Gaze-related functions driving gaze anchoring in reaching

Abstract

When reaching to a target, we typically direct our gaze to the target throughout the reach. If a secondary saccade target is presented during the reach, and we are instructed to shift our gaze to this target, the gaze shift is generally delayed until 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 reached with their right hand and were instructed to both shift their gaze and move their left hand to the secondary target as soon as it appeared. We found that, during the reaching movement, gaze was anchored to the target for both visual and visual-haptic targets. In the visual-haptic condition, gaze appeared to be anchored during the initial directing phase of the reach during which peripheral vision directs the hand to the vicinity of the target. In the visual condition, gaze appeared to be anchored during both the directing phase and subsequent guiding phase during which central visual guides the hand. 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. New & NoteworthyWhen reaching to a visual target, gaze is typically anchored to the target even when a competing saccade target appears. We show that anchoring also occurs for visual-haptic targets but is limited to the initial phase of the reach, likely because vision is not required to confirm target attainment. In contrast to gaze, anchoring is not observed for the non-reaching hand, which can begin moving to a competing target as soon as it appears.