The Neuroanatomical Origin of Severe Speech Impairment in Autism

Autistic individuals’ delay and, for some, continued impairment in speech are typically ascribed to intellectual impairments or social affiliation deficits. Indeed, autistic individuals whose speech does not develop to fluency are often referred to as “low functioning,” and are sure to be disadvantaged on many measures of intelligence. However, when assessed without demand on speech production, minimally fluent autistic individuals excel on the preeminent test of fluid intelligence. Similarly, although theoretical speculations continue to misperceive autism as an attachment disorder, all empirical studies demonstrate that autistic individuals are as securely attached to their primary caregivers as their peers.

In contrast to socioemotional or intellectual attributions for autistic individuals’ severe speech impairment, the research of Gernsbacher and colleagues has implicated oral- and manual-motor development. It should be noted that language is the mental representation of concepts, whereas speech is literally the articulation of language. Speaking fluently requires “an intricate orchestration” of oral-motor mechanisms.

The prominent associations among oral- and manual-motor skills and speech fluency which Gernsbacher and colleagues have documented in previous research, bear striking implications for appreciating communication impairment in autism. For instance, these associations challenge the common assumption that manual modes of communication, including those that require keyboarding, are available to autistic individuals – if simply they choose to use them.

This project was motivated by two important findings: (1) a neuroanatomical marker of individuals with speech impairment, and (2) a manual-motor behavioral marker of individuals with severe speech impairment that could be related to the neuroanatomical marker. Therefore, the purpose of the project was to explore the inter-relations among speech fluency, neuroanatomical structure, and manual dominance.