ASA 126th Meeting Denver 1993 October 4-8

3aPP9. The roles of parametric demodulation, rectifying demodulation, and coherent demodulation in human amplitude-modulated ultrasonic hearing.

Shengke Zeng Richard B. Beard

Biomed. Eng. and Sci. Inst., Drexel Univ., Philadelphia, PA 19104

The frequency pattern of the human auditory sensation in response to amplitude-modulated (AM) ultrasonic stimulation is observed to be proportional to the frequency spectrum of the square of the modulation functions [Zeng and Beard, J. Acoust. Soc. Am. 93, 2332 (A) (1993)]. In contrast, the frequency pattern of rectifying demodulation is proportional to the frequency spectrum of the absolute values of the modulation functions; and the frequency pattern of coherent demodulation is the spectrum of the modulation functions. The distinct discrepancies in frequency patterns between the auditory sensation in human ultrasonic hearing and the above two physical demodulations indicate that rectifying demodulation and coherent demodulation are irrelevant to human ultrasonic hearing. When the human subject's cochlear region is stimulated by an AM ultrasonic mode (1+cos 2(pi)Ft)cos 2(pi)ft, the subject can sense the fundamental modulation frequency F and the weaker second harmonic 2F, where f is the carrier frequency. The amplitude ratio of the intensity threshold for sensing the first harmonic to that for sensing the second harmonic is 0.37 at F=1 kHz, 0.57 at 250 Hz, and 0.68 at 3 kHz. Compared with the same ratio in parametric demodulation, which is 0.9, and in the demodulation caused by the quadratic property, which is 0.25, parametric demodulation is considered to have a joint influence in conjunction with the quadratic property on human AM ultrasonic hearing [Zeng, Ph.D. dissertation, Drexel Univ. (1993)]. [Work partially supported by Electro-Stim Corp.]