Summary A forward masking technique was used to measure cochlear gain reduction which might be consistent with the medial olivocochlear reflex (MOCR). A 4-kHz signal was set at 20 dB SL, and an on-frequency forward masker adjusted to just mask the signal. Adding a pink noise precursor before the signal and masker increased the level of the masker needed to mask the signal, in contrast to what would be expected from theories such as additivity of masking. The magnitude and pattern of this increase was similar to the increase in signal threshold seen with an off-frequency masker following a precursor.
There are psychoacoustic methods thought to measure gain reduction, which may be from the medial olivocochlear reflex (MOCR), a bilateral feedback loop that adjusts cochlear gain. Although studies have used ipsilateral and contralateral elicitors and have examined strength at different signal frequencies, these factors have not been examined within a single study. Therefore, basic questions about gain reduction, such as the relative strength of ipsilateral vs contralateral elicitation and the relative strength across signal frequency, are not known. In the current study, gain reduction from ipsilateral, contralateral, and bilateral elicitors was measured at 1-, 2-, and 4-kHz signal frequencies using forward masking paradigms at a range of elicitor levels in a repeated measures design. Ipsilateral and bilateral strengths were similar and significantly larger than contralateral strength across signal frequencies. Growth of gain reduction with precursor level tended to differ with signal frequency, although not significantly. Data from previous studies are considered in light of the results of this study. Behavioral results are also considered relative to anatomical and physiological data on the MOCR. These results indicate that, in humans, cochlear gain reduction is broad across frequencies and is robust for ipsilateral and bilateral elicitation but small for contralateral elicitation.
This is a continuation of a study examining the relationship between cochlear hearing loss and various psychoacoustic measures thought to be related to cochlear function. In the listeners tested, thresholds for long tones ranged from well within the clinically normal range to just outside this range. Where thresholds were elevated, other clinical tests were consistent with a cochlear origin. Because the medial olivocochlear reflex (MOCR) decreases the gain of the cochlear active process in response to sound, when possible, measures were made with short stimuli. Signal frequencies were 2, 4, and 8 kHz. Maximum gain was estimated by measuring the threshold masker level for a masker at the signal frequency and a masker well below the signal frequency. The effect of signal duration on threshold was measured using 10 and 200-signals. One point on the lower leg of the input/output function was measured by finding the threshold masker level for a masker slightly less than one octave below the signal frequency needed to mask a signal at 5 dB SL. Gain reduction was estimated by presenting a pink noise precursor before the signal and masker, and measuring the change in signal threshold as a function of precursor level. The relationship between these measures will be discussed. [Work supported by NIH(NIDCD)R01 DC008327 (EAS), and grants from the Purdue Office of the Executive Vice President for Research and the Purdue Graduate School (WS).]
This is a continuation of a study examining the relationship between cochlear hearing loss and psychoacoustic measures thought to be related to a cochlear function. In the listeners tested, audiometric thresholds for long tones ranged from well within the clinically normal range to just outside this range. Where thresholds were elevated, other clinical tests were consistent with a cochlear origin. Because the medial olivocochlear reflex decreases cochlear gain in response to sound, when possible, measures were made with short stimuli. Signal frequencies were from 1 to 8 kHz. One point on the lower leg of the input/output function was measured by finding threshold masker level for a masker almost one octave below the signal frequency needed to mask a signal at 5 dB SL. Gain reduction was estimated by presenting a pink broadband noise (BBN) precursor before the signal and masker and measuring the change in signal threshold as a function of the precursor level. Previous studies with listeners with normal hearing have shown that gain reduction begins at a low precursor level and grows compressively as the precursor level is increased. The current study is designed to determine whether this pattern changes when cochlear gain is permanently reduced. [Work supported by NIH(NIDCD)R01 DC008327 (EAS), the Purdue Office of the Executive Vice President for Research, and the Purdue Graduate School (WBS).]
This study examined the relationship between cochlear hearing loss and psychoacoustic measures related to cochlear function. Listeners’ audiometric thresholds for long tones ranged from well within the clinically normal range to just above this range. Where thresholds were elevated, other clinical tests were consistent with a cochlear origin. Because the medial olivocochlear reflex decreases cochlear gain in response to sound, measures were made with short stimuli. Signal frequencies were from 1 to 8 kHz. One point on the lower leg of the input/output function was measured by finding threshold masker level for a masker almost one octave below the signal frequency needed to mask a signal at 5 dB SL. Gain reduction was estimated by presenting a pink broadband noise precursor before the signal and masker and measuring the change in signal threshold as a function of precursor level. Previous studies with listeners with normal hearing have shown that gain reduction begins at a low precursor level and grows compressively as the precursor level is increased. In the present study, the estimate of gain reduction decreased as quiet threshold increased, but was not solely determined by the amount of gain. [Work supported by NIH(NIDCD)R01 DC008327 (EAS) and NIH(NIDCD) T32 DC016853 (WBS).]
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