Auditory and vibrotactile interactions in perception of timbre acoustic features

Recently, there has been increasing interest in developing auditory-to-vibrotactile sensory devices. However, the potential of these technologies is constrained by our limited understanding of which features of complex sounds can be perceived through vibrations. The present study aimed to investigate the vibrotactile perception of acoustic features related to timbre, an essential component to identify environmental, speech and musical sounds. Discrimination thresholds were measured for six features: three spectral (number of harmonics, harmonic roll-off ratio, even-harmonic attenuation) and three temporal (attack time, amplitude modulation depth and amplitude modulation frequency) using auditory, vibrotactile and combined auditory + vibrotactile stimulation in 31 adult humans with normal tactile and auditory sensitivity. Result revealed that all spectral and temporal features can be reliably discriminated via vibrotactile stimulation only. However, for spectral features, vibrotactile thresholds were significantly higher (i.e., worse) than auditory thresholds whereas, for temporal features, only vibrotactile amplitude modulation frequency was significantly higher. With simultaneous auditory and tactile presentation, thresholds significantly improved for attack time and amplitude modulation depth, but not for any of the spectral acoustic features. These results suggest that vibrotactile temporal cues have a more straightforward potential for assisting auditory perception, while vibrotactile spectral cues may require specialized signal processing schemes.