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Auditory neurophysiology.

Work in our laboratory focuses on auditory stimulus coding and neural information processing in the cochlea and auditory nerve. Research planned or in progress deals with: (1) neural mechanisms underlying performance on auditory perceptual tasks, (2) coding of electrical stimuli presented through cochlear prostheses, (3) computer models of auditory nerve activity in normal and impaired ears, and (4) cochlear excitation as it relates to micromechanical forces provided by outer hair cells (i.e., the "cochlear amplifier"). Most experiments involve single-cell recordings of activity in primary and second-order auditory neurons.  

The accompanying figure provides an example of the type of work we do. The acoustic spectrum of the vowel /eh/ is shown on the left. Predicted responses of every tenth fiber in the normal cat auditory nerve to that sound presented at low and moderately high intensities are shown in the middle panel. At the right are shown predicted responses of the same fibers to the same sound, but after the ear has been impaired by removing the mechanical influences of outer hair cells. Each activity pattern is plotted as a function of the frequency to which a fiber is most sensitive, and each dot corresponds to the discharge rate elicited in one fiber.  

In the normal ear the shape of the vowel spectrum is transmitted relatively faithfully in the spatial activity pattern at low intensities, but spatial specificity is lost at high intensities. This suggests that low-intensity vowels require a different mechanism for extracting spectral information. In contrast, the impaired ear does not respond to all /eh/ at low intensities, and the spatial activity pattern obtained at high intensities differs from that observed in normal hearing. Data such as these are useful in evaluating neural mechanisms for auditory stimulus coding and in determining the effects of hearing loss on perceptual processing.