“Extinction” to bilateral simultaneous stimulation in the monkey

PATIENTS WITH neurological symptoms frequently show a form of sensory deficit which has interested physiological psychologists as much as clinical neurologists.]-5 In the classical case, the patient presenting signs of unilateral cerebral hemisphere damage will perceive a stimulus to the sensory field on the side opposite the lesion but will fail to perceive it if the opposite homologous field is stimulated simultaneously. This phenomenon has been termed “inattention” by Critchley,z which suggests an explanatory bias, and “extinction” by Bender,’ the latter label being more neutral and arbitrarily adopted by us. Extinction has been observed in the tactile, visual, auditory, and gustatory modalities.’ It can occur in patients with cerebral tumors,e penetrating wounds, vascular accidents, demyelinating diseases, and other destructive lesions.’ Localization of the causative lesion is not restricted to the cortex or to any particular lobe, although Critchley has commented that tactile extinction is more commonly observed with right parietal lesions. Explanatory concepts have invoked the factors of attention2 and perceptual rivalry,? but neither of these approaches fully explains the physiological or psychological mechanisms involved. In order to study extinction in the experimental laboratory and to determine whether it is contingent upon parietal injury, we have attempted to simulate this phenomenon in the monkey.