EXPRESS: Activation of the Motor System Following Gaze Cues is Determined by Hand Access, Not Hand Proximity.

The influence of gaze cues on target prioritization (reaction times (RTs)) and movement execution (movement trajectories) differs based on the ability of the human gaze cue model to manually interact with the targets. Whereas gaze cues consistently impacted RTs, movement trajectories may only be affected when the hands of the human model had the potential to interact with the target. However, the perceived ability to interact with the targets was confounded by the proximity between the model's hands and the targets. The current study explored if the influence of gaze cues on movement trajectories is shaped by the model's potential to access and interact with the targets using their hands or simply the proximity of the hands. A centrally presented human model randomly gazed towards one of two peripheral target locations. Participants executed aiming movements to targets that non-predictively appeared at one location at a stimulus onset asynchrony of 100, 350, or 850 ms. In Experiment 1, the model's hands could not directly access the targets as each was holding a tray. In Experiment 2, the hands had direct access to the targets, but their palms-downwards orientation and wrist-flexed posture rendered efficiently interacting with the targets unlikely. Although RTs showed a facilitation effect of the gaze cue in both experiments, changes in movement trajectories were only observed when the model had direct access to the target (Experiment 2). The results of the current study suggest that the gaze model's direct hand access is necessary for the social gaze cues to influence movement execution.