Vibratory Stimulation Transmission Pathways Measured by Subjective Threshold and DPOAE

Abstract

To clarify the skull content contribution to vibratory bone stimuli transmission and to determine stimuli features, we compared auditory threshold and distortion product otoacoustic emission (DPOAE) using a bone vibrator placed at different head sites, including the eye. The best audiometric threshold and the highest DPOAE were with the vibrator either on the mastoid of the measured side or on the temple’s “ultrasound window”. Auditory threshold with the bone vibrator on the eye resembled those of the forehead and were about 10 dB higher than at the best sites. DPOAEs were clearly present when air-conducted stimuli were presented through an inserted earphone and with the bone vibrator on the eye, indicating that vibratory sound is transmitted through skull content to the inner ear. The intracranial vibratory stimuli transmission pathway thus plays a significant role, particularly at low frequencies, and possibly also when vibratory stimuli are applied to the skull bone.