Psychophysical and speech perception studies: A case report on a binaural cochlear implant subject

Abstract

Further improvements in speech perception for cochlear implant patients in quiet and in noise should be possible with speech processing strategies using binaural implants. For this reason, presented here is a series of initial psychophysical and speech perception studies on the authors' first binaural cochlear implant patient. For an approximate matching of the places of stimulation on the two sides, the patient usually reported a single percept when the two sides were simultaneously stimulated. Lateralization was strongly influenced by amplitude differences between the electrical stimuli on the two sides, but only weakly by interaural time delays. Speech testing, comparing monaural with binaural electrical stimulation, showed a binaural advantage particularly in noise.

Abnormal Binaural Spectral Integration in Cochlear Implant Users

“…requires the binaural cues such as interaural level and timing differences to be incorporated into a single auditory image with a single location. In the simple case of a single sound source, abnormally broad fusion will still allow successful localization with stimuli that are mismatched in cochlear place or frequency between ears (e.g., van Hoesel et al,1993). However, in the presence of multiple sound sources (such as in a cocktail party), abnormally broad fusion is more likely to lead to interference in localization as well as speech perception.…”

“…In these studies, fusion of sounds across ears is an important prerequisite for being able to lateralize sounds, and lateralization is only measured for electrode pairs that are fused as a single auditory image. Thus, while not directly reported, it can be inferred from the electrode pairs studied that the fusion ranges are similarly abnormally wide in bilateral CI users, with a single electrode in one ear fusing with 6-15 electrodes in the other ear in a few case studies (van Hoesel et al 1993;van Hoesel and Clark 1997;Long et al 2003); this corresponds to fusion over 4-20 mm differences in cochlear locations of stimulation between ears, on a scale of octaves. Thus, the wide fusion ranges seen in bimodal CI users in this study are consistent with the wide fusion ranges seen in case studies of bilateral CI users.…”

Effect of age at onset of deafness on binaural sensitivity in electric hearing in humans

“…Previous experiments with electrical pulse-trains applied to electrode pairs, in which implant users were required to detect changes in ITD, have reported that discrimination thresholds for stimuli presented at low rates of about 100 Hz can be as low as 50-200 s in some patients but are up to an order of magnitude larger in others ͑van Hoesel et al, 1993;Lawson et al, 1998;Majdak et al, 2006;van Hoesel, 2007͒. Thresholds from best-performers in the cochlear implant population overlap with thresholds seen in moderately trained normal-hearing people ͑ϳ70 s͒ presented with low-frequency tones carrying ITD information ͑Blauert, 1997; Bernstein, 2001;Wright and Zhang, 2006͒. Our work differs from prior studies in a number of ways. First, rather than testing discrimination abilities for stimuli presented to the right vs left, binaural parameters that are associated with a range of locations in space in acoustic hearing were used in a lateralization task in which listeners reported a perceived intracranial position of the sound source for various ITD or ILD values.…”

MED-EL Cochlear Implants: State of the Art and a Glimpse Into the Future

“…32 Thus, prior to 1995, bilateral cochlear implantation was mainly not intended as a treatment for restoring binaural hearing abilities. In tests on these early patients, [32][33][34][35] it was nonetheless found that the auditory system has the potential to integrate information provided by 2 different devices. However, apart from Balkany et al 33 and van Hoesel et al, 35 no improvement in speech understanding had been reported.…”