The experiments described in the chapter concentrates on one subdivision of posterior parietal cortex, the lateral intra parietal area (LIP), which is defined on the basis of its projections from the frontal eye field and which projects to the superior colliculus. This area, placed in a network concerned with orienting, eye movement, and visual attention has seemed to be ideal for a role in spatial analysis and the generation of saccades. These experiments attempt to understand the function of LIP by studying single neurons in this area using a large series of tasks designed to isolate various aspects of spatial analysis. Three conclusions are derived: (1) single LIP neurons receive several different extra-retinal inputs; (2) LIP neurons signal the distance and direction of a spatial location from current or anticipated center of gaze; and (3) this signal can be instantaneously accurate. Enhancement is a general phenomenon in LIP. Analysis of the population of LIP neurons reveals that the great majority of cells give an enhanced response when the stimulus is of importance to the monkey. The independence of enhancement from the monkey's response mode led to the suggestion that all of the activity in the parietal cortex during saccade tasks could be explained as an enhancement of the visual response. © 1993, Academic Press Inc.
