Phonetic Variability in Speech Perception and the Phonological Deficit in Dyslexia

Accounting for phonetic variability across talkers is a core challenge in speech perception. Cognitive models of word recognition address variability by employing either episodic or talker-normalization based approaches. In developmental dyslexia, a “phonological deficit” is thought to impair the acquisition of typical reading ability; however, no connection has yet been made between such a phonological deficit and speech perception behavior, which appears intact in dyslexia. We demonstrate differences between dyslexic listeners and controls in two tasks involving processing phonetic variability: First, dyslexics exhibited impaired talker identification abilities in a familiar language but not a foreign one. Second, the brains of individuals with dyslexia exhibited reduced hemodynamic adaptation – a neural index of talker normalization – compared to typical readers. Together, these results suggest speech perception in dyslexia relies primarily on episodic processes, and that the inability to fully utilize talker-normalization processes may impair the formation of the abstract representations of speech sounds necessary for robust sound-to-letter mapping during reading development.