The effect of ablation of frontal eye-fields and superior colliculi on visual stability and movement discrimination in rhesus monkeys.

The neurological basis of the maintenance of a stable visual scene by means of a corollary discharge mechanism was investigated. Monkeys were trained to detect and respond to sudden rapid movement of a small spot of light in an otherwise totally dark environment. There was no evidence that after removal of the frontal eye-fields, superior colliculi, or caudal superior temporal sulcus the animals confused real movement of the target with retinal image movement caused by changing the position of head and eyes. The result was confirmed by an examination of the ipsiversive turning that follows unilateral frontal eye-field or collicular ablation. If the turning is a compensation for apparent movement of the visual world when the eyes are moved it should not be present in total darkness. It was still present. The thresholds for the smallest detectable instantaneous displacement of the target were also measured. The threshold was impaired by bilateral superior colliculus lesions but not by removal of the frontal eye-fields or cortex of the caudal part of the superior temporal sulcus.