Harmonicity of Sound Alters Roughness Perception

Multisensory integration refers to the integration of multiple senses by the nervous system. Auditory andtactile features are closely related senses as can be understood from the fact that adjectives such as soft,rough, and warm are used commonly for auditory and tactile features. Previous studies show that auditorycues play an important role to assess the roughness of a surface. Different characteristics of auditory cuessuch as amplitude and frequency may cause perceiving surface rougher or smoother. In this study, weinvestigate the effects of harmonic and inharmonic sounds on roughness perception to examine whetherauditory roughness will affect the tactile roughness perception while they are presented simultaneously.We expected the participants to perceive surfaces rougher while they listen to inharmonic sounds due toauditory roughness. We presented simultaneous and sequential harmonic and inharmonic sounds withthree sandpapers with different roughness levels (P100, P120, P 150 grit numbers) to the participants. Wefound that participants perceive sandpaper with the P120 grit number rougher while they listen tosimultaneous inharmonic sounds than simultaneous harmonic sounds. However, any effect of harmonicityon the sandpapers with P100 and P150 grit numbers was not observed. We suggest that auditoryroughness may enhance tactile roughness perception for surfaces with particular roughness levels,possibly when the roughness estimation from the tactile sense remains ambiguous.

Tactile perception of the roughness of 3D-printed textures

Surface roughness is one of the most important qualities in haptic perception. Roughness is a major identifier for judgments of material composition, comfort, and friction and is tied closely to manual dexterity. Some attention has been given to the study of roughness perception in the past, but it has typically focused on noncontrollable natural materials or on a narrow range of artificial materials. The advent of high-resolution three-dimensional (3D) printing technology provides the ability to fabricate arbitrary 3D textures with precise surface geometry to be used in tactile studies. We used parametric modeling and 3D printing to manufacture a set of textured plates with defined element spacing, shape, and arrangement. Using active touch and two-alternative forced-choice protocols, we investigated the contributions of these surface parameters to roughness perception in human subjects. Results indicate that large spatial periods produce higher estimations of roughness (with Weber fraction = 0.19), small texture elements are perceived as rougher than large texture elements of the same wavelength, perceptual differences exist between textures with the same spacing but different arrangements, and roughness equivalencies exist between textures differing along different parameters. We posit that papillary ridges serve as tactile processing units, and neural ensembles encode the spatial profiles of the texture contact area to produce roughness estimates. The stimuli and the manufacturing process may be used in further studies of tactile roughness perception and in related neurophysiological applications. NEW & NOTEWORTHY Surface roughness is an integral quality of texture perception. We manufactured textures using high-resolution 3D printing, which allows precise specification of the surface spatial topography. In human psychophysical experiments we investigated the contributions of specific surface parameters to roughness perception. We found that textures with large spatial periods, small texture elements, and irregular, isotropic arrangements elicit the highest estimations of roughness. We propose that roughness correlates inversely with the total contacted surface area.