The effects of bilateral frontal eye-field, posterior parietal or superior collicular lesions on visual search in the rhesus monkeys.

Superior collicular, frontal eye-field and posterior parietal lesions increased the time taken to find a circular target among other geometrical shapes. The collicular monkeys were considerably more impaired than the other groups, suggesting that the superior colliculus is the main neural structure underlying this highly practised visual search task. Failure to respond in the 5 sec allowed on each trail increased for all groups, and the collicular and frontal groups showed a small increase in false positive errors. None of the groups increased search time for a near-threshold target on a homogenous background. [corrected] Analysis of the latencies of individual trials suggest that scanpaths over the display were still systematic after the lesions. This suggests that the search was being slowed down either by the need to make more correction saccades to give accurate fixations of the stimuli being discriminated, or by an increase in latencies specificially for those saccades that shift the gaze between stimuli.