Is fine structure in hearing threshold an indicator of a highly sensitive cochlea? Investigations on amplitude modulation detection

摘要

Pure-tone thresholds in normal hearing listeners often show quasiperiodic fluctuations of up to 15 dB over a frequency range of typically one-tenth of an octave. There are several indications from literature that this fine structure in hearing threshold (HTFS) might be an indicator of a healthy ear because of its high vulnerability to noise and ototoxic agents. If HTFS indicates a healthy cochlea the question arises to which extent the underlying cochlear mechanisms of fine structure may help to improve the overall performance of the auditory system near threshold. For pure tone detection this is certainly the case for the minima in HTFS. The current study investigates to which extent another capability of the auditory system supports the idea of a higher cochlear sensitivity in regions with hearing threshold fine structure. Amplitude modulation detection thresholds (MDTs) were measured in subjects with and without fine structure. For carrier levels below 25 dB HL it was found that subjects with HTFS show higher MDTs at threshold minima in comparison to their MDTs at threshold maxima as well as compared to the MDTs of subjects without HTFS. In other words cochlear places that are highly sensitive to pure tone detection show a relatively poor sensitivity to amplitude modulation detection.