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Gregory J. Zelinsky, Andrei Todor; The role of “rescue saccades” in tracking objects through occlusions. Journal of Vision 2010;10(14):29. doi: 10.1167/10.14.29.
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© ARVO (1962-2015); The Authors (2016-present)
We hypothesize that our ability to track objects through occlusions is mediated by timely assistance from gaze in the form of “rescue saccades”—eye movements to tracked objects that are in danger of being lost due to impending occlusion. Observers tracked 2–4 target sharks (out of 9) for 20 s as they swam through a rendered 3D underwater scene. Targets were either allowed to enter into occlusions (occlusion trials) or not (no occlusion trials). Tracking accuracy with 2–3 targets was ≥92% regardless of target occlusion but dropped to 74% on occlusion trials with four targets (no occlusion trials remained accurate; 83%). This pattern was mirrored in the frequency of rescue saccades. Rescue saccades accompanied ∼50% of the Track 2–3 target occlusions, but only 34% of the Track 4 occlusions. Their frequency also decreased with increasing distance between a target and the nearest other object, suggesting that it is the potential for target confusion that summons a rescue saccade, not occlusion itself. These findings provide evidence for a tracking system that monitors for events that might cause track loss (e.g., occlusions) and requests help from the oculomotor system to resolve these momentary crises. As the number of crises increase with the number of targets, some requests for help go unsatisfied, resulting in degraded tracking.
Note: Values in parentheses indicate one standard error of the mean (SEM).
Note: The value under “Probed target” indicates the number of occlusions for the one target that was ultimately probed. Values in parentheses indicate one standard error of the mean (SEM).
Notes: (a) Too few NOEs existed in the Occlusion data for analysis. (b) OCEs are undefined in the No occlusion condition. Values in parentheses indicate a 95% confidence interval. OCE = occlusion event; NOE = near-occlusion event; POE = pre-occlusion event; BOE = before occlusion event.
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