/vis stimuli were made at different locations. The existence of blindsight was substantiated for localization, but not for reaction time in the blind field of hemispherectomy patients. None of the subjects demonstrated multisensory integration for reaction time and localization accuracy. Our results indicate that multisensory integration did not take place, at least with the types of stimuli used here. A role of the superior colliculus in blindsight remains possible since the hemispherectomy subjects still showed unconscious residual visual abilities in their blind field