The benefit of cochlear-implant users’ head orientation to speech intelligibility in noise
Speech reception thresholds (SRTs) in noise improve when the speech and noise sources are spatially separated. This spatial release from masking (SRM) is usually investigated in fixed-head situations. We studied free-head situations in audio and audio-visual conditions. We compared normally- hearing and cochlear-implant (CI) users’ spontaneous and directed head- orientation strategies when attending to speech in noise with a progressively declining signal-to-noise ratio. SRM-model predictions suggested benefits of head orientation away from the target speech that we hypothesized would motivate head rotation. As signal-to-noise ratio declined, observed head tracks differed greatly between listeners. Audio-visual presentation reduced the amount of head rotation. When directed, listeners made more effective use of head rotation. Audio and audio-visual SRTs were acquired at fixed, 0, and 30 deg head orientations with respect to the target speech. At the most favourable 30-deg head orientation, SRM reached 8 and 6 dB for NH listeners and CI users respectively. Lip-reading yielded improvements of 3 and 5 dB on average across conditions. CI users confirmed that training in optimizing both their position and head orientation with respect to target speaker and noise source position in a social setting was both currently missing and likely valuable.
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