Factors Influencing Haptic Perception of Complex Shapes.

Exploration of an object by arm movement and somatosensation is a serial process that relies on memories and expectations. The present experiments tested the hypothesis that this process involves breaking the object into component shapes (primitives). This was tested by having human subjects explore shapes composed of semicircular arcs, as well as quarter circles or quarter ellipses. The subjects' perception was reported using a visual display. In the first experiment, in which a series of semicircular arcs was presented, with offsets that differed from trial to trial, performance was consistent with the perception of two (left and right) semicircles. In the second experiment, subjects often failed to detect the quarter circles or quarter ellipses and again behaved as if the object was composed of two (top and bottom) semicircles. The results suggest that the synthesis of haptically sensed shapes is biased toward simple geometric objects and that it can be strongly influenced by expectations.