SYNAESTHESIA IN THE NORMAL LIMB

We explored the degree to which vision may alter kinaesthetic percepti on by asking participants to view their hand through a prism, introduc ing different horizontal deviations, while trying to align their finge rs above and below a thin table. When the visual image of one hand was displaced this overwhelmed kinaesthetic judgements and participants r eliably reported that they felt their limbs were aligned, even when th ey were laterally mis-aligned by as much as 10 cm. This effect, howeve r, was mediated by 'visual capture' and when the task was attempted in a darkened room with limb position indicated by an LED taped to the f inger, kinaesthesis dominated and participants reported that the LED s eemed to become detached from their finger tip. In both light and dark conditions the finger was clearly visible and only the background det ail was extinguished. Hence, in perceiving limb position, it appears t hat we believe in what we see, rather than in what we feel, when the v isual background is rich, and in what we feel when the visual backgrou nd is sparse.