Doctoral Dissertation Research: Determining the mechanisms of spoken language processing delay for children with cochlear implants

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This research project seeks to better understand how children with cochlear implants (CIs) understand spoken language in real time. CIs have transformed the lives of children who are born Deaf, enabling them to hear via electrical stimulation of the auditory nerve. However, the CI does not deliver the same signal to the brain that a typical ear does. In fact, the transformation of the acoustic input into electric hearing degrades the speech signal, making it harder to understand. The objective of this project is to determine how the degraded CI signal impacts spoken language processing by children with CIs in order to better understand how the quality of speech input impacts the development of speech perception and spoken language. The findings from this research will be shared with researchers in the field as well as schools, clinicians, families, and other parties who regularly work with children who are Deaf or Hard-of-Hearing. This communication will promote translational applications such as the development of more accurate assessment protocols, targeted treatment approaches, and policy recommendations related to pediatric cochlear implantation. By helping explain how children acquire language with the speech input they perceive, the results will help parents better understand how to interact with their children to support spoken language learning. This research project uses eye-tracking and electroencephalography (EEG) to identify the cognitive mechanisms underlying observed delays in spoken language processing by children with CIs. The first objective is to determine the source of observed delays in spoken word recognition by distinguishing between two hypotheses: 1) Delays are the result of increased competition between words, specifically for phoneme distinctions relying on spectral cues (e.g., sip vs. ship) that are not transmitted well by the CI; or 2) Children with CIs adopt a "wait-and-see" strategy for all words, regardless of how well the CI conveys the acoustic features of any particular word. The second objective is to determine how delays in spoken word recognition hinder access of semantic information by distinguishing between two hypotheses: 1) Children with CIs exhibit cascading processing of spoken words, meaning ambiguities in speech perception would result in less robust activation of a more distributed network of similar-sounding words and their semantic associates; or 2) Children with CIs demonstrate more serial processing of spoken words, in which ambiguity at the speech sound level delays activation of higher-level language networks. These findings will provide an important step forward in understanding how the quality of speech input impacts processing mechanisms underlying language comprehension, advancing theories of spoken language processing along with informing spoken language intervention for children with CIs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.