Researchers at Bringham Young University showed that children with autism hang on to the association of fear for a particular object long after other children have let it go. In a series of trials, children were given a puff of air in the face after seeing a yellow card. All of the children registered fear when shown a yellow card. At some point the card associated with the puff of air was switched to a differerent color. Typical children figured this out quickly and soon lost their distrust of the yellow card. Children with autism continued to be fearful of the yellow card long after the others. The length of time they stayed fearful was related to the severity of thier autism diagnosis.
The authors conclude that this heightened sense of fear ("anxiety", in their words) is not just associated with autism but is an integral part of it.
1. Synopsis can be found at Science Daily: Mind and Brain
2. Mikle South, Tiffani Newton, Paul D. Chamberlain. Delayed Reversal Learning and Association With Repetitive Behavior in Autism Spectrum Disorders. Autism Research, 2012; DOI: 10.1002/aur.1255