Collicular function in human vision.

Threshold elevation in the periphery of the visual field as a consequence of repetitive stimulation can be abolished by stimulating a mirror-symmetric position in the contralateral visual half-field. A patient suffering from a congenital malformation of the right superior colliculus did not exhibit threshold elevation when stimulated repeatedly in the left visual field. Stimulation in the right visual half-field resulted in the usually observed threshold elevation, but stimulating a mirror-symmetric position in the left visual half-field did not abolish threshold elevation in the right half-field. These observations suggest that: (a) threshold elevation probably occurs as a consequence of collicular adaptation and (b) the mirror-symmetrically organized interhemispheric interaction is mediated at the collicular level.