PERCEPTION OF SPEECH IN REVERBERANT CONDITIONS USING AM-FM COCHLEAR IMPLANT SIMULATION

Drgas, S, Blaszak, M.A.

Adam Mickiewicz University, Faculty of Physics, Institute of Acoustics, Poznan, Poland.

Purpose: This study assessed the effects of stimulus misidentification and cognitive processing errors in normal-hearing adults exposed to degraded auditory input simulating signals provided by cochlear implants in reverberation conditions.

Method: Under control were three variables: number of vocoder bands (6 and 12), instantaneous frequency change rate (none, 50, 400 Hz), and enclosures (different reverberation conditions). The analyses were made on the basis of: (a) nonsense words’ recognition scores for eight young normal-hearing listeners, (b) ease of listening based on the time of response (response delay), and (c) the subjective measure of difficulty (ten-degree scale).

Results: The maximum value of speech intelligibility in cochlear implant simulation for considered parameters was 70% and was obtained for non-reverberant conditions with 12-channel vocoder and changes of instantaneous frequency limited to 400 Hz. In the presence of reflections stimulus misidentification was about 10–20 percentage points higher. There was little difference between the 50 and 400 frequency modulation cutoff for 12-channel vocoder; however, in the case of 6 channels this difference was more significant.

Conclusions: Speech perception of cochlear implant users is extremely affected by the reverberation, especially in terms of subjective measures of listening difficulty. The 12-channel processing systems were shown to be more largely resistant to the tested levels of reverberation than 6-channel vocoder.

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