A hybrid frame of reference for visuo-manual coordination.

Visuo-kinesthetic matching of the orientation of an object in three-dimensional space has been studied by asking normal human subjects to align their unseen hand in parallel to the perceived orientation of a virtual stereoscopic object. Systematic errors were found for all three degrees of freedom of object orientation. These errors were much reduced when vision of the hand was allowed. The analysis of the distribution of the directional components of the errors revealed that matching performance without view of the hand was biased in a preferred direction that coincides with neither anatomical axes of the hand nor earth-fixed axes of visual space, but is intermediate between hand space and visual space. This suggests that a hybrid frame of reference is constructed by combining parallel multisensory information.