The perceived position of the hand in space

This paper reports a series of experiments of the perceived position of the hand in egocentric space. The experiments focused on the bias in the propr ioceptively perceived position of the hand at a series of locations spannin g the midline from left to right. Perceived position was tested in a matchi ng paradigm, in which subjects indicated the perceived position of a target , which could have been either a visual stimulus or their own fingertip, by placing the index finger of the other hand in the corresponding location o n the other side of a fixed surface. Both the constant error, or bias, and the variable error, or consistency of matching attempts, were measured. Exp eriment 1 showed that (1) there is a far-left advantage in matching tasks, such that errors in perceived position are significantly lower in extreme-l eft positions than in extreme-right positions, and (2) there is a strong ha nd-bias effect in the absence of vision, such that the perceived positions of the left and right index fingertips held in the same actual target posit ion in fact differ significantly. Experiments 2 and 3 demonstrated that thi s hand-bias effect is genuinely due to errors in the perceived position of the matched hand, and not to the attempt at matching it with the other hand . These results suggest that there is no unifying representation of egocent ric, proprioceptive space. Rather, separate representations appear to be ma intained for each effector. The bias of these representations may reflect t he motor function of that effector.