Adaptive Recalibration of Chronic Auditory Gain

ABSTRACT

This report follows up and extends an exploratory investigation of a hypothetical adaptive chronic gain (amplification of suprathreshold information) process within the auditory system. In theory, this hypothetical gain process is plastic and can be systematically modified and recalibrated. The idea of an adaptive auditory gain mechanism is a fundamental concept in the treatment of both tinnitus and hyperacusis with tinnitus retraining therapy (TRT). This notion, however, has gone virtually untested. The hypothesis of this research is that judgments of loudness provide a functional index of chronic auditory gain. Further, chronic auditory gain can be manipulated either upward or downward in a controlled way by prolonged reduction or enhancement in the levels of background sound to which a listener is exposed. To evaluate these assertions, 8 normal-hearing volunteers were assigned randomly to continuous (23 hours/day), chronic (4-week) external sound treatments. Participants were exposed either to low-level sound produced by bilateral in-the-ear noise generators (NGs) or were fitted bilaterally with sound-attenuating earplugs (EPs) in a sequential crossover design. Both treatments produced elevated audibility thresholds, mainly above 1000 Hz. The effects of each treatment type on loudness judgments were evaluated to test the following predictions: (1) The EPs would enhance the magnitude of perceived loudness and the resulting loudness growth functions would become steeper as a consequence of chronic sound attenuation (consistent with enhanced system gain in response to diminished peripheral sound input); whereas, (2) the NGs would reduce the magnitude of perceived loudness and the resulting loudness growth functions would become shallower (consistent with diminished system gain in response to the elevated background input). Results after 4 weeks of each treatment were consistent with the above predictions, providing support for a plastic, chronic auditory gain process, and the use of sound therapy (i.e., NGs) in TRT.

KEYWORDS

Auditory gain - tinnitus retraining therapy - hyperacusis - loudness recalibration - sequential crossover trial

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