What can autism and dyslexia tell us about intelligence?

This paper argues that understanding developmental disorders requires developing theories and models that explicitly represent the role of general intelligence in the cognitive phenotype of the disorder. In the case of autism it is argued that the low-IQ scores of people with autism are not likely to be due to a deficit in the cognitive process that is arguably the major cause of mental retardation - namely, speed of processing - but rather low IQ reflects the pervasive and cascading effects of the deficit in the information-processing module that causes autism. In the case of dyslexia, two radically different models of reading disorder (ability = disability and a modular deficit model) are likely to be influenced by the effect of general intelligence on reading performance in ways that will remain unclear without an explicit model of how general intelligence influences reading.