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Scott Watamaniuk, Elena Potapchuk, Japjot Bal, Stephen Heinen; Interactions between fixation and pursuit systems. Journal of Vision 2015;15(12):1020. doi: 10.1167/15.12.1020.
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© ARVO (1962-2015); The Authors (2016-present)
Previous work suggested that the pursuit and fixation systems are separate (e.g., Luebke & Robinson, 1988). Here we present evidence of interactions between these two systems. In separate blocks of trials, observers either pursued a spot that started at the edge of the display and moved across the screen at a constant velocity on every trial, or did so with randomly interleaved fixation trails. When fixation trials were included, anticipatory pursuit was reduced relative to when only pursuit trials were present. This suggested an active inhibition of pursuit by the fixation system. Alternatively, inserting the fixation trials may have simply allowed time for a stored velocity signal thought to drive anticipatory pursuit (e.g., Barnes & Asselman, 1991) to dissipate. To test this, we interleaved ‘blank’ trials (no stimulus), of the same duration as the fixation trials, with the pursuit trials. Anticipatory pursuit was high under this condition, suggesting that fixation trials actively inhibit anticipatory pursuit. If so, why does the fixation period that typically precedes movement of the target in pursuit trials not have the same inhibitory effect? One possibility is that separate fixation trials introduce uncertainty about whether the stimulus will move or not. To test this, we manipulated the level of uncertainty by changing the proportion of fixation trials within a block. We found that anticipatory pursuit decreased as the proportion of fixation trials increased, suggesting that uncertainty about whether the target will move plays a role. However, we also found that pursuit latency increased as the proportion of fixation trials increased, consistent with an active interaction between fixation and pursuit circuitry.
Meeting abstract presented at VSS 2015
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