### ASA 125th Meeting Ottawa 1993 May

## 3aPP9. The effect of the square-root preconditioning on
amplitude-modulated ultrasonic hearing.

**Shengke Zeng
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Richard B. Beard
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*Biomed. Eng. and Sci. Inst., Drexel Univ., Philadelphia, PA 19104
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The discovery of the quadratic property of the human auditory sensation
induced by the focused amplitude-modulated (AM) ultrasound ( Zeng and Beard,
``The quadratic property of the human auditory sensation induced by focused
amplitude-modulated ultrasound,'' preceding abstract, this meeting) suggests
the need for preconditioning of the AM ultrasound stimuli. The preconditioning
can cancel the harmonic distortion which is caused by the quadratic effect in
ultrasonic hearing. This quadratic harmonic distortion slopes from about -3 dB
at 250 Hz (modulation frequency) to -11 dB at 2 kHz (modulation frequency). The
preconditioned AM ultrasound is in the form of [radical |f(t)[inf
min]|+f(t)[radical cos (omega)t, where f(t) is the modulation signal and
(omega) the angular frequency of the carrier. The non-negative of |f(t)[sub
min]|+f(t) guarantees that its square root can always be obtained. The auditory
perception to the preconditioned AM ultrasound is in the form of the square of
the modulation signal, |f(t)[sub min]|+f(t), which eliminates the harmonic
distortion. In auditory perception test, the ultrasound which is modulated by
the preconditioned and unconditioned consonant--vowel--consonant (CVC)
syllables is used to stimulate the human cochlea. The subject's preconditioned
ultrasonic intensity thresholds for CVC syllable recognition are lower than the
unconditioned ultrasonic intensity thresholds for the same CVC syllable
recognition. [Work partially supported by Electro-Stim Corp.]