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Stephen Heinen, Elena Potapchuk, Scott Watamaniuk; Catch-up saccades during pursuit correct position error with the help of attention. Journal of Vision 2016;16(12):1353. doi: 10.1167/16.12.1353.
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© 2017 Association for Research in Vision and Ophthalmology.
Previously, we showed that more catch-up saccades occur when a pursuit stimulus has a central target than when it does not, and attending to the central target further increases saccade frequency (Heinen et al., VSS 2014; 2015). But why does this happen? Since retinal position and velocity errors contribute to catch-up saccade generation (deBrouwer et al., 2002), we sought to understand whether these factors are affected by the absence of a central pursuit target or varying attention demands. We first investigated the influence of a central target. Stimuli were either a single spot, four peripheral dots arranged in a virtual diamond, or a 5-dot composite of the two. Critically, all stimuli are symmetrical, and would create identical magnitude position and velocity errors on the retina if they were pursued equally well. Indeed, we found that position and velocity error were the same across all stimuli. However, position-error was a more potent saccade trigger for stimuli with foveal targets than those without. In the second experiment, we directed attention to and away from the fovea using a detection task in which either the central target or a peripheral one briefly dimmed. Again, position and velocity error were the same for all stimuli, and now, attention to the central target enhanced the influence of position error on saccade generation. Importantly, it was the relative contribution of position error to catch-up saccade generation that was greater for stimuli with a central target, and greater still when that target was attended. Conversely, removing the central target, or taking attention away from it, produced saccades driven primarily by velocity error. The results suggest that attention to a foveal target amplifies the position error signal during pursuit, and the system generates more catch-up saccades to correct this error.
Meeting abstract presented at VSS 2016
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