Visual perception in autism spectrum disorders.

This thesis presents research conducted at the cognitive level, the neurophysiological
level and the psycho-physical level, for examining vision in ASD. The
psycho-physical findings suggest that atypical visual perception in ASD is unlikely to have
a sub-cortical origin as sub-cortical magnocellular and parvocellular pathway functioning,
and low/high spatial frequency detection in adolescents with ASD were found to be no
different from typically-developing controls. There was, however, evidence indicating local
motion direction perception deficits in the same adolescents with ASD suggesting that
atypical motion perception in ASD may have a cortical origin. Electrophysiological
investigation of low level visual perception in ASD revealed findings concurring with this
latter interpretation. More specifically, whereas visual evoked potentials demonstrated
visuo-integrative processes associated with perception of second order and hyperbolic
gratings were not atypical in children with ASD, there was increased activity of the visual
cortical region. A further gamma power analysis then demonstrated that there may be
increased neuro-connectivity within primary visual area V1 in the children with ASD.
Atypical low level visual cortical processes may result in locally-biased perceptual style
previously observed in individuals with ASD. However, a cross-cultural comparison of
perceptual style in children with ASD and TD children from Singapore and England, found
evidence suggesting that locally-biased perceptual style in ASD may not be culturally
universal. In sum, lower level visual cortical processes may be atypical in ASD, and
whether these atypicalities manifest at the higher perceptual level can be determined by
cultural variability in attention and response processes.