Thresholds to soft tissue conduction stimulation compared to bone conduction stimulation

This study was designed to compare the thresholds to a standard clinical bone vibrator applied to sites on the head over skull bone (bone conduction, BC) and to soft tissue sites on the head and neck (soft tissue conduction, STC) with static application forces of 100 and 500 g in order to assess the possibility that STC is actually a form of BC, since both are elicited by stimulation with the same bone vibrator. Thresholds to 2.0-kHz tones were assessed in dB hearing level settings of the audiometer in the BC stimulation mode. There was no difference in threshold between forces of 100 and 500 g when applied to the skull bone sites (e.g. mastoid, forehead). However, at soft tissue sites (e.g. below the ear lobe, under the chin, on the sterno-cleido-mastoid muscle), thresholds to 100 g were significantly higher (poorer) than those to 500 g. With the 500 g static force (and also with the 100 g force), the thresholds at the STC sites were higher (poorer) than those at the skull bone sites. These findings have implications for understanding BC and STC modes of auditory activation.