Perceptual processing in individuals with autism
The aim of this thesis was to explore perceptual processing in individuals with autism and Asperger's syndrome, and to assess the extent to which the theory of weak central coherence could account for any abnormalities in this area. In Experiment 3:1 we presented individuals with autism with four illusions on a computer and asked them to adjust certain parts to appear the same. The results showed just as susceptible to illusions as those without autism on a computer task contrary to previous literature (Happe, 1996). In Experiment 3:2 we presented the same illusions on card and asked participants to judge whether parts of the stimuli were the same or different as in Happe's procedure. Our results showed that autistic populations succumbed to illusions regardless of whether they verbally judged or manually made adjustments to the stimuli. This ruled out the possibility that procedural differences could account for our failure to replicate Happe's findings. These results show that coherence is intact at low levels of perceptual processing in autism. Our second study (Experiment 4:1) explored whether individual differences in coherence may be able to explain why the results of Experiments 3:1 and 3:2 were not consistent with Happe's findings. We presented a battery of visuo-spatial tasks (block design, embedded figures, Rey complex figure test) and the visual illusion computer task to participants. Performance on these tasks was unable to predict susceptibility to visual illusions, suggesting that perception of illusions may not be related to weak central coherence. Our final investigation explored whether autistic populations were more inclined to rely on visual rather than semantic properties when asked to pair atypically coloured pictures (e. g. blue banana) with colour patches (e. g. yellow or blue). Those with autism relied on background knowledge like control participants choosing the semantically related colour. We then considered whether requiring the participants to name the object before selecting a colour may have influenced them to choose the semantic alternative in Experiment 5:2. Those with autism performed similarly to comparison groups choosing the semantic rather than the visual option. This demonstrated that background knowledge was just as salient to those with autism and Asperger's syndrome as those without autism.