The relationship between speech perception and electrode discrimination in cochlear implantees

Abstract

Speech Intelligibility Index (SII) procedures were used to measure the amount of speech information perceived in five frequency bands (170-570, 570-1170, 1170-1768, 1768-2680, and 2680-5744 Hz) by 15 users of the Cochlear Ltd. CI-22M implant and Spectra-22/SPEAK processor. The speech information perceived was compared to that perceived by normal-hearing listeners. The ability of these subjects to discriminate between stimulation on adjacent electrodes corresponding to each frequency band was also investigated, using a 4IFC procedure with random current level variations of between 0% and 60% of the dynamic range. Relative to normal-hearing listeners, speech information was, on average, significantly more reduced in the four frequency regions between 170 and 2680 Hz than in the region 2680-5744 Hz. There was a significant correlation between electrode discrimination ability (when the random level variation encompassed 20% or more of the dynamic range) and the amount of speech information perceived in the four frequency regions between 170 and 2680 Hz. There was no such correlation in the region 2680-5744 Hz, regardless of the extent of random level variation. These results indicate that speech information in the low to medium frequencies is more difficult for implantees to perceive, that this difficulty is correlated with the difficulty in discriminating electrode place in the presence of random loudness variations, and that fine spectral discrimination may be relatively more important in the vowel-formant regions than in higher frequency regions.

Auditory Neuropathy/Dys-synchrony and Its Perceptual Consequences

“…Furthermore, frequency resolution in cochlear implant patients (in this case the ability to distin-guish different electrode positions) has also been related to speech perception (Henry et al, 2000).…”

Trends in Cochlear Implants

“…Similarly in Mandarin-speaking cochlear-implant users, rate discrimination and tone recognition were significantly correlated (Wei et al, 1999). In the spectral domain, electrode discriminability and spectral resolvability were also found to be correlated with speech performance (Nelson et al, 1995;Henry et al, 2000;Henry and Turner, 2003). However, these correlation studies typically did not address the underlying processing mechanisms.…”

Spatial Selectivity to Intracochlear Electrical Stimulation in the Inferior Colliculus is Degraded After Long-Term Deafness in Cats

“…It is presumed that the activation of spatially restricted neural populations is essential for successful CI channel separation and thus for optimum speech discrimination performance in multichannel cochlear implant users (Chatterjee and Shannon 1998;Henry et al 2000;Townsend et al 1987;Throckmorton and Collins 1999;Zwolan et al 1997). To investigate the effects of long-term deafness on spatial selectivity, we determined the STC widths and dynamic ranges of ICC responses.…”

“…Psychophysical studies in human CI users have demonstrated that greater channel interaction is negatively correlated with the ability to rank the pitch of individual CI channels (Townsend et al 1987) and with speech discrimination performance (Chatterjee and Shannon 1998;Henry et al 2000;Throckmorton and Collins 1999;Zwolan et al 1997).…”