Effect of Channel Interaction and Presentation Level on Speech Recognitionin Simulated Bilateral Cochlear Implants

Abstract

The present study used the acoustic simulation of bilateral cochlear implants to investigate the effect of presentation level (EXP 1) and channel interaction (EXP 2) on binaural summation benefit in speech recognition. Methods: The acoustic 6-channel processors were constructed, and the envelope of each band was used to modulate a sinusoid (EXP 1) or band-pass filtered white noise (EXP 2) with a frequency matching the center frequency of the carrier band. Presentation level was fixed for one ear and varied for the other. Channel interaction was simulated by altering filter slopes while keeping interaural spectral peaks matched in the carrier bands. Two separate groups of ten adult subjects with normal hearing participated in EXP 1 and EXP 2. Sentence recognition was measured with left ear alone, right ear alone, and both ears in quiet and in noise at +5 dB signal-to-noise ratio. Results: A significant binaural summation benefit occurs only in noise, regardless of interaural mismatch in channel interactions and presentation levels. Conclusions: Results suggest that factors other than channel interaction are important and that matching interaural loudness is an unimportant factor in binaural summation benefit in noise. For both EXP 1 and EXP 2, the data trend is indicative of speech information perceived in quiet being fully coded by the better performing ear alone, which leads to no binaural summation benefit. The results of current and future studies could have implications in programming of bilateral cochlear implant users.

Perceptual confusions for temporally smoothed envelope of consonants in normal hearing listeners

“…The use of the temporal envelope cues of speech, the output of the vocoder, has been studied for speech recognition the last 10 years. Most CI simulation studies with a vocoder have been focused on determining the optimal number of channels for speech perception [4,17], the effect of the tonotopic mismatch produced by differences in CI electrode insertion depth [11,[22][23][24], and the effect of the channel interaction on speech perception [25]. All these studies were administered with less understanding of the nature of the temporal envelope information processed in normal auditory system.…”