Comodulation masking release in speech identification with real and simulated cochlear-implant hearing

Abstract

For normal-hearing (NH) listeners, masker energy outside the spectral region of a target signal can improve target detection and identification, a phenomenon referred to as comodulation masking release (CMR). This study examined whether, for cochlear implant (CI) listeners and for NH listeners presented with a "noise vocoded" CI simulation, speech identification in modulated noise is improved by a co-modulated flanking band. In Experiment 1, NH listeners identified noise-vocoded speech in a background of on-target noise with or without a flanking narrow band of noise outside the spectral region of the target. The on-target noise and flanker were either 16-Hz square-wave modulated with the same phase or were unmodulated; the speech was taken from a closed-set corpus. Performance was better in modulated than in unmodulated noise, and this difference was slightly greater when the comodulated flanker was present, consistent with a small CMR of about 1.7 dB for noise-vocoded speech. Experiment 2, which tested CI listeners using the same speech materials, found no advantage for modulated versus unmodulated maskers and no CMR. Thus although NH listeners can benefit from CMR even for speech signals with reduced spectro-temporal detail, no CMR was observed for CI users.

Comodulation Masking Release In Electric Hearing

“…Furthermore, the results of our previous studies in NH with vocoded stimuli (Pierzycki and Seeber 2010) suggest that improved encoding of the TFS information would be needed to provide additional cues for segregation of the signal from the masker. These limitations would add to the lack of benefit from comodulation and CMR for speech perception in noise in CI users (Ihlefeld et al 2012). …”

“…Thus CMR was based on within-channel cues. A more recent study investigated speech perception in noise under conditions of CMR with CIs (Ihlefeld et al 2012). No benefit to speech understanding from comodulation was found.…”

Developmental Conductive Hearing Loss Reduces Modulation Masking Release

“…Both MMR and MMR+ are strongly reduced in hearing-impaired individuals and cochlear-implant users ( Bacon, Opie, & Montoya, 1998 ; Ihlefeld, Shinn-Cunningham, & Carlyon, 2012 ; Léger, Reed, Desloge, Swaminathan, & Braida, 2015 ; Nelson, Jin, Carney, & Nelson, 2003 ; Oxenham & Kreft, 2014 ; Pierzycki & Seeber, 2014 ; Zirn, Hempel, Schuster, & Hemmert, 2013 ). Although peripheral dysfunction can explain much of this impairment, MMR is thought to arise from a combination of peripheral and CNS mechanisms ( Christiansen & Oxenham, 2014 ; Dau, Ewert, & Oxenham, 2009 ; Dau, Piechowiak, & Ewert, 2013 ).…”

Brainstem Correlates of Comodulation Masking Release for Speech in Normal Hearing Adults

“…The masking release is reduced for the maskers with relatively flat spectrum, and a steady-state noise is likely to mask the lower level portions of speech. Other studies show that masking release and grouping mechanism are interrelated since the latter is likely to vanish in conditions such as loss of temporal fine-structure information (as seen in cochlear implant users) and reduced spectral resolution [ 5 ]. According to our findings, the brainstem encoding of temporal fine-structure information is an important factor in CMR, which might result in stream segregation, auditory grouping, and auditory object formation.…”

“…Moreover, the study develops the knowledge of the subcortical encoding of speech in noise. Additionally, the present study has potential to show that neural representation of the F0 and other components of speech in brainstem can be used as neural indexes of CMR in individuals with poor CMR (for example, hearing-impaired listeners [ 17 ], children [ 18 ], adults with auditory processing disorder [ 19 ] and cochlear implant users [ 5 ]). We also explore the role of brainstem processes in CMR by the auditory brainstem response to complex sounds (cABR).…”