Visual attention during the preparation of bimanual movements.

We investigated the deployment of visual attention during the preparation of bimanually coordinated actions. In a dual-task paradigm participants had to execute bimanual pointing movements to different peripheral locations, and to identify target letters that had been briefly presented at various peripheral locations during the latency period before movement initialisation. The discrimination targets appeared either at the movement goal of the left or the right hand, or at other locations that were not movement-relevant in the particular trial. Performance in the letter discrimination task served as a measure for the distribution of visual attention during the action preparation. The results showed that the goal positions of both hands are selected before movement onset, revealing a superior discrimination performance at the action-relevant locations (Experiment 1). Selection-for-action in the preparation of bimanual movements involved attention being spread to both goal locations in parallel, independently of whether the targets had been cued by colour or semantically (Experiment 2). A comparison with perceptual performance in unimanual reaching suggested that the total amount of attentional resources that are distributed over the visual field depended on the demands of the primary motor task, with more attentional resources being deployed for the selection of multiple goal positions than for the selection of a single goal (Experiment 3).