Psychophysical determination of coordinate representation of human arm orientation.

The coordinate representation of the sense of limb orientation was investigated psychophysically by asking subjects to match the orientation of the arm or of the forearm in several different coordinate representations. Movement of all degrees of freedom of one arm was permitted while movement of the other limb was restricted to the degree of freedom investigated in that particular experiment. Performance on the tasks was assessed by calculating the standard deviation of the difference in the angles of the two limbs. According to this criterion, we suggest that limb orientation is represented by the angular elevation of the limb and by the yaw angle, referred to a spatial reference frame.