The spatial characteristics of tactile form perception.

The perceived orientation of a raised letterform indenting the skin of the finger reverses (from normal to its mirror-image) when the letter is held in contact with the finger and both are rotated through 180 degrees about the axis of the finger. Thus, though the pattern of stimulated skin receptors remains constant, the perceived orientation of the letter reverses. On the basis of this observation it is proposed that tactual perception of object form involves assignment of a spatial coordinate system within which the patterns of skin stimulation are interpreted. In experiments in which the orientations of letters and subjects are systematically varied within the environment, the occurrence or nonoccurrence of reversal in perceived orientation of letters has been used to investigate the origin of the proposed spatial coordinate system; that is, whether it is assigned with respect to the observer ( egocentrically ) or with respect to the environment ( geocentrically ). The results indicate that the assignment of coordinates is determined by both egocentric and geocentric factors. It is proposed that the reversal phenomena observed in these experiments, and in experiments of others which involve drawing characters on the skin, are consistent with Gibson's proposal that it is object form which is directly perceived, but that this involves interpretation of the patterns of skin stimulation within a framework of spatial coordinates.