Abstract
The ability to visually track, using smooth pursuit eye movements, moving objects is critical in both perceptual and action tasks. Here, by asking participants to view a moving target or track it with their hand, we tested whether different task demands give rise to different gaze strategies. We hypothesized that during hand tracking, in comparison to eye tracking, the frequency of catch-up saccades would be lower, and the smooth pursuit gain would be greater, because it limits the loss of stable retinal and extra-retinal information due to saccades. In our study participants viewed a visual target that followed a smooth but unpredictable trajectory in a horizontal plane and were instructed to either track the target with their gaze or with a cursor controlled by a manipulandum. Although the mean distance between gaze and target was comparable in both tasks, we found, consistent with our hypothesis, an increase in smooth pursuit gain and a decrease in the frequency of catch-up saccades during hand tracking. We suggest that this difference in gaze behavior arises from different tasks demands. Whereas keeping gaze close to the target is important in both tasks, obtaining stable retinal and extra-retinal information is critical for guiding hand movement.
Highlights
Many studies emphasize an intricate relationship between eye and hand movements[1]
When tracking the target with the hand, the lag and the distance between the cursor and target were substantially larger than the lag and distance between gaze and the target, indicating that eye tracking was more accurate than hand tracking
In contrast to previous suggestions that hand motion reinforces the internal representation of target motion[23,24], we suggest that differences in gaze behavior arises from different tasks demands
Summary
Many studies emphasize an intricate relationship between eye and hand movements[1]. For instance each time we initiate a reaching movement toward a spatial location, to grasp or touch an object, this movement is typically preceded by a saccadic eye motion toward the same spatial goal[2,3,4,5]. Previous studies in which participants were explicitly instructed to track the target simultaneously with their eyes and their hand have shown that, in comparison to pure eye tracking, the frequency of catch-up saccades decreases and the smooth pursuit gain increases[19,23,24]. It is not clear whether these effects are due to the demands of hand tracking per se, or arise because of the dual tracking participants are asked to perform. We felt it was important to document natural (spontaneous) gaze behavior during hand tracking, meaning in the absence of explicit requirements for gaze[15]
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