Large scale differences between haptic and visual judgments of curvature

Large systematic scale differences show up when subjects are asked to match the curvature of a haptically presented surface with a visually presented cross section. Scaling factors ranging from 0.3 to 3.0 were found. Most often (for five out of six subjects) haptically estimated curvature was overestimated relative to visual curvature. We conclude that mutually inconsistent representations of surface curvature coexist in a single observer in the haptic and visual modalities. Another conclusion can be drawn with certainty, namely that at least one of the two modalities does not provide the observer with veridical information. The results for the left and the right hand of a subject were very similar, though for two subjects there existed a small significant difference in scaling. It seems likely that the curvature representations of the two hands are not independent of one another, but our data do not permit us to be conclusive