Word Recognition and Frequency Selectivity in Cochlear Implant Simulation: Effect of Channel Interaction

Abstract

In cochlear implants (CI), spread of neural excitation may produce channel interaction. Channel interaction disturbs the spectral resolution and, among other factors, seems to impair speech recognition, especially in noise. In this study, two tests were performed with 20 adult normal-hearing (NH) subjects under different vocoded simulations. First, there was a measurement of word recognition in noise while varying the number of selected channels (4, 8, 12 or 16 maxima out of 20) and the degree of simulated channel interaction (“Low”, “Medium” and “High”). Then, there was an evaluation of spectral resolution function of the degree of simulated channel interaction, reflected by the sharpness (Q10dB) of psychophysical tuning curves (PTCs). The results showed a significant effect of the simulated channel interaction on word recognition but did not find an effect of the number of selected channels. The intelligibility decreased significantly for the highest degree of channel interaction. Similarly, the highest simulated channel interaction impaired significantly the Q10dB. Additionally, a strong intra-individual correlation between frequency selectivity and word recognition in noise was observed. Lastly, the individual changes in frequency selectivity were positively correlated with the changes in word recognition when the degree of interaction went from “Low” to “High”. To conclude, the degradation seen for the highest degree of channel interaction suggests a threshold effect on frequency selectivity and word recognition. The correlation between frequency selectivity and intelligibility in noise supports the hypothesis that PTCs Q10dB can account for word recognition in certain conditions. Moreover, the individual variations of performances observed among subjects suggest that channel interaction does not have the same effect on each individual. Finally, these results highlight the importance of taking into account subjects’ individuality and to evaluate channel interaction through the speech processor.

A Comparison of Montreal Cognitive Assessment Scores among Individuals with Normal Hearing and Cochlear Implants

“…HI individuals typically have poorer spectral resolution than NH individuals, but likely have better spectral resolution than CI recipients (e.g., Winn et al 2015), who are limited by electrical current spread and uneven neural survival patterns (e.g., Henry & Turner 2003; Hughes et al 2013; Swaddiwudhipong et al 2021). Broader current spread may be associated with more channel interaction and “blurring” of spectral peaks, thus causing spectral degradation (Henry & Turner 2003; Cucis et al 2021). It should be noted that speech perception was not measured for the CI recipients in the present study.…”

Effects of spectral smearing on speech understanding and masking release in simulated bilateral cochlear implants

“…frequency-to-place mismatch [ 15 ]). We acknowledge that some previous work on channel interaction has instead employed open-set lists [ 30 , 31 ].…”

L-type calcium channel blockade with verapamil prevents noise induced neuronal dys-synchrony

“…Therefore, synchronous activity would be disproportionately affected by calcium channel blockade in the inferior colliculus centrally, compared to the auditory periphery. While calcium channel blockade did not affect hearing thresholds, calcium channel blockade induced changes in central synaptic function can have effects on speech recognition and processing (Buschges et al, 2000;Choi et al, 2024;Cucis et al, 2021;Delaney & Crane, 2016;Ding & Vaziri, 1998;Friesen et al, 2001;Fu & Nogaki, 2005;Henry & Turner, 2003;Hildebrand et al, 2004;Ricoy & Frerking, 2014;Wheeler et al, 1994) This would suggest that use of calcium channel blockers for treatment of hypertension may generate undiagnosed synaptopathy. However, calcium channel blockade just prior to noise exposure, protected against noise-induced changes in neuronal synchrony.…”