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Marius Blanke, Jonas Knöll, Frank Bremmer; Localization of visual targets during open-loop smooth pursuit. Journal of Vision 2012;12(9):990. doi: 10.1167/12.9.990.
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Numerous studies in recent years have shown that eye movements induce errors in the localization of briefly flashed stimuli. Smooth pursuit and the slow phases of optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN) are different forms of so-called slow eye-movements. Pursuit is induced by the movement of a small target whereas large field motion induces a reflexive alternation of slow- and fast phases, the so-called OKN. Finally, OKAN is observed in total darkness after prolonged OKN. Accordingly, OKAN is considered an open-loop eye movement. During pursuit and OKN, perceived flash positions are shifted in the direction of the slow eye movement. During OKAN, however, localization has a foveofugal bias. Here, we examined flash localization during open-loop pursuit and asked, whether localization is prone to errors and whether this error is similar to the one found during visually guided smooth pursuit or during OKAN. Human subjects tracked a pursuit target. In half of the trials, the target was extinguished for 300 ms during the steady-state, inducing open-loop pursuit. Flashes were presented during this gap (gap condition) or during steady-state pursuit (control condition). In both conditions, perceived flash locations were shifted in the direction of the eye movement. While error patterns were similar in both conditions, shifts were slightly, yet significantly, smaller in the gap condition. During steady-state and gap-pursuit, localization error did not correlate with eye velocity. Precision of localization changed for stimuli presented during the gap. Compared to steady-state, it decreased ahead of target and increased in its wake. This concurs with a widening of the attentional spotlight during gap-pursuit. Considering that mislocalization was not correlated with eye velocity and that the mislocalization pattern during open-loop pursuit was steady-state pursuit-like rather than OKAN-like, we suggest that an internal representation of the pursuit target contributes to mislocalization during open-loop pursuit.
Meeting abstract presented at VSS 2012
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