Measurements of vibration at the external auditory meatus and the upper limb in the living human body caused by distantly presented bone-conducted ultrasound

Abstract

In bone conduction, vibrators are usually pressed onto the mastoid process, however, bone-conducted ultrasound (BCU) presented to body parts distant from the head can also be perceived. To elucidate mechanisms of the distantly presented BCU perception, transmissions of BCU were investigated on living human bodies. First, vibration at the external auditory meatus were measured when 30 kHz BCU was presented to distal parts. Second, vibrations of the upper limb were measured at nine surface points lined up straight from the forearm to shoulder when 30 kHz BCU was presented to nearby the wrist. The results showed that prominent spectrum peaks corresponding to the stimulus-frequency were observed at all parts. The vibration tended to decrease depending on the distance between the stimulus and measurement points, however, some exceptions existed. Efficiency of the BCU transmission seems to vary depending on factors like shape of the body, acoustical properties of the tissue, and coupling of the vibrator and the skin.