LXV The Significance of Round-Window-Recorded Cochlear Potentials in Hearing: An Autocorrelated Study in the Cat

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Abstract
Measurements of cochlear microphonic and N1 responses were obtained through permanently implanted electrodes while concomitant tonal threshold measures between 0.5 and 16 kc were obtained by a conditioned-avoidance technique. After stable response levels to all measures were achieved, the cochlea was damaged by loud sound, then allowed to recover till new stable levels for the same measures were reached. Associated changes in auditory threshold and electrical potentials were compared to pre-exposure normal. Such comparisons showed: (1) Input-output functions of cochlear microphonic measured at the round window do not reflect cochlear changes more apically located than a very few millimeters. (2) Round-window-measured cochlear microphonics do reflect cochlear partition damage related to threshold losses within a few millimeters of the round window[long dash]14 kc to approximately 30 kc. (3) The general concepts for the shape of the cochlear microphonic input-output function, as advanced by Davis, Fernandez, Tasaki, Eldredge, and others, best explain the over-all results of these experiments. (4) The VIII nerve action potential response in the normal cat correlated best with auditory threshold at 4 and 8 kc, but with a latitude of at least [plus or minus] 20 db. (5) Post-trauma changes in the action potential were varied, but in general supported a basal turn origin for click-excited N1.