We used three lines of inquiry to determine how the cerebral cortex and its efferent regions control eye movement and visuospatial attention. The first was a psychophysical study to quantify visual attention in the monkey. We used as an operational definition of attention the process that chooses the location in space at which the perceptual threshold as lowest, and then developed a psychophysical paradigm to assess it in monkeys. Rhesus monkeys were trained to perform a memory-guided delayed saccade task, in which they had to remember the location of a briefly flashed stimulus and later make a rapid eye movement (saccade) to the spatial location of that stimulus when a fixation point disappeared. If the monkeys saw a no-go stimulus at any time during the experiment they were rewarded for holding fixation and not making the saccade. We varied the brightness of the no-go to determine the threshold for its perception, and then saw what factors affected that threshold. When a monkey is planning a saccade to a spatial location, the perceptual threshold is lower at that location than at other peripheral position in the visual field. When an object flashes elsewhere in the visual field within 100 ms the perceptual threshold becomes low at the spatial location of the flash, and rises at the spatial location of the saccade target. It takes nearly a second for the low threshold to return to the spatial location of the saccade threshold. These experiments prove that monkeys have a process similar to the human ‘spotlight of attention’, and that attention is usually, but not exclusively, linked to the process of making a saccadic eye movement. The second was an analysis of the effect of small reversible lesions of monkey lateral intraparietal area on a number of tasks, including a detection task, and antisaccade task, and a landmark task. In the detection task the monkeys ad to detect the appearance of a cue which told them what rapid eye movement (saccade) to make. Monkeys had difficulty detecting the stimulus in the visual field contralateral to the lesion. In the antisaccade task the monkeys had difficulty no difficult making the saccade when the saccade goal was in the visual field affected by the lesion, but had great difficulty making the saccade when the cue was in the visual field affected by the lesion. Monkeys were also trained on choosing a cue that was closest to a landmark. Lateral intraparietal lesions did not seem to be affected by this task. These results, together with the psychophysical results above, suggest that lateral intraparietal cortex is important in guiding visual attention, but may be less important in driving saccades. The third was an analysis of activity of neurons in the monkey dorsolateral prefrontal cortex in a self-ordered task. This task requires that the monkey monitor its own behavior- remember what choices it made. It is a difficult task and the monkeys perform it in streaks. Neurons in prefrontal cortex track the probability of the monkeys’ success in the task with a significant time-lag or time-lead, of the order of two minutes, as well as responding to the specifics of the task itself. T
