Influence of high-frequency audibility on the perceived distance of sounds

When listening in natural environments, normal-hearing (NH) listeners usually perceive sounds out- side their head, i.e., externalized. Sounds perceived inside the head are called internalized. Hearing- impaired (HI) listeners have been reported to externalize sounds less accurately than NH listeners. In a study by Boyd et al. (2012), the average externalization ratings of NH listeners dropped and matched those of HI listeners when the signals were lowpass-filtered at 6.5 kHz. This suggested that reduced high-frequency audibility might cause a reduced externalization in HI listeners. The present study aimed at clarifying whether the perceived distance of sounds in HI listeners differs from NH data as well and, if so, whether distance-rating performance improves when reduced audibility is compensated for by amplification. Individual binaural room impulse responses (BRIRs) were mea- sured for nine different loudspeaker distances. NH and HI listeners were asked to rate the perceived distance of processed speech samples in a MUSHRA-like test paradigm according to optical markers placed in the same workshop room where the BRIR measurements were performed. NH listeners rated the distance of unfiltered and lowpass-filtered speech, and HI listeners that of unfiltered speech and of speech amplified to compensate for their audibility loss. The results for NH listeners showed no systematic effect of lowpass-filtering the stimuli at 2 kHz or 6 kHz on distance ratings and the measured distance curves were much steeper than those found in the literature. Preliminary results for three HI listeners showed large inter-subject variability, but as a tendency, the distance rating seemed to vary with the energy content of the signal rather than the bandwidth, indicating that loudness might be a strong contributor to distance perception in HI listeners.