Does over-exposure modify the fine structure of distortion product otoacoustic emissions?

It is investigated, whether the pattern of distortion product otoacoustic emission (DPOAE) fine structure (quasi-periodic variations across frequency) is altered by an acoustical over-exposure. DPOAE fine structures are determined in 16 normal-hearing humans using a high frequency-resolution and primary levels of L1/L2=65/45 dB. DPOAEs are measured both before and after the subjects are monaurally exposed to a 1 kHz tone lasting for 3 min at an equivalent threshold sound pressure level of 105.5 dB. After the exposure the DPOAE levels are shifted to lower values and recover to the initial levels within 20 minutes. The DPOAE fine structure pattern is analyzed by an automatic classification algorithm, which determines ripple center frequency, ripple spacing, ripple height and ripple prevalence. For some individuals, an alteration of some of the parameters could be observed after the exposure, i.e. either a more pronounced or a less pronounced fine structure could be observed after the exposure. Across subjects, no shift of the fine structure pattern in frequency could be observed, also none of the calculated parameters changed consistently after the exposure. The results do not support the idea that the DPOAE fine structure might contain more information about the state of hearing than the DPOAE level.It is investigated, whether the pattern of distortion product otoacoustic emission (DPOAE) fine structure (quasi-periodic variations across frequency) is altered by an acoustical over-exposure. DPOAE fine structures are determined in 16 normal-hearing humans using a high frequency-resolution and primary levels of L1/L2=65/45 dB. DPOAEs are measured both before and after the subjects are monaurally exposed to a 1 kHz tone lasting for 3 min at an equivalent threshold sound pressure level of 105.5 dB. After the exposure the DPOAE levels are shifted to lower values and recover to the initial levels within 20 minutes. The DPOAE fine structure pattern is analyzed by an automatic classification algorithm, which determines ripple center frequency, ripple spacing, ripple height and ripple prevalence. For some individuals, an alteration of some of the parameters could be observed after the exposure, i.e. either a more pronounced or a less pronounced fine structure could be observed after the exposure. Across subjects, no shift of the fine structure pattern in frequency could be observed, also none of the calculated parameters changed consistently after the exposure. The results do not support the idea that the DPOAE fine structure might contain more information about the state of hearing than the DPOAE level