Temporal Cues Contribute to Tactile Perception of Roughness

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Abstract
Optimal perception of surface roughness requires lateral movement between skin and surface, suggesting the importance of temporal cues. The roughness of periodic gratings is affected by changing either inter-element spacing (groove width,G) or element width (ridge width,R). Peripheral neural responses to gratings depend quantitatively on a spatial variable,G, and a temporal variable, grating temporal frequency (Ft), with changes inRacting indirectly through concomitant changes inFt. We investigated, psychophysically, the contribution of temporal cues to human tactile perception of roughness, using gratings varying in eitherRorG. Gratings were scanned across the immobile fingerpad with controlled movement speed (S) and contact force. In one experiment, we found that roughness magnitude estimates depended on bothGandFt. In a second experiment, discrimination of the roughness of gratings varying in eitherRorGwas affected by manipulatingFt. Overall, the effect ofGon roughness judgments was much stronger than that ofFt, probably explaining why many previous studies using surfaces that varied only in inter-element spacing led to the conclusion that temporal factors play no role in roughness perception. However, the perceived roughness ofR-varying gratings was determined byFtand not spatial variables. Roughness judgments were influenced byGandFtin a manner entirely consistent with predicted afferent response rates. Thus perceived roughness, like peripheral afferent responses, depends in part on temporal variables.

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