Auditory psychophysical performance without a cochlea

Abstract

Auditory psychophysical performance has been measured using electrical stimulation of the remaining VIII nerve and of the cochlear nucleus in deaf patients. Psychophysical measures of temporal envelope processing show relatively unimpaired performance in these patients compared to normal hearing, and speech discrimination scores indicate that speech information relating to temporal envelopes can be effectively transmitted and received. This finding also indicates that the cochlea and VIII nerve may play relatively little role in the following tasks: detection of gaps, detection of modulation, recovery from adaptation, nonspectral pitch discrimination, and duration discrimination. Intensity perception is impaired with electrical stimulation: dynamic range of usable loudness is only 10 to 20 dB and intensity discrimination experiments indicate only 10 to 40 discriminable intensity levels. Frequency resolution is completely absent in electrical stimulation and can be only crudely reconstructed by multiple electrodes stimulating discrete neural segments. Psychophysical experiments on multiple electrodes indicate that patients can perceive and discriminate complex dynamic patterns of electrical activity changing in both stimulation frequency and electrode location. The combination of temporal envelope formation and the coarse “frequency” resolution provided by multiple electrodes is adequate to convey a surprising amount of speech information. [Work supported by NIH.]