Ph.D. Research Proposal Exam: I.M Dushyanthi Karunathilake

Tuesday, June 28, 2022
9:00 a.m.
AVW 2328
Emily Irwin
301 405 0680

ANNOUNCEMENT: Ph.D. Research Proposal Exam


Name: I.M Dushyanthi Karunathilake



Professor Jonathan Z. Simon (Chair)

Professor Behtash Babadi

Professor Carol Epsy-Wilson

Date/time: 6/28/2022 , 9 AM

Location: AVW 2328 



Abstract: Speech comprehension is a challenging problem that requires resolving a rapidly varying signal over different speech landmarks along with cognitive processes in an approximately time-locked manner. Behavioral measures have shown that speech comprehension is altered by the age-related changes, linguistic content and intelligibility, yet the systematic neural mechanisms underlying these changes are not well understood. This thesis proposal aims to explore how the neural bases are modulated by each of these factors in three experiments by comparing speech representation in the cortical responses, measured by Magnetoencephalography (MEG). We use neural encoding (temporal response functions (TRFs)) and decoding (reconstruction accuracy) models which describe the mapping between stimulus features and the neural responses, which are instrumental in understanding cortical temporal processing mechanisms in the brain. Firstly, we investigate age-related changes in timing and fidelity of the cortical representation of speech-in-noise. Understanding speech in a noisy environment becomes more challenging with age, even for healthy aging. Our findings demonstrate that some of the age-related difficulties in understanding speech in noise experienced by older adults are accompanied by age-related temporal processing differences in the auditory cortex. This is an important step towards incorporating neural measures to both diagnostic evaluation and treatments aimed at speech comprehension problems in older adults. Next, we investigate how cortical representation of speech is influenced by the linguistic content by comparing neural responses to non-speech, narrated non-words, scrambled words and narrative passages. We show that the cortical responses time-locks to emergent features from acoustics to linguistic processes at the sentential level as incremental steps in the processing of speech input occur. Our results also suggest that at what stages speech representations are modulated by bottom-up and top-down mechanisms. Finally, we propose a new study to investigate how intelligibility affects the speech representation in the cortical response using a priming paradigm, where intelligibility is varied while keeping the acoustic structure constant. We expect that higher-level speech representations will emerge along with top-down neural mechanisms, as the speech becomes intelligible. Taken together, this thesis proposal furthers our understanding on neural mechanisms underlying speech perception, comprehension and objective neural measures to evaluate the level of speech comprehension.

Audience: Graduate  Faculty 

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