Autism does not simply affect how people relate to others but has a wide range of effects, a study suggests.
Autism affects the way brain communication, the study suggests
US researchers compared 56 children with autism with 56 who did not have the condition.
Those with autism were found to have more problems with complex tasks, such as tying their shoelaces, suggesting many areas of the brain were affected.
A UK autism expert said the Child Neuropsychology study showed how pervasive the condition was.
People with autism are traditionally identified as having problems interacting with others and with both verbal and non-verbal communication.
They can also display repetitive behaviours and have very focused interests.
But this study suggests autism can affect sensory perception, movement and memory because it prevents different parts of the brain working together to achieve complex tasks.
The children with autism all had the ability to speak, read and write.
All those studied by the team from the Collaborative Program of Excellence in Autism were aged eight to 15.
While children with autism performed as well as, and sometimes better than, the other children in basic tests, they all had trouble with complex tasks.
So in the visual and spatial skills tests, children with autism were very good at finding small objects in a busy picture, such as finding the character Waldo in the "Where's Waldo" picture books series.
But when they were asked to tell the difference between similar-looking people, they found it very difficult.
And while children with autism tended to be very good at spelling and grammar, they found it much harder to understand complex figures of speech, such as idioms - where the meaning of the phrase is not the same as the actual words suggest.
For example, they would not understand "He kicked the bucket" as meaning someone had died and were likely to actually hop if told to "hop it".
Children with autism also had problems with their handwriting.
Nancy Minshew, a specialist in psychiatry and neurology at the University of Pittsburgh School of Medicine, who led the research, said: "These findings show that you cannot compartmentalise autism. It's much more complex.
She said researchers investigating autism needed to look for causes that affect multiple brain areas, rather than simply looking at areas related to communication and repetitive behaviours or obsessive interests.
Dr Minshew added: "Our paper strongly suggests that autism is not primarily a disorder of social interaction but a global disorder affecting how the brain processes the information it receives - especially when the information becomes complicated."
The team has previously found, through looking at brain scans, that people with autism have abnormalities in the neurological wiring through which brain areas communicate.
She said these abnormalities were the most likely explanation for why the children with autism in the current study had problems with complex tasks but did well in tasks that only required one region of the brain.
Professor Simon Baron Cohen, head of the Autism Research Centre in Cambridge, said: "This new study is important in highlighting atypical functioning in both social and non-social domains, by people with autism spectrum conditions.
"Previously the social difficulties have received a great deal of research attention.
"But this new study reminds us that the causes of autism have more pervasive effects."