Associated features
COGNITIVE IMPAIRMENT
Approximately 75 to 80 percent are mentally retarded, with the majority functioning in the moderate range of retardation. The retardation is not a consequence of social isolation, lack of motivation, or negativity while taking intelligence tests. Autistic persons show a distinctive pattern on intelligence tests in that they perform worse on subtests that require verbal sequencing and abstraction abilities, such as the comprehension subtest, than on subtests that measure visual-spatial or rote memory skills, such as the information and block design subtests. Indeed, autistic children may perform better than matched controls on tests such as the embedded figures test, in which a smaller figure has to be discovered in a larger figure, paradoxically as a result of a cognitive deficit whereby context is ignored. Thus, performance scores are usually higher than verbal scores (although the reverse is often true in persons with Asperger’s disorder).
Those findings and other findings from cognitive experiments have led to cognitive theories of autism. One hypothesis is that the lack of a central drive for coherence underlies the autistic disorder, creating both a fragmentary experience of the world and detachment from it. Another hypothesis is that autism is caused by the child’s inability to attribute mental states to others, so that a theory of mind, whereby one person predicts another person’s behavior by inferring his or her thoughts, beliefs, and feelings, is not developed. That theory would account for the lack of empathy and social cognition seen in autistic individuals. However, it does not account for the absence of basic social behaviors in autistic children before the age when a theory of mind develops. In addition, at least two studies have shown that people with Asperger’s disorder are capable of solving problems requiring second-order thought attributions (predicting another person’s behavior based on that person’s belief about still another person’s belief) but still show severe social impairment.
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Intriguingly, some autistic persons exhibit so-called islets of abilities or splinter skills, such as perfect pitch or an excellent rote memory, or the ability to read material at a level far beyond that expected from intellectual performance (hyperlexia). Fifty percent of idiot savants -mentally retarded persons displaying extraordinary skills, such as calendar calculating, executing accurately detailed drawings of scenes from memory, or playing a piece of music after hearing it only once–are autistic.
ABNORMALITIES OF MOTOR BEHAVIOR
Most autistic children display stereotypies, such as hand flapping and rocking, with the most severe stereotypies occurring in the most intellectually impaired. Motor mannerisms may be seen, such as odd posturing or “air writing,” so named independently by two autistic boys who, for their own amusement, would spell words by tracing the letters with their index fingers in the air. Hyperactivity is common, especially in preschoolers. On the other hand, some children may be hypoactive, or hypoactivity may alternate with hyperactivity. Some children with pervasive developmental disorder exhibit inattention and impulsivity. There may be motor incoordination, tiptoe walking, and the assumption of odd postures. Some children are clumsy and may have trouble learning to tie shoelaces, brush their teeth, cut up food, or button shirts. There may be a delay in the disappearance of mirror movements.
ABNORMAL RESPONSES TO SENSORY STIMULI
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Some children exhibit hypersensitivity to sound (hyperacusis) and cover their ears when they hear loud noises such as firecrackers exploding, dogs barking, or police sirens wailing. Other children may appear oblivious to loud noise but may be fascinated by the faint ticking of a wristwatch or the sound of crumpling paper. Bright light, including the examining light at the dentist’s office, may be distressing, although some children are fascinated by lights. There may be extreme sensitivity to touch, and wearing certain clothes (of rough fabrics such as wool, or clothes with prickly labels) or even switching from short-sleeved to long-sleeved shirts when the weather changes may lead to tantrums. Some children, on the other hand, appear insensitive to pain and may not cry after a severe injury. Children may be fascinated by certain sensory stimuli, such as spinning objects, and many enjoy the stimulation of twirling, apparently not getting dizzy.
