Predicted Position Error Triggers Catch-Up Saccades during Sustained Smooth Pursuit

Area of Science:

• Neuroscience
• Ophthalmology
• Visual Perception

Background:

• Human visual tracking involves smooth pursuit eye movements and catch-up saccades.
• The decision to trigger catch-up saccades involves a trade-off between position error tolerance and saccadic suppression.
• Previous research identified time windows where catch-up saccades are less likely, but the underlying mechanism remains unclear.

Purpose of the Study:

• To investigate the mechanistic explanation for saccade triggering during visual tracking.
• To test a stochastic decision model based on predicted position error (PEpred).
• To determine how saccade trigger timing and variability are affected by PEpred and visual uncertainty.

Main Methods:

• Utilized a double step-ramp task with human participants.
• Collected data on eye movements during visual tracking of moving stimuli.
• Analyzed saccade trigger times, position error (PE), predicted position error (PEpred), visual uncertainty (blurred targets), and retinal slip (RS).

Main Results:

• Large pre-saccadic PEpred (>10°) resulted in short saccade trigger times, irrespective of uncertainty.
• Small pre-saccadic PEpred (<10°) significantly increased saccade trigger time length and variability, especially with blurred targets.
• Increased signal-dependent noise (SDN) with higher retinal slip (RS) led to longer trigger times and more trials without saccades.

Conclusions:

• The findings support a predicted error-based decision process for coordinating saccades during smooth pursuit.
• The brain's saccade triggering mechanism appears to rely on probabilistic estimates of predicted position error.
• Visual uncertainty and the magnitude of predicted error critically influence the timing and occurrence of catch-up saccades.