Abstract
CM and AP VDLs for continuous trains of clicks were recorded from guinea pigs having permanently fixed round-window membrane electrodes. The experimenter monitored oscilloscope-displayed evoked responses on line by manual adjustment of a motor driven recording attenuator. Békésy-audiometric-type graphical traces were obtained having at least 8-dB discrepancy (“amplitude” or envelope width) between descending and ascending VDLs. Comparable VDLs were also recorded photographically by making alternate down-up sweeps across nominal threshold level with no feedback control of the attenuator. Frame-by-frame analysis of the film was made off line by measuring stimulus pulse intensity associated with the disappearance (descending VDL) and reappearance (ascending VDL) of the evoked response. No significant overlap of descending and ascending thresholds was found using the photographic method. Statements in the audiologic literature postulating hypothetical auditory nerve processes underlying Békésy trace width are challenged. [Supported in part by NINDS.]
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