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

2019; Society for Neuroscience; Volume: 7; Issue: 1 Linguagem: Inglês

10.1523/eneuro.0196-18.2019

2373-2822

Omri Nachmani, Jonathan Coutinho, Aarlenne Z. Khan, Philippe Lefèvre, Gunnar Blohm,

Motor Control and Adaptation

Abstract For humans, visual tracking of moving stimuli often triggers catch-up saccades during smooth pursuit. The switch between these continuous and discrete eye movements is a trade-off between tolerating sustained position error (PE) when no saccade is triggered or a transient loss of vision during the saccade due to saccadic suppression. de Brouwer et al. (2002b) demonstrated that catch-up saccades were less likely to occur when the target re-crosses the fovea within 40–180 ms. To date, there is no mechanistic explanation for how the trigger decision is made by the brain. Recently, we proposed a stochastic decision model for saccade triggering during visual tracking (Coutinho et al., 2018) that relies on a probabilistic estimate of predicted PE (PE pred ). Informed by model predictions, we hypothesized that saccade trigger time length and variability will increase when pre-saccadic predicted errors are small or visual uncertainty is high (e.g., for blurred targets). Data collected from human participants performing a double step-ramp task showed that large pre-saccadic PE pred (>10°) produced short saccade trigger times regardless of the level of uncertainty while saccade trigger times preceded by small PE pred (<10°) significantly increased in length and variability, and more so for blurred targets. Our model also predicted increased signal-dependent noise (SDN) as retinal slip (RS) increases; in our data, this resulted in longer saccade trigger times and more smooth trials without saccades. In summary, our data supports our hypothesized predicted error-based decision process for coordinating saccades during smooth pursuit.