Haptic perception disambiguates visual perception of 3D shape.

We studied the influence of haptics on visual perception of three-dimensional shape. Observers were shown pictures of an oblate spheroid in two different orientations. A gauge-figure task was used to measure their perception of the global shape. In the first two sessions only vision was used. The results showed that observers made large errors and interpreted the oblate spheroid as a sphere. They also misinterpreted the rotated oblate spheroid for a prolate spheroid. In two subsequent sessions observers were allowed to touch the stimulus while performing the task. The visual input remained unchanged: the observers were looking at the picture and could not see their hands. The results revealed that observers perceived a shape that was different from the vision-only sessions and closer to the veridical shape. Whereas, in general, vision is subject to ambiguities that arise from interpreting the retinal projection, our study shows that haptic input helps to disambiguate and reinterpret the visual input more veridically.