Spectral contrast enhancement improves speech intelligibility in noise for cochlear implants

Abstract

Spectral smearing causes, at least partially, that cochlear implant (CI) users require a higher signal-to-noise ratio to obtain the same speech intelligibility as normal hearing listeners. A spectral contrast enhancement (SCE) algorithm has been designed and evaluated as an additional feature for a standard CI strategy. The algorithm keeps the most prominent peaks within a speech signal constant while attenuating valleys in the spectrum. The goal is to partly compensate for the spectral smearing produced by the limited number of stimulation electrodes and the overlap of electrical fields produced in CIs. Twelve CI users were tested for their speech reception threshold (SRT) using the standard CI coding strategy with and without SCE. No significant differences in SRT were observed between conditions. However, an analysis of the electrical stimulation patterns shows a reduction in stimulation current when using SCE. In a second evaluation, 12 CI users were tested in a similar configuration of the SCE strategy with the stimulation being balanced between the SCE and the non-SCE variants such that the loudness perception delivered by the strategies was the same. Results show a significant improvement in SRT of 0.57 dB (p < 0.0005) for the SCE algorithm.

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

“…The amount of spectral contrast enhancement can be controlled by a single parameter termed SCE factor. A more detailed description of the algorithm will be published elsewhere (Nogueira et al 2016). …”

“…The baseline or reference speech coding strategy is the advanced combinational encoder (ACE, a description of this strategy can be found in Nogueira et al 2005). The ACE strategy can be summarized in five signal processing blocks: (1) The Fast Fourier Transform (FFT); (2) The envelope detector; (3) The NofM band selection; (4) The loudness growth function (LGF) compression and (5) The channel mapping.…”

Piecewise-Linear Frequency Shifting Algorithm for Frequency Resolution Enhancement in Digital Hearing Aids

“…The Spectral Contrast Enhancement (SCE) algorithm is proposed which enhances the spectrum of the original speech signal by increasing the amplitude difference while maintaining the original sound pressure level. Previous experimental results [8,9] showed that a certain degree of improvement was provided by this method in speech recognition.…”

“…Using this method, the frequency difference between the signal components is widened, and the aforementioned frequency confusion is alleviated. In previous studies [8,9], the cause and effect of frequency resolution decrease has been considered. It has been shown that when the response curve of the cochlear filter is widened, the peak-valley difference of the spectrum is decreased, which makes it difficult to perceive the formants of the speech.…”

Optimization of a Spectral Contrast Enhancement Algorithm for Cochlear Implants Based on a Vowel Identification Model

“…The baseline or reference speech coding strategy is the advanced combinational encoder (ACE, a description of this strategy can be found in Nogueira et al 2005).…”