title: Sparse Nonnegative Matrix Factorization Strategy for Cochlear Implants.
abstract: Current cochlear implant (CI) strategies carry speech information via the waveform envelope in frequency subbands. CIs require efficient speech processing to maximize information transfer to the brain, especially in background noise, where the speech envelope is not robust to noise interference. In such conditions, the envelope, after decomposition into frequency bands, may be enhanced by sparse transformations, such as nonnegative matrix factorization (NMF). Here, a novel CI processing algorithm is described, which works by applying NMF to the envelope matrix (envelopogram) of 22 frequency channels in order to improve performance in noisy environments. It is evaluated for speech in eight-talker babble noise. The critical sparsity constraint parameter was first tuned using objective measures and then evaluated with subjective speech perception experiments for both normal hearing and CI subjects. Results from vocoder simulations with 10 normal hearing subjects showed that the algorithm significantly enhances speech intelligibility with the selected sparsity constraints. Results from eight CI subjects showed no significant overall improvement compared with the standard advanced combination encoder algorithm, but a trend toward improvement of word identification of about 10 percentage points at +15 dB signal-to-noise ratio (SNR) was observed in the eight CI subjects. Additionally, a considerable reduction of the spread of speech perception performance from 40% to 93% for advanced combination encoder to 80% to 100% for the suggested NMF coding strategy was observed.
authors.affiliation: Institute of Sound and Vibration Research, University of Southampton, UK Medizinische Physik, Universität Oldenburg and Cluster of Excellence "Hearing4all", Oldenburg, Germany hongmei.hu@uni-oldenburg.de.
authors.forename: Hongmei
authors.initials: H
authors.lastname: Hu
authors.affiliation: Institute of Sound and Vibration Research, University of Southampton, UK.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Lutman
authors.affiliation: Medizinische Physik, Universität Oldenburg and Cluster of Excellence "Hearing4all", Oldenburg, Germany.
authors.forename: Stephan D
authors.initials: SD
authors.lastname: Ewert
authors.affiliation: Institute of Sound and Vibration Research, University of Southampton, UK The Ear Institute, Faculty of Brain Sciences, University College London, UK.
authors.forename: Guoping
authors.initials: G
authors.lastname: Li
authors.affiliation: Institute of Sound and Vibration Research, University of Southampton, UK.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bleeck
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D019929:Cochlear Implantation / Q000379:methods; D003054:Cochlear Implants; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D012815:Signal Processing, Computer-Assisted; D059629:Signal-To-Noise Ratio; D013018:Sound Spectrography / Q000379:methods; D013067:Speech Perception / Q000502:physiology*; D049250:Speech Recognition Software
keywords: babble noise; cochlear implant; nonnegative matrix factorization; speech enhancement; speech recognition; vocoder