Masked Tone Thresholds Are Related to Efferent-Induced Linearization of Human DPOAE I/O FunctionsAbstracts of the Annual MidWinter Research Meeting of the Association for Research in Otolaryngology (2016)
It is widely accepted that the living, healthy basilar membrane responds to increasing levels of acoustic input by compressing its mechanical output at certain locations across the cochlear partition. Basilar membrane (BM) input-output (I/O) functions at the characteristic frequency in mammalian animal models are characterized by two or three segments that are separated by transitions in response growth rate at the characteristic frequency. Stimulation of medial olivocochlear (MOC) efferent neurons reduces BM sensitivity and increases the slope of BM (I/O) functions in animal models. It has been postulated that MOC efferent neurons play a role in modifying cochlear output to improved detection of signals in noise. Increased linearity of I/O functions at CF associated with activation of MOC efferent neurons can conceivably assist in extending the neural response to the tone above that of noise, leading to an improvement in deteting tones in noise. To test this hypothesis, BM compression was studied indirectly in humans by measuring distortion-product otoacoustic emission (DPOAE) I/O functions in conditions with presentation of contralateral noise. Compression estimates from a threesegment linear regression model applied to the DPOAE functions were derived in order to determine associations with psychophysical measurements of masked tone thresholds. In masking conditions, the tone signal and the noise masker were presented at the same time and were directed to the right ear. Estimation of masked thresholds was provided by a twointerval, two-alternative forced-choice procedure with a twodown one-up adaptive rule. In this study, there were statistically significant associations between DPOAE I/O function slopes and masked thresholds at both 1.0 and 2.0 kHz. At 1.0 kHz, individuals with higher DPOAE I/O function slopes exhibited lower masked thresholds. In contrast to the results seen at 1.0 kHz, data at 2.0 kHz indicated that individuals with lower masked thresholds exhibited lower DPOAE I/O function slopes. When measured with contralateral noise, DPOAE I/O compression slopes were linked to masked thresholds at both frequencies examined in this study. Linearized DPOAE I/O functions presumably reflect linearized BM growth functions under conditions of MOC efferent activation, and this process may have extended the neural response to the signal tone in certain conditions so that it could be more easily heard in the presence of masking noise.
Citation InformationShaum P. Bhagat and Anusha Yellamsetty. "Masked Tone Thresholds Are Related to Efferent-Induced Linearization of Human DPOAE I/O Functions" Abstracts of the Annual MidWinter Research Meeting of the Association for Research in Otolaryngology Vol. 39 (2016) p. 402 - 402
Available at: http://works.bepress.com/shaum-bhagat/81/