Visual perception in infancy and its links to later autism

Abstract

Alterations in primary sensory areas of the brain have been suggested to be at the roots of the well-documented visual perceptual differences in autism. However, despite the possible key role these sensory processing alterations may play in the early development of autism, few studies have tried to clarify the links. Moreover, not much is known about which specific sensory alterations are most strongly linked to the core autistic symptoms. The purpose of this thesis is to increase our knowledge about whether and how visual sensory processing differences manifest during early infancy and how they relate to later development of cognitive and social communicative abilities as well as to the emerging core social domain symptoms of autism. EEG neuroimaging was used as the means of investigation into infants’ brain activities. Comparisons between infants at elevated familial likelihood of developing autism and typically developing infants were done to see how the brain activity patterns differ.

Study I inquired whether differences in low-level global and local visual (motion and form) processing at age 5 months are linked to the acquired motor and language abilities at age 14 months. Only global motion processing was found to be linked to later language ability, and this association was specific to language comprehension.

Study II inquired whether differences in low-level global and local visual (motion and form) processing at age 5 months are in any way linked to the emerging core autistic symptoms at age 36 months, and how visual cortical organization that underlies such global and local perceptions differ between infants who later develop high levels of autistic symptoms and infants who do not develop the symptoms. Furthermore, relative influences of genes and environment on these low-level visual perceptual processes were assessed. Only global motion processing was found to be linked to the emerging autistic symptoms at 36 months, and this was specific to the social domain symptoms. Accordingly, and the global motion visual cortical organization in infants with later autism was found to be distinctive from the normative infants, showing an altered balance of activity between midline and lateral area. Global motion processing was found to be lowto-moderately heritable.

Study III sought to clarify if the results of Study II could be linked to functional brain connectivity. Specifically, this study inquired whether i) visual cortical functional connectivity during processing of social and non-social stimuli at 5 months are linked to the contemporaneous global visual motion processing investigated in Study II; and ii) whether functional connectivity differences are in any way also linked to the emerging core autistic symptoms at age 36 months. Indeed, visual cortical gamma connectivity during social stimulus processing was found to be linked to global motion processing and it is also linked to the emerging autistic symptoms at 36 months. Furthermore, visual cortical theta connectivity during non-social stimulus processing was found to be strongly associated with the emerging autistic symptoms at 36 months, but not to motion processing.

In summary, the results of these three studies demonstrate that atypical global visual motion processing, possibly linked to altered functional connectivity in the visual cortex, may occupy an important position in the pathways leading to the social domain symptoms of autism.