Effects of source-to-listener distance and masking on perception of cochlear implant processed speech in reverberant rooms

Abstract

Two experiments examined the effects of source-to-listener distance ͑SLD͒ on sentence recognition in simulations of cochlear implant usage in noisy, reverberant rooms. Experiment 1 tested sentence recognition for three locations in the reverberant field of a small classroom ͑volume= 79.2 m 3 ͒. Subjects listened to sentences mixed with speech-spectrum noise that were processed with simulated reverberation followed by either vocoding ͑6, 12, or 24 spectral channels͒ or no further processing. Results indicated that changes in SLD within a small room produced only minor changes in recognition performance, a finding likely related to the listener remaining in the reverberant field. Experiment 2 tested sentence recognition for a simulated six-channel implant in a larger classroom ͑volume= 175.9 m 3 ͒ with varying levels of reverberation that could place the three listening locations in either the direct or reverberant field of the room. Results indicated that reducing SLD did improve performance, particularly when direct sound dominated the signal, but did not completely eliminate the effects of reverberation. Scores for both experiments were predicted accurately from speech transmission index values that modeled the effects of SLD, reverberation, and noise in terms of their effects on modulations of the speech envelope. Such models may prove to be a useful predictive tool for evaluating the quality of listening environments for cochlear implant users.

A channel-selection criterion for suppressing reverberation in cochlear implants

“…Only a few studies were reported, and those studies involved primarily vocoder simulations conducted with normal-hearing listeners. For instance, in the studies by Poissant et al (2006) and Whitmal and Poissant (2009), normal-hearing adult listeners were presented with reverberant stimuli processed into 6-24 channels using tone-excited vocoders. Percent correct recognition scores were found to be significantly worse when speech inside a reverberant field with RT 60 ¼ 0.7 s was vocoded using a small number of channels (Whitmal and Poissant, 2009).…”

“…For instance, in the studies by Poissant et al (2006) and Whitmal and Poissant (2009), normal-hearing adult listeners were presented with reverberant stimuli processed into 6-24 channels using tone-excited vocoders. Percent correct recognition scores were found to be significantly worse when speech inside a reverberant field with RT 60 ¼ 0.7 s was vocoded using a small number of channels (Whitmal and Poissant, 2009). The authors concluded that in all conditions tested, the reverberation time and the directto-reverberant ratio (DRR) 1 had a negative impact on the speech identification performance of the listeners.…”

Use of Amplitude Modulation Cues Recovered from Frequency Modulation for Cochlear Implant Users When Original Speech Cues Are Severely Degraded

“…Previous studies by Poissant et al (2006) and Whitmal and Poissant (2009) controlled the spectral resolution of normal-hearing listeners and showed a systematic degradation in speech identification as the number of vocoder channels decreased.…”

“…In general, if the space is surrounded by materials that are highly reflective (e.g., concrete, tile, wood flooring, bricks, and glass), RT 60 values are high. The effects of reverberation on speech identification for CI users has recently received extensive attention (e.g., Poissant et al 2006;Whitmal and Poissant 2009;Zheng et al 2011;Tillery et al 2012). In the present study, when the effect of reverberation was introduced, speech identification performance remained constant until RT 60 = 0.6, and then decreased significantly at RT 60 =1.0.…”

Análise do ruído e intervenção fonoaudiológica em ambiente escolar: rede privada e pública de ensino regular

“…The study of cochlear implant users revealed the difficulties these users have in understanding speech within the school environment, suggesting that such students should position themselves nearer the speaker (teacher) to help speech understanding 29 .…”