6.1 Intellectual ability

Differences in cognition, that is, in thinking, learning and problem-solving skills are often represented in terms of Intelligence Quotient (IQ). This is a standardised way of measuring intelligence using tests of both verbal and non-verbal ability. The IQ of people with autism ranges from scores of 70 and below, which corresponds to a profound intellectual disability, to 100, which is the average IQ for any population, to 130 and above, which corresponds to high or extremely high IQ.

Figure 8 The characteristic bell-shaped distribution of IQ scores within the general population. Most people’s IQ scores fall within the range 70 to 130. A minority of individuals have scores lower than 70 or higher than 130.

Show description|Hide description

This is a graph showing the average distribution of IQ scores. The X axis is labelled 'IQ score' and the Y axis is labelled 'numbers of individuals'. The graph then shows a symmetrical bell curve, showing low numbers of individuals for IQ scores below 70. The section below 70 IQ is shaded in and labelled '2.5% with intellectual disability'. The curve then rises up to the peak, reaching the mean IQ value of 100. This middle segment is labelled as containing 95% of the population. Then the curve gradually descends back down as IQ score increases. The area beyond IQ 130 is shaded and labelled '2.5% exceptionally able'.

Figure 8 The characteristic bell-shaped distribution of IQ scores within the general population. Most people’s IQ scores fall within the ...

When a person has profound intellectual disabilities, as defined by an IQ of less than 70, their autism has sometimes been described as ‘low-functioning’. This indicates that the person is profoundly affected, with overt speech and language problems, possibly being non-verbal even into adulthood. Autism in a person with an IQ of 70 or above has often been described as ‘high-functioning’. But this is misleading in several ways. Firstly, IQ scores in the range 70–99 are still below average; a person with an IQ of 85, for instance, may struggle with academic tasks. Secondly, ‘high-functioning’ might suggest that the person is not profoundly affected by their autistic symptoms. But social difficulties and repetitive behaviours can be profoundly disabling at any level of intellectual ability. For instance, an academically able autistic person may struggle to understand instructions or questions from teachers, especially if these are phrased in abstract language. They may find their learning environment stressful due to loud noise, bright lights and unusual smells, and they may expend considerable cognitive resources in ‘pretending to be normal’. Consequently, even with a high IQ, a person’s capacity to learn and thrive academically may be hampered by these additional factors. Alternatively, an academically successful person may find everyday tasks very challenging, as expressed here by Dr Wenn Lawson, writer, psychologist and autism advocate: