Horizontal Localization of Sound Images and Sound Sources for Monaural Congenital Deafness

It is well known that the interaural time difference, interaural level difference and spectral cues are used to determine three-dimensional sound localization in binaural hearing. In the case of monaural hearing, the interaural time difference and interaural level difference are not used. Therefore, it is assumed that there is a different perception of sound localization between binaural and monaural hearing. In this study, we investigate the difference in the horizontal localization of sound images and sources in monaural hearing. An experiment involving horizontal sound localization was performed with one female participant suffering from congenital complete hearing loss in the left ear. The experimental system consisted of 12 loudspeakers placed horizontally on the circumference of a circle having a radius of 1 m at 30° intervals. Four experimental sessions were performed (including 60 white-noise stimuli per session). Excluding the instances with no localization (12%), all sound images were localized on the right side (0-180°). It appeared that sound images were localized on the side with the normal-hearing ear but not on the side with the deaf ear. Sound source localization was possible generally over 360° (with ± 30° allowance, 90.8%). As a result, we confirmed that the localization of sound images and sources was different in congenital monaural hearing.