Hero Wit

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Dissecting the frog inner ear with Gaussian noise. I. Application of high-order Wiener-kernel analysis

by Hero Wit and Pim Van Dijk

Hearing Research, 1997

Wiener kernel analysis was used to characterize the auditory pathway from tympanic membrane to si... more Wiener kernel analysis was used to characterize the auditory pathway from tympanic membrane to single primary auditory nerve fibers in the European edible frog, Rana esculenta. Nerve fiber signals were recorded in response to white Gaussian noise. By crosscorrelating the noise stimulus and the nerve fiber response, we computed (1) the full second-order Wiener kernel, and (2) the diagonals of the zeroth-to fourth-order Wiener kernels. These diagonals are usually referred to as polynomial correlation functions. The measured Wiener kernels were fitted with a 'sandwich' model. A new fitting procedure was used to compute the response characteristics of (1) the first filter, (2) the static nonlinearity, and (3) the second filter, which form the functional components of the model. The first filter is a bandpass filter. In the majority of low frequency fibers, with best excitatory frequency (BEF) < 800 Hz, this filter was tuned to two frequencies. This dual tuning mechanism gives rise to 'off-diagonal' components in the second-order Wiener kernel. The static nonlinearity resembles a rectifier, and is dominated by second-order (quadratic) nonlinearity. As a function of BEF, the shape of the nonlinearity changes systematically. Finally, the last filter in the model was a low pass filter. Across fibers, its cutoff frequency J-adB ranged from 106 to 434 Hz.

format_quoteThe second-order Wiener kernel showed tapered oscillations around 5 ms delays, indicating early response to stimuli.format_quote

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Are spontaneous otoacoustic emissions generated by self-sustained cochlear oscillators?

by Hero Wit and Glenis Long

The Journal of the Acoustical Society of America, 1991

Theoretical analyses supporting the assumption that spontaneous otoacoustic emissions (SOAEs) can... more Theoretical analyses supporting the assumption that spontaneous otoacoustic emissions (SOAEs) can be described as self-sustained oscillations (requiring a power source) are reviewed and extended. Spectral and statistical properties of spontaneous otoacoustic emissions are examined and shown to be consistent with this assumption. Several alternative models of spontaneous emissions (noise-driven saturating memoryless nonlinearity, noise-driven nonlinear-stiffness oscillator) are examined. Although some of these models are able to produce the types of statistical distributions of amplitude and displacement similar to those observed in the experimental data, this similarity is destroyed upon narrow-band filtering. PACS numbers: 43.64.Jb, 43.64. Bt the source of some controversy and confusion (Wit, 1989; Furst, 1989; see also Sec. V of this paper).

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