A channel-selection criterion for suppressing reverberation in cochlear implants

• Published in: The Journal of the Acoustical Society of America Vol. 129; no. 5; pp. 3221 - 3232
• Main Authors: Kokkinakis, Kostas, Hazrati, Oldooz, Loizou, Philipos C.
• Format: Journal Article
• Language: English
• Published: Melville, NY Acoustical Society of America 01.05.2011; American Institute of Physics
• Subjects: Aged; Algorithms; Biological and medical sciences; Cochlear Implants; Cochlear Implants - standards; Diseases of the ear; Ent and stomatology; Equipment Design; Female; Hearing Loss, Sensorineural - physiopathology; Hearing Loss, Sensorineural - psychology; Hearing Loss, Sensorineural - surgery; Humans; Intelligibility; Male; Medical sciences; Middle Aged; Perceptual Distortion; Phonetics; Psychological Acoustics; Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects); Reverberation; Speech Acoustics; Speech Intelligibility; Speech Perception; Time Factors; Cochlea; Hearing aids; Auditive prosthesis; Inner ear
• ISSN: 0001-4966; 1520-8524; 1520-9024; 1520-8524
• DOI: 10.1121/1.3559683

Little is known about the extent to which reverberation affects speech intelligibility by cochlear implant (CI) listeners. Experiment 1 assessed CI users' performance using Institute of Electrical and Electronics Engineers (IEEE) sentences corrupted with varying degrees of reverberation. Reverberation times of 0.30, 0.60, 0.80, and 1.0 s were used. Results indicated that for all subjects tested, speech intelligibility decreased exponentially with an increase in reverberation time. A decaying-exponential model provided an excellent fit to the data. Experiment 2 evaluated (offline) a speech coding strategy for reverberation suppression using a channel-selection criterion based on the signal-to-reverberant ratio (SRR) of individual frequency channels. The SRR reflects implicitly the ratio of the energies of the signal originating from the early (and direct) reflections and the signal originating from the late reflections. Channels with SRR larger than a preset threshold were selected, while channels with SRR smaller than the threshold were zeroed out. Results in a highly reverberant scenario indicated that the proposed strategy led to substantial gains (over 60 percentage points) in speech intelligibility over the subjects' daily strategy. Further analysis indicated that the proposed channel-selection criterion reduces the temporal envelope smearing effects introduced by reverberation and also diminishes the self-masking effects responsible for flattened formants.