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Stephen Heinen, Jeremy Badler, Scott Watamaniuk; Pursuing an imaginary foveal stimulus increases catch-up saccades. Journal of Vision 2018;18(10):377. doi: 10.1167/18.10.377.
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Catch-up saccades during pursuit are thought to result from excessive position or velocity error. However, despite similar errors, a large pursuit target with an embedded foveal spot elicits more catch-up saccades than the large target alone. Furthermore, attending the embedded spot elicits more catch-up saccades than attending the large target. Here we ask if the higher frequency of catch-up saccades when attending the spot was mediated by the position error to the foveal target, or if attention at the fovea alone is sufficient to amplify the contribution of the saccadic mechanism. Observers pursued a stimulus composed of a 6° circular array of eight dots that traversed the screen at 10 deg/sec. In one condition, they detected a near-threshold luminance increase at a randomly selected peripheral dot that occurred at a random time on 50% of trials. In a second condition, observers detected a near-threshold stimulus that appeared in the center with the same frequency as the peripheral luminance change. An EyeLink 1000 recorded eye movements at 1000 Hz. We found that the catch-up saccade rate was higher when observers attended the center, even during epochs when no stimulus was present. Thus, foveating an imaginary stimulus still engaged the saccadic system. The results suggest that the frequency of catch-up saccades during pursuit in the absence of a foveal stimulus can reveal if attention is at the fovea. Furthermore, we find a similar result in our fixation data, evidence for a common mechanism subserving catch-up and micro saccades.
Meeting abstract presented at VSS 2018
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