Cochlear implant spectral smearing flattens formant peaks needed for speech recognition

Evidence

In a recent study, the identification of spectrally smeared vowels and consonants was improved by spectral contrast enhancement (SCE) in a group of 166 normal hearing listeners (Alexander et al. 2011 ). Spectral contrast is defined as the level difference between peaks and valleys in the spectrum. In CIs, spectral contrast is degraded because of the limited number of stimulation electrodes and overlapping electric fields activating the nervous system through the bony structure of the cochlea. This might reduce the differences in amplitudes between peaks and valleys in the input making it more difficult to locate spectral dominance (i.e., formants) which provide crucial cues to speech intelligibility and instrument identification. — Dijk, Pim van, Physiology, Psychoacoustics and…, 1827

Categorization

• DEFINE: Defines spectral contrast as the level difference between spectral peaks and valleys, and links formant (spectral dominance) peaks to intelligibility.
• XREF: The degradation of peaks-through-broad-neural-activation mechanism parallels noise’s masking of signal peaks in the reader’s ear-science reading.
• corroborated: 2 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 1827