Comodulation Masking Release provoked by direct electrical stimulation of auditory nerve fibers

Listeners with sensorineural hearing loss experience severe deficits when processing signals in modulated noise for both signal detection and speech understanding. An ability of the normal-hearing (NH) auditory system in this context is enhanced signal detection through centrally-mediated analysis of synchronous (comodulated) level fluctuations across-frequency. Such temporal characteristics exhibit many natural sounds, e.g. plosives. Comodulation masking release (CMR) illustrates across-frequency processing. This study focuses on CMR in cochlear-impaired listeners provided with a cochlear-implant (CI). Signal presentation was realized via direct stimulation with the nucleus implant communicator in 20 CI users. The mean CMR was 3.1 dB in CI users (p<0.05) and therefore much smaller than in NH (12 dB, p<0.01). CMR varied strongly with etiology: long-term sensorineural hearing loss with impact to the peripheral or central auditory pathway, like e.g. progressive hearing loss, led to small amounts of CMR. Whereas short-term sensorineural hearing loss, e.g. acute hearing loss or blast trauma, resulted in a considerable high CMR as have been found in vocoder simulations in NH. We assume that centrally mediated across-frequency processing in electric hearing depends on hearing loss history.