Perception of speech, music and emotion by hearing-impaired listeners

The everyday tasks of perceiving speech, music and emotional expression via both of these media, are made much more difficult in the case of hearing impairment. Chiefly, this is because relevant acoustic cues are less clearly audible, owing to both hearing loss in itself, and the limitations of available hearing prostheses. This thesis focussed specifically on two such devices, the cochlear implant (CI) and the hearing aid (HA), and asks two overarching questions: how do users approach music and speech perception tasks, and how can performance be improved? The first part of the thesis considered auditory perception of emotion by CI users. In particular, the underlying mechanisms by which this population perform such tasks are poorly understood. This topic was addressed by a series of emotion discrimination experiments, featuring both normal-hearing (CI-simulated) participants and real CI users, in which listeners heard stimuli with processing designed to systematically attenuate different acoustic features. Additionally, a computational modelling approach was utilised in order to estimate participants' listening strategies, and whether or not these were optimal. It was shown that the acoustic features attended to by participants were a compromise of those generally better-preserved by the CI, and those particularly salient for each stimulus. In the latter half of the thesis, the nature of assessment of music perception by hearing-impaired listeners was considered. Speech perception has typically taken precedence in this domain which, it is argued, has left assessment of music perception relatively underdeveloped. This problem was addressed by the creation of a novel, psychoacoustical testing procedure, similar to those typically used with speech. This paradigm was evaluated via listening experiments with both HA users and CI-simulated listeners. In general, the results indicated that the measure produced both valid and reliable results, suggesting the suitability of the procedure as both a clinical and experimental tool. Lastly, the thesis considered the consequences of the various findings for both research and clinical practice, contextualising the results with reference to the primary research questions addressed, and thereby highlighting what there is left to discover

Investigating the build-up of precedence effect using reflection masking

The auditory processing level involved in the build‐up of precedence [Freyman et al., J. Acoust. Soc. Am. 90, 874–884 (1991)] has been investigated here by employing reflection masked threshold (RMT) techniques. Given that RMT techniques are generally assumed to address lower levels of the auditory signal processing, such an approach represents a bottom‐up approach to the buildup of precedence. Three conditioner configurations measuring a possible buildup of reflection suppression were compared to the baseline RMT for four reflection delays ranging from 2.5–15 ms. No buildup of reflection suppression was observed for any of the conditioner configurations. Buildup of template (decrease in RMT for two of the conditioners), on the other hand, was found to be delay dependent. For five of six listeners, with reflection delay=2.5 and 15 ms, RMT decreased relative to the baseline. For 5‐ and 10‐ms delay, no change in threshold was observed. It is concluded that the low‐level auditory processing involved in RMT is not sufficient to realize a buildup of reflection suppression. This confirms suggestions that higher level processing is involved in PE buildup. The observed enhancement of reflection detection (RMT) may contribute to active suppression at higher processing levels