Some consideration on the auditory perception of ultrasound and its effects on hearing

It is well known that some auditory sensation is caused by ultrasound through bone conduction. In order to understand the mechanism of the perception of ultrasound and its effects on man, we investigated its pitch, loudness, temporary threshold shift and masking caused by ultrasound, including its threshold. Some interesting facts are found from these experiments. Namely, we can clearly perceive the pitch of ultrasound and it slightly varies with the frequency of stimulus, loudness level of ultrasound whose SPL is 2 dB above the threshold level becomes 60 phon, and recruitment appears in judgment of loudness. Moreover ultrasound can mask the sound in audio frequency range and TTS is observed in that range. From these results, we assume ultrasound is perceived by the vibration of around the basal end of basilar membrane and the distribution of excited position varies more or less with the ultrasonic frequency. And there exists a possibility that hearing damage will occur when we hear the ultrasound from some equipments or instruments.