Perceptual Plasticity in Adverse Listening Conditions: Factors Affecting Adaptation to Accented and Noise-Vocoded Speech

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Abstract

Adverse listening conditions can be a hindrance to communication, but humans are remarkably adept at overcoming them. Research has begun to uncover the cognitive and behavioural mechanisms behind this perceptual plasticity, but we still do not fully understand the reasons for variability in individual responses. The research reported in this thesis addressed several factors which would further this understanding. Study 1 examined the role of cognitive ability in recognition of, and perceptual adaptation to, accented speech. A measure of executive function predicted greater and more rapid perceptual adaptation. Vocabulary knowledge predicted overall recognition of the accented speech, and mediated the relationship between working memory and recognition accuracy. Study 2 compared recognition of, and perceptual adaptation to, accented speech with and without audiovisual cues. The presence of audiovisual cues improved recognition of the accented speech in noise, but not perceptual adaptation. Study 3 investigated when perceivers make use of visual speech cues during recognition of, and perceptual adaptation to, audiovisual noise-vocoded speech. Listeners’ eye gaze was analysed over time and related to their performance. The percentage and length of fixations on the speaker’s mouth increased during recognition of individual sentences, while the length of fixations on the mouth decreased as perceivers adapted to the noise-vocoded speech over the course of the experiment. Longer fixations on the speaker’s mouth were related to better speech recognition.Results demonstrate that perceptual plasticity of unfamiliar speech is driven by cognitive processes, but can also be modified by the modality of speech (audiovisual or audio-only). Behavioural responses, such as eye gaze, are also related to our ability to respond to adverse conditions. Speech recognition and perceptual adaptation were differentially related to the factors in each study and therefore likely reflect different processes; these measures should therefore both be considered in studies investigating listeners’ response to adverse conditions. Overall, the research adds to our understanding of the mechanisms and behaviours involved in perceptual plasticity in adverse listening conditions.

Keyword(s)

Audiovisual speech; Cognition; Eye-tracking; Speech perception

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