Hearing-loss filter broadening preserves envelope statistics but CI current spread does not.

Evidence

One remaining question is whether HI listeners exhibit the same loss of sensitivity to inherent noise fluctuations as CI users. If so, the finding may go some way to explaining why both HI and CI populations exhibit less masking release than NH listeners when additional slow fluctuations are imposed on noise maskers (e.g., Festen and Plomp 1990 ; Nelson and Jin 2004 ; Stickney et al. 2004 ; Gregan et al. 2013 ). On one hand, cochlear hearing loss is generally accompanied by a loss of frequency selectivity, due to loss of function of the outer hair cells; on the other hand this “smearing” of the spectrum occurs before extraction of the temporal envelope, rather than afterwards, as is the case with CI processing. Because the smearing is due to wider filters, rather than envelope summation, the resultant envelopes from broader filters still have Rayleigh-distributed envelopes with the same overall relative modulation power as the envelopes from narrower filters (i.e., the same area under the modulation power spectrum, normalized to DC; see Fig. 1 ). In contrast, with CIs, the envelopes derived from summing the envelope currents from adjacent electrodes are no longer Rayleigh distributed and have lower modulation power, relative to the overall (DC) power in the envelope (Hu and Beaulieu 2005 ). — Dijk, Pim van, Physiology, Psychoacoustics and…, 2167