We analyzed the pursuit velocity modulation by the flashed Gabor patch as a function of the spatial frequency (see Experiment 1 in the Methods) following the saccade analysis above. We extracted the pursuit eye velocity only from the horizontal eye position, after saccade and blink removal, and explored its properties regarding latency and peak velocity (see the Methods). The results of the spatial frequency experiment appear in
Figure 4. As shown in
Figure 4b, the eye velocity was modulated around the time of the flashed Gabor (100 ms in blue shade); the horizontal velocity decreased to a minimum of around 200 ms and then increased to a maximum of around 400 ms. This modulation was related to the Gabor spatial frequency, with a strong modulation for low frequencies (e.g., 1 cyc/°) and a weak modulation for high frequencies (e.g., 8 cyc/°).
Figures 4c-
4e shows the pursuit latencies and the peak velocity as a function of spatial frequency in specific time windows derived from the continuous velocity modulation function (
Figure 4b): 100 to 400 ms for the inhibition and 300 to 700 ms for its release. As shown (
Figures 4c–
4e), the latency of the minimum and maximum velocity peaks increased, and the maximum velocity decreased with increased spatial frequency. The related effect on the minimum velocity was insignificant (data not shown). The LMM analysis revealed the same effect, with β
1 = 1.47 (0.83,2.12),
SE = 0.33, and
t(118) = 4.50 at the minimum velocity latency window (4c), β
1 = 1.84 (1.05,2.62),
SE = 0.39, and
t(118) = 4.64 in the maximum velocity latency window (4d), and β
1 = −0.05 (−0.07, −0.04),
SE = 0.009, and
t(118) = −6.10 in the peak velocity window (4e); all
p values of the LMM model were significant (
p < 0.005), indicating that a nonzero linear relationship exists between the pursuit latencies and the maximum pursuit velocity for the spatial frequencies tested. The correlation of the mean results were all linear for the group averages: for the minimum velocity latency (r
2 = 0.96), the maximum velocity latency (
r2 = 0.92), and the peak velocity (
r2 = 0.91), the p-values of the correlations were all found to be significant (
p < 0.005). The nonparametric permutation test revealed additional significant results, with
pmc = 0.001 in the minimum velocity latency,
pmc = 0.001 in the maximum velocity latency, and
pmc = 0.002 in the peak velocity.