Auditory cortical narrowing to native speech: changes across development and implications for reading difficulty

Abstract

An individual’s auditory cortical processing of speech sounds is substantially influenced by one’s native language experiences. Over the course of development, the brain becomes specialized to process speech sounds that are used in ambient native language environment, a phenomenon described as ‘auditory cortical narrowing to native speech’. In the current thesis, we studied the developmental changes of auditory cortical narrowing by examining the ERP response strength of mismatch negativity (MMN) to native and to non-native speech contrasts in school-age individuals from age 6 to age 17. We found that the auditory cortical narrowing continues through late childhood and adolescent, and the degree of narrowing at brain level is correlated with behavioral-level reading fluency. Also, a lack of MMN native language effect which indicates deficient auditory cortical narrowing to native speech was found in individuals with reading difficulty. These findings in the current thesis advanced our understanding of auditory cortical narrowing to native speech over development and its relationship with reading difficulty.