ASA 125th Meeting Ottawa 1993 May

3aPP8. The quadratic property of the human auditory sensation induced by focused amplitude-modulated ultrasound.

Shengke Zeng

Richard B. Beard

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

Three modes of low-intensity ((less than or equal to)100 mW/cm[sup 2]) monotone amplitude-modulated (AM) ultrasound are focused on the region of the human cochlear and the human auditory response patterns are observed. The AM ultrasonic signal is defined as f(t) cos (omega)t, where f(t) is the monotone modulation signal and (omega) is the angular frequency of the ultrasonic carrier. The three modes of f(t) cos (omega)t are: (1) carrier-suppressed AM mode, cos (Omega)t cos (omega)t; (2) square-rooted AM mode, (1+cos (Omega)t)[sup 1/2] cos (omega)t; (3) standard AM mode, (1+cos (Omega)t) cos (omega)t, where (Omega) is the angular frequency of the monotone. They are applied in sequence to stimulate the subject. The pattern of auditory sensation of the subject to the ultrasonic stimulations follows the square of the modulation signal, f[sup 2](t), which are: (1) cos[sup 2] (Omega)t; (2) [(1+cos (Omega)t)[sup 1/2]][sup 2]; (3) (1+cos (Omega)t)[sup 2]. The subject senses the pure tone of 2(Omega) for the first mode of the ultrasonic stimulation, the pure tone of (Omega) for the second mode of the ultrasonic stimulation, and the mixed tones of (Omega) with relatively weaker intensity of 2(Omega) for the third mode of the ultrasonic stimulation. The response patterns reveal that the AM ultrasound induced human auditory sensation has the property of f[sup 2](t). This quadratic property is similar to the parametric demodulation of the focused AM ultrasound in water which has the form of d/dt[f[sup 2](t)], (B>>1) [Novikov, Nonlinear Underwater Acoustics (Acoustical Society of America, Woodbury, NY, 1987), pp. 86--95]. [Work partially supported by Electro-Stim Corp.]