Channel interaction limits melodic pitch perception in simulated cochlear implants

Abstract

In cochlear implants (CIs), melodic pitch perception is limited by the spectral resolution, which in turn is limited by the number of spectral channels as well as interactions between adjacent channels. This study investigated the effect of channel interaction on melodic contour identification (MCI) in normal-hearing subjects listening to novel 16-channel sinewave vocoders that simulated channel interaction in CI signal processing. MCI performance worsened as the degree of channel interaction increased. Although greater numbers of spectral channels may be beneficial to melodic pitch perception, the present data suggest that it is also important to improve independence among spectral channels.

The effect of spectral smearing on the identification of pureF0intonation contours in vocoder simulations of cochlear implants

“…Possible reliance on non-spectral cues might explain the effect of sharpening the noise filters from 20 to 40 dB/octave found by Litvak et al (2007) compared to the present study. The present results are also not in line with those of Crew et al (2012), who tested musical pitch contour discrimination using a tone (sine-wave) vocoder simulation. The stimuli were relatively similar to those of the current study, as they were controlled for duration and amplitude and a comparable number of bandpass filters were used (16).…”

“…Interaction between channels reduces the spectral detail of a signal ('spectral smearing') and, as a consequence, it compromises speech recognition performance (Crew et al, 2012;Henry and Turner, 2003). Previous studies have tested the effects of spectral smearing by varying the slope of the noise filters.…”

“…In order to control for the effects of confounding parameters on speech perception of CI users, vocoder simulations have been widely used with NH listeners (Dorman and Loizou, 1998;Shannon et al, 1995;Crew et al, 2012). Vocoders process speech in a manner comparable to the implant processor.…”

“…More recently, the effects of channel interaction were investigated in a non-speech pitch task. Crew et al (2012) used sinewave vocoder simulations with 16 bandpass filters and 3 filter slopes (24, 12, and 6 dB/octave) to test musical pitch perception. They replicated the findings of speech perception studies with steeper slopes producing more channel interaction and poorer performance in melodic contour identification.…”

Cochlear implant simulator with independent representation of the full spiral ganglion

“…However, Whitmal et al (2007) and Oxenham and Kreft (2014) argued that a tone vocoder may better reflect characteristics of electric hearing than a noise vocoder, because narrow-band noise carries intrinsic modulation that interferes with that of the speech envelope. Crew et al (2012) and Oxenham and Kreft (2014) proposed methods of incorporating current spread into tone-vocoded CI simulations. These schemes involve modulating the carriers by mixed envelopes, each carrier receiving a weighted contribution from the envelopes extracted at the analysis stage.…”