Impaired metaphor comprehension in individuals with autistic spectrum disorder as symptom of impaired interhemispheric coordination and functional connectivity


Impaired metaphor comprehension has been widely reported in the autistic population. Autistic adults with a typical IQ, vocabulary, and linguistic competence still underperform on metaphor comprehension tasks. Several explanations for this have been proposed- impaired theory of mind, weak central coherence, low verbal IQ, a lack of prior semantic knowledge, problems with information integration, or some form of hemispheric dysfunction within the autistic brain. However, the evidence in support of these proposals is equivocal. In this thesis, I contend that impaired metaphor comprehension in autistic individuals is not, in fact, caused by the dysfunction of a single skill, or a single area of the brain. A review of the literature suggests instead that impaired metaphor comprehension is due to pervasive, systematic differences in the autistic brain. These differences make various linguistic tasks more effortful for autistic individuals than they are for neurotypical individuals – and, as figurative language and metaphor comprehension are high-effort tasks with a high processing load, these competencies are disproportionately affected. Impaired interhemispheric communication and impaired functional connectivity (specifically a frontal-posterior connectivity impairment that affects synchronization of activity in Wernicke’s and Broca’s areas) mean that the neurological functions required for metaphor comprehension (i.e. transfer of information between hemispheres, and coordination of Wernicke’s and Broca’s areas) are more demanding for the autistic brain. An atypical lack of lateralization of linguistic functions in the autistic brain compounds this problem, necessitating even more widespread information transfer. Additionally, autistic individuals display decreased activation in areas of the brain involved with mediating executive functioning-related process that are essential to metaphor comprehension, such as retrieval of prior semantic knowledge, selection between competing semantic alternatives, verbal processing, and working memory. (Supervised by Dr. Richard Breheny.)

Thesis for BA Hons in Linguistics at University College London