Contributions of Prosodic and Lexical Cues to the Decoding of Phonetic Information from Speech

A core aspect of language comprehension is the extraction of phonetic information from speech. This process is non-trivial due to the transient nature of phonetic segments and their overlapping presence in the acoustic signal. We aim to gain a deeper understanding of this complex process in the context of dyslexia. Individuals with this reading impairment have been found to process two aspects of speech differently from typical readers: they have difficulty extracting individual phonemes from words, and they show signs of imprecise cortical tracking of the speech envelope, an important correlate of speech prosody. However, it is unclear how exactly imprecise tracking of speech leads to phoneme-level deficits. Moreover, despite these deficits, natural speech comprehension in dyslexia remains intact, suggesting that compensation may take place. We address these gaps by applying state-of-the-art phonetic decoding analyses in dyslexia for the first time while varying prosodic and lexical cues within the speech signal. A novel analytical approach will reveal how listeners with and without dyslexia track phonetic segments over time, retain their correct order, and decode them into distinct phonetic representations. Cortical responses to phonetic segments will be tracked in natural speech, in synthesised speech with impoverished prosodic cues, and in meaningless pseudospeech (Jabberwocky) while MEG data are recorded. Comparing the neural dynamics of phonetic decoding in natural speech to speech with impoverished prosodic information will show to what extent prosodic cues facilitate decoding of fine-grained phonetic information. Comparing natural speech to pseudospeech will reveal whether poor phonetic decoding can be compensated with top-down information. The project will provide a better understanding of how phonetic information is extracted from speech and how this may relate to the persistent deficits in dyslexia, with important implications for theory and remediation.