Social deficits distinguish autism from other developmental disorders. People with autism have social impairments and often lack the intuition about others that many people take for granted. For instance, when we can often guess if a person is happy or sad based on her body language and tone of her voice, people with autism often can't read such things unless it's explicitly stated.
Contrary to common belief, autistic children do not prefer being alone. Making and maintaining friendships often proves to be difficult for those with autism. For them, the quality of friendships, not the number of friends, predicts how lonely they feel. Functional friendships, such as those resulting in invitations to parties, may affect the quality of life more deeply.
There are many anecdotal reports, but few systematic studies, of aggression and violence in individuals with autism. The limited data does suggest that people with more severe autism are more prone to throwing aggressive tantrums and violent behavior.
About a third to a half of individuals with autism do not develop enough natural speech to meet their daily communication needs. They will be able to pronounce less words and vocal patterns and have even lesser gestures to go with their words. They will also be less likely to make requests or share their experiences.
Autistic people are less likely to make requests or share experiences, and are more likely to simply repeat others' words. Joint attention seems to be necessary for functional speech, and deficits in joint attention seem to distinguish infants with ASD: for example, they may look at a pointing hand instead of the pointed-at object, and they consistently fail to point at objects in order to comment on or share an experience. Autistic children may have difficulty with imaginative play and with developing symbols into language.
Studies shown that even higher-functioning autistic people are not used to complex language tasks such as figurative language, comprehension and inference. However, they DO tend to do well at basic things such as vocabulary and spelling – and this is what is more observable externally. This creates an initial impression that they do understand their language well, and people speaking to autistic individuals are likely to overestimate what their audience comprehends.
Autistic individuals display many forms of repetitive or restricted behavior, which are categorised as follows.
Stereotypy is a repetitive movement, such as hand flapping, making sounds, head rolling, or body rocking.
Compulsive behaviour is intended and appears to follow rules, such as arranging objects in stacks or lines.
Sameness is resistance to change; for example, insisting that the furniture not be moved or refusing to be interrupted.
Ritualistic behaviour involves an unvarying pattern of daily activities, such as an unchanging menu or a dressing ritual. This is closely associated with sameness and an independent validation has suggested combining the two factors.
Restricted behaviour is limited in focus, interest, or activity, such as preoccupation with a single television program, toy, or game.
Self-injury includes movements that injure or can injure the person, such as eye poking, skin picking, hand biting, and head banging. A 2007 study reported that self-injury at some point affected about 30% of children with ASD.
No single repetitive behavior seems to be specific to autism, but only autism appears to have an elevated pattern of occurrence and severity of these behaviors.
Autistic individuals may have symptoms that are independent of the diagnosis, but that can affect the individual or the family.
An estimated 0.5% to 10% of individuals with ASD show unusual abilities, ranging from splinter skills such as the memorization of trivia to the extraordinarily rare talents of prodigious autistic savants.
Many individuals with ASD show superior skills in perception and attention, relative to the general population.
Sensory abnormalities are found in over 90% of those with autism, and are considered core features by some, although there is no good evidence that sensory symptoms differentiate autism from other developmental disorders.
Differences are greater for under-responsivity (for example, walking into things) than for over-responsivity (for example, distress from loud noises) or for sensation seeking (for example, rhythmic movements). An estimated 60%–80% of autistic people have motor signs that include poor muscle tone, poor motor planning, and toe walking; deficits in motor coordination are pervasive across ASD and are greater in autism proper.
Unusual eating behavior occurs in about three-quarters of children with ASD, to the extent that it was formerly a diagnostic indicator. Selectivity is the most common problem, although eating rituals and food refusal also occur; this does not appear to result in malnutrition.
Parents of children with ASD have higher levels of stress. Siblings of children with ASD report greater admiration of and less conflict with the affected sibling than siblings of unaffected children or those with Down syndrome; siblings of individuals with ASD have greater risk of negative well-being and poorer sibling relationships as adults.