Perception of the tactile texture of raised-dot patterns: further evidence of an opponent process in the sense of touch.

Observers judged the tactile dissimilarities of raised-dot surfaces presented in pairs. The role of the SA I channel in determining these tactile dissimilarities was investigated by examining the dissimilarity judgments when this channel was adapted and when it was not. In an earlier study, the role of the PC channel in determining tactile dissimilarity was examined using the same stimulus materials when the PC channel was adapted and when it was not. Three orthogonal perceptual dimensions identified as blur, pattern roughness, and clarity were found using ALSCAL multidimensional analysis to account for the judged dissimilarities. The same three dimensions were found again in the present study. The dimensions of blur and pattern roughness were unaffected by adaptation of either the SA I or the PC channel. The finding of no effect of adaptation of the SA I channel on either of these two dimensions suggests that the roughness of the macrostructure of a textured surface is coded by the relative rather than by the absolute spatial variation in the firing rates of SA I nerve fibers. The dimension of dot clarity was strongly affected by adaptation of both the SA I channel and the PC channel. Adaptation of the PC channel increased dot clarity but adaptation of the SA I channel decreased it. This finding suggests that the perceived roughness of the microstructure of a textured surface is enhanced by the activity of the PC channel but decreased by the activity of the SA I channel.