Neural mechanisms of selection and control of visually guided eye movements.

The selection and control of action is a critical problem for both biological and machine animated systems that must operate in complex real world situations. Visually guided eye movements provide a fruitful and important domain in which to investigate mechanisms of selection and control. Our work has focused on the neural processes that select the target for an eye movement and the neural processes that regulate the production of eye movements. We have investigated primarily an area in the frontal cortex that plays a central role in the production of purposive eye movements which is called the frontal eye field. A fundamental property of biological nervous systems is variability in the time to respond to stimuli. Thus, we have been particularly interested in examining whether the time occupied by perceptual and motor decisions explains the duration and variability of behavioral reaction times. Current evidence indicates that salient visual targets are located through a temporal evolution of retinotopically mapped visually evoked activation. The responses to non-target stimuli become suppressed, leaving the activation representing the target maximal. The selection of the target leads to growth of movement-related activity at a stochastic rate toward a fixed threshold to generate the gaze shift. For a given image, the neural concomitants of perceptual processing occupy a relatively constant interval so that stochastic variability in response preparation introduces additional variability in reaction times. Neural processes in another cortical area, the supplementary eye field, do not participate in the control of eye movements but seem to monitor performance. The signals and processes that have been observed in the cerebral cortex of behaving monkeys may provide useful examples for the engineering problems of robotics.