White-Schwoch, T. 1 , Nicol, T. 1 & Kraus, N. 1, 2
1 Auditory Neuroscience Laboratory (www.brainvolts.northwestern.edu) and Department of Communication Sciences, Northwestern University
2 Departments of Neurobiology & Physiology and Otolaryngology, Northwestern University
In a longitudinal study of child development we have found that the neurophysiological integrity with which consonants in noise are processed predicts future literacy before children learn to read, supporting the hypothesis that auditory processing is a chief factor in literacy development. We propose a model whereby timing variability in the auditory system compromises the representation of speech, undermining phonological development. This model is supported by evidence from humans that individuals with dyslexia exhibit variable neural responses to speech. We sought to test this model by directly comparing speech-evoked activity in humans and guinea pigs, capitalizing on the unique insight offered by local neural activity. We have found that timing jitter in the auditory system is expressed as variable scalp-recorded evoked potentials. This timing jitter specifically targets the neural representation of fine-grained phonemic features in speech, suggesting that individuals with excessive variability do not process these crucial features precisely. Direct comparisons between humans and an animal model present a rare opportunity to dissect the neural events that underlie biological markers of literacy in humans, and to understand the specific mechanisms by which they may constrain literacy development.
Supported by NIH (R01 DC01510 & R01 HD069414) and the Knowles Hearing Center.