2.3 Other points for diagnostic consideration
Besides having ‘criterial’ symptoms, many people with autism have additional difficulties. For instance, they may experience perceptual distortions such as perceiving normal noises as extremely loud and disturbing. These features are not always present, and are not specific to autism. It has been suggested that problems such as dyslexia and ADHD similarly have some shared features. Omitting such shared features from criteria helps to ensure that they discriminate autism from other disorders.
Peeters and Gillberg (1999) state that 80 per cent of children who meet the criteria for classic autism score below 70 on psychometric tests of intelligence (IQ tests), which places them in the range associated with severe intellectual impairment. Most of the remaining children with this diagnosis score in the range 70 – 100, which is still at the low end of the range statistically defined as normal.
Given the communication problems in autism, why might there be difficulty interpreting these I.Q. findings?
It is difficult to know how far autistic children's performance on IQ tests is independent of their language difficulties. Many IQ tests include specific tests for verbal skills, and all IQ tests require an understanding of verbal instructions. Some researchers and practitioners argue that it is difficult or impossible to provide a measure of I.Q. that is uncontaminated by language difficulties.
Some people with autism have exceptional skills in one particular area. For instance, children whose overall level of I.Q. performance is low, are often exceptionally good at particular sub-tests such as the ‘block design’ and ‘embedded figures’ tests shown in Figure 2 . In the block design test (a), the task is to select blocks as necessary to make up the same design as is shown at the top. In the embedded figures test (b), the task is to locate a shape within the pram pattern that matches the separate triangle.
A small proportion of people with autism have outstanding talents known as savant skills . Some are musically gifted, while others can accomplish astonishing feats of memory or mental arithmetic. These will be discussed further in Section 3 .
To make a full evaluation of such complex and varied manifestations, diagnosis is typically a multi-stage process in which a system such as DSM-IV-TR™ is just one of many tools employed. Practitioners will draw on multiple sources of information, including face-to-face encounters, discussions with family and the family doctor, and detailed observation of behaviour. They may use a specially structured schedule of observations and questions that enables them to chart communication, social behaviour and other activities, using standardised tasks, to ensure that all areas of the diagnostic criteria are assessed.
Savant skills : Exceptional talents, typically in an area such as music, art or mathematics, possessed by a person who is otherwise intellectually disabled.