Abstract
We partially replicated and extended a study by Lederman and Abbott (1981, J Exp Psycho, 7(4), 902-915) who found that visual and tactile modalities contributed approximately equally to the visuo-tactile perception of surface texture. In a discrepancy paradigm, participants picked from sandpapers with grit values ranging from 40 (coarse) to 220 (fine) matches to visual (150 grit), tactile (60 grit), or discrepant visuo-tactile (150 & 60 grit) standards using vision, touch, or both modalities simultaneously (nine matches per participant). In our first experiment (N=12), we replicated Lederman and Abbott’s first experiment using a within-subjects design, instead of their between-subject design, to be able to evaluate interindividual differences in modality weights. Participants performed nine matches in separate sessions. In the second experiment, a subset of the same participants (N=10), repeated the first experiment but with the visual stimuli being illuminated from the side instead of from the top resulting in a modified appearance of the same visual stimuli. The first experiment showed that, on average, visual and haptic modalities contributed approximately equally to the visuo-tactile percept. This replicated the findings of Lederman and Abbott. We found considerable interindividual variations in the weights. Only two participants had almost equal weights while half of the others had higher visual and half had higher tactile weights. In the second experiment, we found similar average weights as before but the individual weights were consistently closer to equal modality weights. The grazing illumination increased the perceived coarseness of the visual stimulus and thus reduced the discrepancy between visual and tactile stimuli resulting in more consistent information. Our results demonstrate that visual and tactile information are weighted equally within a certain range of discrepancy. Outside this range, one of the modalities is weighted higher with no clear preference for either the visual or tactile modality.