HAPTIC UNDERESTIMATION OF ANGULAR EXTENT

To what extent can individuals accurately estimate the angle between t wo surfaces through touch alone, and how does tactile judgment compare to visual judgment? Subjects' ability to estimate angle size for a va riety of haptic and visual stimuli was examined in a series of nine ex periments. Triangular wooden blocks and raised contour outlines compri sing different angles and radii of curvature at the apex were used in experiments 1-4 and it was found that subjects consistently underestim ated angular extent relative to visual baselines and that the degree o f underestimation was inversely related to the actual size of the angl e. Angle estimates also increased with increasing radius of curvature when actual angle size was held constant. In contrast, experiments 5-8 showed that subjects did not underestimate angular extent when asked to perform a haptic-visual match to a computerized visual image; this outcome suggests that visual input may 'recalibrate' the haptic system 's internal metric for estimating angle. The basis of this crossmodal interaction was investigated in experiment 9 by varying the nature and extent of visual cues available in haptic estimation tasks. The addit ion of visual-spatial cues did not significantly reduce the magnitude of haptic underestimation. The experiments as a whole indicate that ha ptic underestimations of angle occur in a number of different stimulus contexts, but leave open the question of exactly what type of visual information may serve to recalibrate touch in this regard.