Compound actionpotential tuning curves in normal and pathological human ears.

Abstract

Using a tone-on-tone masking procedure to just mask a compound actionpotential (AP) evoked by a 10 dB SL short toneburst yields frequency-intensity combinations for the tonal masker called AP tuning curves. This procedure is used in addition to the standard electrocochleography procedure to obtain information about the peripheral frequency selectivity. Both methods were performed on a (normal) group of patients having normal or nearly normal (within 15 dB) thresholds for frequencies above and including 1 kHz, and in patients having hearing losses of sensorineural origin exceeding 40 dB HL. In normal ears, the characteristic two-segment tuning curves are obtained. For pathological ears having a hearing loss of cochlear origin, tuning curves broadening by the loss of their sharp tips are obtained. There is some indication that in predominant neural hearing loss most of the sharp tuning is preserved. The changes in tuning associated with recovery from sudden deafness to almost normal hearing are reported. The overall conclusion is that the results obtained are in agreement with those from AP tuning curves reported in animal studies [P. Dallos and M.A. Cheatham, ’’Compound action potential (AP) tuning curves,’’ J. Acoust. Soc. Am. 59, 591–597 (1976)] as well as with changes in single-fiber tuning in reversible hearing loss [E. F. Evans, ’’Auditory frequency selectivity and the cochlear nerve,’’ in Facts and Models in Hearing, edited by E. Zwicker and E. Terhardt (Springer–Verlag, New York, 1974)].