Visual and haptic influence on perception of stimulus size.

In six experiments, subjects judged the sizes of squares that were presented visually and/or haptically, in unimodal or bimodal conditions. We were interested in which mode most affected size judgments in the bimodal condition when the squares presented to each mode actually differed in size. Three factors varied: whether haptic exploration was passive or active, whether the choice set from which the subjects selected their responses was visual or haptic, and whether cutaneous information was provided in addition to kinesthetic information. To match the task for each mode, visual presentations consisted of a cursor that moved along a square pathway to correspond to the haptic experience of successive segments revealed during exploration. We found that the visual influence on size judgments was greater than the influence of haptics when the haptic experience involved only kinesthesis, passive movement, and a visual choice set. However, when cutaneous input was added to kinesthetic information, size judgments were most influenced by the haptic mode. The results support hypotheses of sensory integration, rather than capture of one sense by the other.