Production, Control, and Visual Guidance of Saccadic Eye Movements
Figure 2
Pattern and timing of neural activity in FEF when mapping between location of visual target and endpoint of saccade is various. (a) Activity of FEF neuron with activity that can be identified with the allocation of attention (Type I). Average spike density function when the singleton fell in the neuron’s receptive field (thick line) and when the singleton was located opposite the receptive field (thin line) in prosaccade (top) and antisaccade (bottom) trials. Thick bar on abscissa marks range of RT. Scale bar represents 100 spikes/sec. (b) Activity of FEF neuron with activity that can be identified with selection of the saccade endpoint (Type II). (c) Cumulative distributions of modulation times in prosaccade (left) and antisaccade (right) trials for Type I (thin) and Type II (thicker) neurons with corresponding RT (thickest). The inset arrays indicate hypothesized functional correlates. After presentation of the array, selection of the singleton location occurs first in Type I neurons (indicated by the spotlight on the singleton); this occurs at the same time in prosaccade and antisaccade trials and does not relate to whether or when gaze shifts. In prosaccade but not antisaccade trials, Type II neurons select the singleton at a later time which accounts for some of the variability of RT. A comparison of activation in prosaccade and antisaccade trials reveals the time at which the shape of the singleton is encoded to specify the correct saccade direction; this follows singleton selection and coincides for Type I (thin blue) and Type II (thicker blue) neurons in antisaccade trials. At this moment in antisaccade trials, the representation of the singleton decreases, and the representation of the location opposite the singleton, the endpoint of the antisaccade increases (indicated by the weaker spotlight on the singleton and growing spotlight on the saccade endpoint). At this same time in prosaccade trials, the representation of the saccade endpoint is enhanced by the selection that occurs in the Type II neurons (indicated by the highlighted spotlight on the singleton). Subsequently, in antisaccade trials, the endpoint of the saccade becomes selected more than the location of the singleton by Type I (thin, red, dashed) and Type II (thicker red, dashed) neurons (indicated by the highlighted spotlight on the antisaccade endpoint). The time taken to select the endpoint of the saccade predicts some of the delay and variability of RT. Modified from Sato and Schall [163].
