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.