Preeti Rao
Robert Bilger
Dept. of Speech and Hear. Sci., Univ. of Illinois at Urbana--Champaign, 901 S. 6th St., Champaign, IL 61820
Auditory nonlinearities can give rise to an intermodulation distortion product at frequency=2f1-f2 from existing tones at f1 and f2. Such a phenomenon has been noted in ears with multiple spontaneous otoacoustic emissions (SOEs), where emissions are often observed at harmonically related frequencies [Burns et al., Hear. Res. 16, 271--278 (1984)]. SOEs, narrow-band signals with random amplitude, and phase fluctuations, are typically detected and estimated using the power spectrum. The power spectrum, however, suppresses all phase relations and cannot distinguish phase-coupled emissions from spontaneously excited ones. Cubically phase-coupled harmonics may be detected by the trispectrum [Swami and Mendel, IEEE Trans. ASSP 39, 1099--1109 (1991)]. Here, cubic differences tone SOEs are detected and the degree of phase coupling is quantified by a tricoherence index defined in terms of the power spectrum and an appropriately defined trispectrum of the input process. Data from the ears of subjects with multiple SOEs are analyzed for cubic coupling and the results are presented in the form of tricoherence spectra. [Work supported by DC00174.]