The role of frontal eye-fields and superior colliculi in visual search and non-visual search in rhesus monkeys.

Rhesus monkeys were tested on a visual search task in which they had to find and retrieve a peanut from a display of visually similar but inedible objects. The speed with which they did so was measured. Animals in which the superior colliculi or frontal eye-fields had been removed took longer to find the peanut than two operated control groups. Animals with collicular lesions had longer latencies than those with frontal eye-fields removed. These two groups were also tested on a second task, non-visual search, in which a peanut was concealed in each of 25 identical holes. The animals' task was to retrieve all 25 peanuts as quickly as possible. The group with frontal eye-fields removed made significantly more return errors, i.e. returning to a hole already sampled, than the control group but, in contrast to the first task, the animals with collicular lesions were not impaired. The results are related to the physiological properties of frontal eye-fields and superior colliculi and to the effects of frontal cortical brain damage in man. It is suggested that the frontal eye-fields are concerned with internally organized, i.e. voluntary, eye scanning whereas the superior colliculi are concerned with the detection and location of targets which are then fixated involuntarily.