Gaze-related functions driving gaze anchoring in reaching
In an everyday task, such as planting spring flowers, the eyes typically fixate target objects that we manipulate. When reaching to a target object, gaze shifts away from the reach target to a secondary saccade target, presented during the reach, are delayed until after the reach target has been attained--a phenomenon known as gaze anchoring. Here, we compared gaze anchoring in human participants when reaching to a visual target versus a visual-haptic target providing force feedback upon contact. We also examined gaze anchoring in a bimanual context in which participants were instructed to shift their gaze to the secondary saccade target as soon as it appeared and, at the same time, move their other hand to the secondary saccade target. We found that, during the reaching movement, gaze was anchored to the target for both visual and visual-haptic targets. Whereas in the visual condition gaze appeared to be anchored until the end of the reaching movement, in the visual-haptic condition, gaze appeared to be anchored until the hand was close to the target (i.e., the end of the directing phase). In two-handed reaching, gaze anchoring was observed but anchoring did not extend to the left hand, which started moving before the eyes. Overall, our findings indicate that the timing of eye and hand movements in object manipulation is linked to the function of target fixations.