Figure 1

(a) Main-sequence relation of peak eye-velocity vs. saccade amplitude of monkey saccades for visually evoked (V-)saccades (dots) and for saccades elicited by electrical microstimulation at a single site in the superior colliculus at various current strengths (E-saccades; squares). The stimulation site in the motor map corresponded to a saccade amplitude of about 15 deg. For high stimulation currents, E-saccades and V-saccades had the same kinematics (large red dot). For the low stimulation currents at the site, two effects were observed: (i) evoked saccade amplitudes decreased, and (ii) evoked peak velocities decreased too, but fell systematically below the V-saccade main-sequence relation. Data adapted from³⁶. (b) Human main-sequence relation for fast V-saccades (data points near the red curve) and for slow V-saccades, due to an intraveneous injection of diazepam, and fatigue. Data adapted from².