NEURAL MECHANISMS OF SELECTION AND CONTROL OF VISUALLY GUIDED EYE-MOVEMENTS

The selection and control of action is a critical problem for both bio logical and machine animated systems that must operate in complex real world situations. Visually guided eye movements provide a fruitful an d 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 i n the frontal cortex that plays a central role in the production of pu rposive eye movements which is called the frontal eye field. A fundame ntal 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. Cu rrent evidence indicates that salient visual targets are located throu gh a temporal evolution of retinotopically mapped visually evoked acti vation. 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 ra te toward a fixed threshold to generate the gaze shift. For a given im age, the neural concomitants of perceptual processing occupy a relativ ely constant interval so that stochastic variability in response prepa ration introduces additional variability in reaction times. Neural pro cesses in another cortical area, the supplementary eye field, do not p articipate in the control of eye movements but seem to monitor perform ance. The signals and processes that have been observed in the cerebra l cortex of behaving monkeys may provide useful examples for the engin eering problems of robotics. (C) 1998 Elsevier Science Ltd. All rights reserved.