The ability to use binaural cues when stimulation was by bilaterally applied bone conduction (BC) transducers was investigated in 20 normal hearing participants. The results with BC stimulation were compared with normal air conduction (AC) stimulation through earphones. The binaural hearing ability was tested by spatial release from masking, binaural intelligibility level difference (BILD), binaural masking level difference (BMLD) using chirp stimulation, and test of the precedence effect. In all tests, the participants revealed a benefit of bilateral BC stimulation indicating use of binaural cues. In the speech based tests, the binaural benefit for BC stimulation was approximately half that with AC stimulation. For the BC BMLD test with chirp stimulation, there were indications of superposition of the ipsilateral and contralateral pathways at the cochlear level affecting the results. The precedence effect test indicated significantly worse results for BC stimulation than for AC stimulation with low-frequency stimulation while they were close for high-frequency stimulation; broad-band stimulation gave results that were slightly worse than the high-frequency results

The results confirm that binaural hearing processing with bilateral BC stimulation at the mastoid position is also present at the BCHA implant position. This indicates the ability for binaural hearing in patients with good cochlear function when using bilateral BCHAs.

Loudness functions with air and bone conduction stimulation in normal-hearing subjects using a categorical loudness scaling procedure, 2013, Hearing Research, (301) AbstractIn a previous study (Stenfelt et al., 2002) a loudness balance test between bone conducted (BC) sound and air conducted (AC) sound was performed at frequencies between 0.25 and 4 kHz and at levels corresponding to 30 to 80 dB HL. The main outcome of that study was that for maintaining equal loudness, the level increase of sound with BC stimulation was less than that of AC stimulation with a ratio between 0.8 and 0.93 dB/dB. However, because it was shown that AC and BC tone cancellation was independent of the stimulation level, the loudness level difference did not originate in differences in basilar membrane stimulation. Therefore, it was speculated that the result could be due to the loudness estimation procedure. To investigate this further, another loudness estimation method (adaptive categorical loudness scaling) was here employed in 20 normal-hearing subjects.The loudness of a low-frequency and a high-frequency noise burst was estimated using the adaptive categorical loudness scaling technique when the stimulation was bilaterally by AC or BC. The sounds where rated on an 11-point scale between inaudible and too loud. The total dynamic range for these sounds was over 80 dB when presented by AC (between inaudible and too loud) and the loudness functions were similar for the low and the high-frequency stimulation. When the stimulation was by BC the loudness functions were steeper and the ratios between the slopes of the AC and BC loudness functions were 0.88 for the low-frequency sound and 0.92 for the high-frequency sound.These results were almost equal to the previous published results using the equal loudness estimation procedure, and it was unlikely that the outcome stems from the loudness estimation procedure itself. One possible mechanism for the result was loudness integration of multi-sensory input. However, no conclusive evidence for such a mechanism could be given by the present study.Keywords: Bone conduction, loudness, categorical loudness scaling, multi-sensory integration.3 Highlights• The loudness function was steeper when stimulation was by BC than by AC• The difference between the loudness function slopes was greatest at low frequencies• The average ratios between AC and BC loudness function slopes were between 0.88 and 0.92• The difference between the AC and BC loudness functions were found at both low and high intensities.