Understanding the electrophysiological development of the auditory response to speech in normal hearing (NH) individuals is a necessary step in identifying abnormal speech processing delays in children with speech perception deficits. I will characterize the development of the auditory response to speech electrophysiologically using electroencephalography (EEG). I will identify age-specific templates of the neural oscillations that distinguish the processing of temporal (Aim1) and spectral (Aim2) properties of speech, specifically the onset rise time (ORT) and formant structure, respectively. Electrophysiological changes will be assessed based on three dimensions representing the dynamics of brain oscillatory activity: (1) the strength of temporal alignment of the neural response to the acoustical property, referred to as phase-locking index (PLI), (2) the spectral power of the neural response (SP), and (3) the latency of PLI or SP responses with respect to the onset of speech. These measures reflect different neural mechanisms that may be specific to certain speech properties. Based on behavioral measures, children weight formant trajectories more so than envelope structure when processing speech sounds. As they age, they learn to utilize envelope information (e.g. ORT) provided by the speech signal. In comparison to behavioral findings, EEG results revealed that PLI of low- frequency oscillatory activity is associated with coding spectral aspects of sounds in children, while adults utilize low- and high-frequency PLI for processing spectral information of sound. Also, PLI latency is associated with processing the ORT. PLI latency of the low- and mid-frequency oscillatory activity starts to shift with ORT around age 7-9. Together, behavioral and electrophysiological findings point to a possible role of low- and high-frequency PLI in development of formant processing, and a role for PLI latency of low- and mid-frequency oscillatory activity in development of ORT processing. Age- templates based on this study will subsequently be used to identify auditory response development for the temporal and spectral processing of speech in children with speech perception deficits.
The proposed research will help expand our current knowledge of auditory cortex development in normal hearing children. We will identify specific brain activity associated with the development of specific speech properties. In the future, we will use the knowledge obtained from this research to assess auditory development in children with speech and language deficits.
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