FMRI of phonemic perception and its relationship to reading development in elementary- to middle-school-age children

Neuroimaging studies suggest that categorical perception of speech phonemes in adults is primarily subserved by a pathway from bilateral primary auditory areas to association areas in the left middle superior temporal cortex, but the neural substrates underlying categorical speech perception in children are not yet known. Here, fMRI was used to examine the neural substrates associated with phoneme perception in 7- to 12-year-old children as well as the relationships among level of expertise in phoneme perception, the associated activation, and the development of reading and phonological processing abilities. While multiple regions in left frontal, temporal, and parietal cortex were found to be more responsive to phonemic than nonphonemic sounds, the extent of left lateralization in posterior temporal and parietal regions during phonemic relative to nonphonemic discrimination differed depending on the degree of categorical phoneme perception. In addition, an unexpected finding was that proficiency in categorical perception was strongly related to activation in the left ventral occipitotemporal cortex, an area frequently associated with orthographic processing. Furthermore, in children who showed lower proficiency in categorical perception, the level of categorical perception was positively correlated with reading ability and reading and reading-related abilities were inversely correlated with right mid-temporal activation in the phonemic relative to nonphonemic perception contrast. These results suggest that greater specialization of left hemisphere temporal and parietal regions for the categorical perception of phonemes, as well as activation of the region termed the visual word form area, may be important for the optimal developmental refinement of both phoneme perception and reading ability.