FEF inactivation decreased ipsilesional and contralesional microsaccade peak velocities, both before and after cue onset.
(A) Unilateral (left) FEF inactivation reduced peak velocity for contralesional microsaccades independently of amplitude in our example monkey DZ and also decreased peak velocities for ipsilesional microsaccades. As shown in each inset, decreased peak velocities were associated with a downward shift in the main sequence relationship (+/- 95% confidence intervals). (B) FEF inactivation reduced peak velocity for microsaccades matched for radial amplitude, here shown for monkey DZ by averaging radial eye position and velocity traces (+/- standard error) aligned to microsaccade onset. As indicated by the shaded regions in A, we selected ipsilesional and contralesional microsaccades having radial amplitudes between 0.40° and 0.45°. The bilateral influence of FEF inactivation on amplitude-matched microsaccades is demonstrated by decreased peak velocity and increasing duration within the enlarged radial velocity traces (see arrows). (C) Peak velocity extracted at 2° decreased for contralesional microsaccades across monkeys and inactivation configurations and occasionally decreased for ipsilesional microsaccades. Distributions of peak velocities at 2° were obtained by bootstrapping 5,000 random samples of microsaccades and extracting the peak velocity at 2° from each linear regression. (D) Across monkeys, unilateral and bilateral FEF inactivation produced similar decreases in contralesional peak velocity at 2° in both the pre-cue and rebound periods. Filled symbols in C and D indicate statistically significant differences using a Welch's t test (p < 0.05) with 5,000 bootstrapped samples from each of the FEF warm and FEF cool conditions. Data in Supporting Information (see S2 Data).