The spatiotemporal characteristics of the attentional shift relative to a reach.

While the attentional shift preceding a saccadic eye movement has been well documented, the mechanisms surrounding the attentional shift preceding a reach are not well understood. It is unknown whether these mechanisms may be the same as those used in perceptual tasks, or those used in the planning of a saccade. We mapped the spatiotemporal properties of attention relative to a reach to determine the time course of attentional facilitation for hand movements alone. Participants had to reach toward a target and during the reach a perceptual probe could appear at one of six locations around the target, and at nine temporal offsets relative to the cue. Results showed a consistent pattern of facilitation in the planning stages of the reach, with attention increasing and then reaching a plateau during the completion of the movement before dropping off. These results demonstrate that planning a hand movement necessitates a shift in attention across the visual field around 150 ms before the onset of a reach. While these results are broadly consistent with the results of experiments mapping attentional shifts for saccades, the spatiotemporal profile of facilitation found shows that reaching without a concurrent eye movement also causes shifts in attention across the visual field. These results also suggest that the profile of the attentional shift preceding and during a hand movement is different at different locations across the visual field.