Increasing spectral contrast enhancement worsens vowel identification in CI users

Evidence

In five CI users the new algorithm has been evaluated using a SMT task and a vowel identification task. The tasks were performed for SCE factors of 0 (no enhancement), 2 and 4. In general it seems that increasing the SCE factor produces a decrease in performance in both the SMT threshold and vowel identification. — Dijk, Pim van, Physiology, Psychoacoustics and…, 1821

A new sound coding strategy that enhances spectral contrast has been designed. The amount of spectral contrast enhancement can be controlled by a single parameter termed SCE factor. A model of vowel identification has been used to investigate the effect of SCE on vowel identification. The model predicts that increasing the amount of SCE increases vowel identification accuracy. Based on these results we decided to use SCE factors 2 and 4 (equivalent to increasing the original spectral contrast of the spectrum by 3 and by 5 in a dB scale). The new SCE strategy has been evaluated in CI users. Results from a vowel identification task and a SMT task in five CI users show differences in vowel identification scores for different SCE factors. In general, it seems that SCE produces a detrimental effect in spectral modulation detection and vowel identification in CI users. These results are contrary to the model predictions. Previous studies in the literature give reasons to believe that spectral contrast enhancement would result in a benefit for the chosen tasks. It is possible that spectral valleys are attenuated too much and relevant information required by the CI users to understand speech is lost. These effects are not taken into account by the MPI model, and this could explain the contradictory results between experiments and CI users and modelling results. Still, it is possible that the SCE factors selected where too high, for this reason we think that a follow-up study should investigate whether lower amounts SCE can provide improvements in CI users. — Dijk, Pim van, Physiology, Psychoacoustics and…, 1886

Categorization

• QUESTION: Counter to the hypothesis that stronger spectral enhancement would help, it hurt. Why — over-emphasis distorting formant structure, or limited electrode resolution?
• XREF: Connects to the reader’s work on spectral envelope perception and the distinction between peaks and valleys in speech — likely echoes material in van Dijk chapters on spectral integration and modulation detection limits.
• corroborated: 3 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 1821; Dijk, Pim van, Physiology, Psychoacoustics and…, 1886