Reference frames in the decisions of hand choice

Abstract

For the brain to decide on a reaching movement, it needs to select which hand to use. A number of body-centered factors affect this decision, such as the anticipated movement costs of each arm, recent choice success, handedness, and task demands. While the relative position of each hand to the target is also known to be an important spatial factor, it is unclear which reference frames coordinate the spatial aspects in the decisions of hand choice. Here, we tested the role of gaze- and head-centered reference frames in a hand selection task. With their head and gaze oriented in different directions, we measured hand choice of nineteen right-handed subjects instructed to make uni-manual reaching movements to targets at various directions relative to their body. Using an adaptive procedure, we determined the target angle that led to equiprobable right/left hand choices. When gaze remained fixed relative to the body, this balanced target angle shifted systematically with head orientation, and when head orientation remained fixed, this choice measure shifted with gaze. These results suggest that a mixture of head- and gaze-centered reference frames is involved in the spatially-guided decisions of hand choice, perhaps to flexibly bind this process to the mechanisms of target selection.