Discharge of superior collicular neurons during saccades made to moving targets

Abstract

1. The discharge of neurons in the deeper layers of the monkey superior colliculus was recorded during saccades made to stationary and to smoothly moving visual targets. 2. All neurons that discharged for saccades made to stationary targets also discharged during saccades made to moving targets, but there was a systematic shift in the saccade vector yielding maximal activity (i.e. center of the movement field) of collicular neurons for the latter class of movements. The shift moved the center of the movement fields toward larger-amplitude pursuit saccades for target motion away from the fovea, in comparison with saccades made to stationary targets. However, the discharge at the center of the movement field for pursuit saccades was 14% lower when averaged over the sample of recorded cells. 3. The saccades made during pursuit tracking of moving visual stimuli have different dynamics than saccades made to stationary targets. At similar amplitudes pursuit saccades are slower, and their velocity profiles often show secondary velocity peaks or inflection points and have longer-duration decelerating phases. 4. The combined experimental observations of a change in saccade dynamics and the shift in movement fields in collicular neurons for pursuit saccades are compatible with the hypothesis that saccades made to moving targets are controlled by neural processing in two partially separate pathways. In this theory, one path is concerned with correction of a presaccadic retinal position error (a path that includes the colliculus) and another path is concerned with position extrapolations based on the velocity of the moving target (a path that does not include the colliculus).

Saccadic Interception of a Moving Visual Target after a Spatiotemporal Perturbation

“…The first signal would encode the location where the target is initially detected (snapshot) and the second signal would encode its subsequent displacement on the basis of target motion signals (Keller et al, 1996;Optican, 2009). Yet this dual drive hypothesis raises several problems.…”

Discharge of Monkey Nucleus Reticularis Tegmenti Pontis Neurons Changes During Saccade Adaptation

“…1B) or saccades in nonpreferred directions (not shown). Plots of the number of spikes versus either saccade-or "desired saccade-" (i.e., target position-initial eye position) amplitude were fit by linear regression for open movement fields and by a spline fit for closed movement fields as has been done by others (Keller et al 1996;Soetedjo et al 2002b). …”

Neural dynamics of saccadic and smooth pursuit eye movement coordination during visual tracking of unpredictably moving targets

“…The saccadic system appears to use target velocity information to calibrate the amplitude of the catch-up saccade. After establishing that SC firing specified equivalent amplitudes for two saccades of unequal amplitudes made to a moving or to a stationary target, Keller, Gandhi and Weir (1996) hypothesized that the trans-SC path (SC to PPRF, Figure 1b), which programs a saccade solely on the basis of the pre-saccadic gaze-position error, is assisted by another path that corrects the programmed saccade by using information about the speed of the moving target. In the model, speed-tuned extra-foveal MT cells project to the cerebellum via DLPN (Figure 1a), and error-guided cerebellar learning across trials converges to the correct gain for relating saccadic size increments to target velocity.…”