Figure 2.

Saccades evoked by microstimulation in example sites in the superior colliculus. (A) Average saccade vectors evoked by low (red) and high (blue) frequency microstimulation in an example site in the SC. Vectors are the average of all the evoked saccades for each of the fixation LED locations. Circles indicate average startpoints; arrowheads average endpoints. (Missing data at some fixation positions is due to a combination of the random-with-replacement selection of fixation positions and the somewhat probabilistic evocation of saccades, especially at low frequencies; trials in which no saccade was produced were excluded from this analysis.) (B) Average saccade vectors for each fixation LED location (color-coded) evoked by low (upper panel) and high (lower panel) frequency microstimulation in the same site as shown in (A). Saccade vectors are aligned on a common origin to highlight the differences in vector as a function of initial eye position (indicated by color). Saccades evoked by both high- and low frequency stimulation showed an effect of initial eye position, but the effect was larger for low frequency stimulation. (C) Amplitude of individual saccades evoked by low and high frequency microstimulation in the same site as shown in (A,B), as a function of initial eye position. Lines show linear regression through the data. Each data point represents a single saccade (D–F). Same as (C), for three additional sites. The low frequency regression fits are significant for all sites illustrated (p < 0.0001); the high frequency regression fits are significant in (C,F) (p < 0.0001).