Haptic underestimation of angular extent.

To what extent can individuals accurately estimate the angle between two surfaces through touch alone, and how does tactile judgment compare to visual judgment? Subjects' ability to estimate angle size for a variety of haptic and visual stimuli was examined in a series of nine experiments. Triangular wooden blocks and raised contour outlines comprising different angles and radii of curvature at the apex were used in experiments 1-4 and it was found that subjects consistently underestimated angular extent relative to visual baselines and that the degree of underestimation was inversely related to the actual size of the angle. 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 cross-modal interaction was investigated in experiment 9 by varying the nature and extent of visual cues available in haptic estimation tasks. The addition of visual-spatial cues did not significantly reduce the magnitude of haptic underestimation. The experiments as a whole indicate that haptic 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.