Browsing by Author "Francart, Tom"

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    Psychophysics, fitting, and signal processing for combined hearing aid and cochlear implant stimulation
    (Lippincott Williams & Wilkins, 2013-11) Francart, Tom; McDermott, Hugh
    The addition of acoustic stimulation to electric stimulation via a cochlear implant has been shown to be advantageous for speech perception in noise, sound quality, music perception, and sound source localization. However, the signal processing and fitting procedures of current cochlear implants and hearing aids were developed independently, precluding several potential advantages of bimodal stimulation, such as improved sound source localization and binaural unmasking of speech in noise. While there is a large and increasing population of implantees who use a hearing aid, there are currently no generally accepted fitting methods for this configuration. It is not practical to fit current commercial devices to achieve optimal binaural loudness balance or optimal binaural cue transmission for arbitrary signals and levels. There are several promising experimental signal processing systems specifically designed for bimodal stimulation. In this article, basic psychophysical studies with electric acoustic stimulation are reviewed, along with the current state of the art in fitting, and experimental signal processing techniques for electric acoustic stimulation.
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    Sound coding in cochlear implants: from electric pulses to hearing
    (IEEE, 2015-03) Wouters, Jan; McDermott, Hugh; Francart, Tom
    Cochlear implantation is a life-changing intervention for people with a severe hearing impairment [1]. For most cochlear implant (CI) users, speech intelligibility is satisfactory in quiet environments. Although modern CIs provide up to 22 stimulation channels, information transfer is still limited for the perception of fine spectrotemporal details in many types of sound. These details contribute to the perception of music and speech in common listening situations, such as where background noise is present. Over the past several decades, many different sound processing strategies have been developed to provide more details about acoustic signals to CI users. In this article, progress in sound coding for CIs is reviewed. Starting from a basic strategy, the current commercially most-used signal processing schemes are discussed, as well as recent developments in coding strategies that aim to improve auditory perception. This article focuses particularly on the stimulation strategies, which convert sound signals into patterns of nerve stimulation. The neurophysiological rationale behind some of these strategies is discussed and aspects of CI performance that require further improvement are identified
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    Speech perception and localisation with SCORE bimodal: A loudness normalisation strategy for combined cochlear implant and hearing aid stimulation
    (PLOS, 2012-10) Francart, Tom; McDermott, Hugh
    A significant fraction of newly implanted cochlear implant recipients use a hearing aid in their non-implanted ear. SCORE bimodal is a sound processing strategy developed for this configuration, aimed at normalising loudness perception and improving binaural loudness balance. Speech perception performance in quiet and noise and sound localisation ability of six bimodal listeners were measured with and without application of SCORE. Speech perception in quiet was measured either with only acoustic, only electric, or bimodal stimulation, at soft and normal conversational levels. For speech in quiet there was a significant improvement with application of SCORE. Speech perception in noise was measured for either steady-state noise, fluctuating noise, or a competing talker, at conversational levels with bimodal stimulation. For speech in noise there was no significant effect of application of SCORE. Modelling of interaural loudness differences in a long-term-average-speech-spectrum-weighted click train indicated that left-right discrimination of sound sources can improve with application of SCORE. As SCORE was found to leave speech perception unaffected or to improve it, it seems suitable for implementation in clinical devices.