Dyslexia, reasoning and the importance of visual-spatial processes

This chapter will present some research which has aimed to investigate how people with dyslexia draw on distinctly visual cognitive processes (such as visual imagery and visual memory) when reasoning with problems comprised of logical arguments. Although such problems may appear circumscribed, they encapsulate many of the elements involved in everyday reasoning and have been the subject of much research into how people manipulate and represent information when solving problems. We will discuss a series of studies which have compared dyslexic participants with non-dyslexic controls in order to examine differences in strategies adopted for a range of reasoning tasks. A consistent finding has been that most participants with dyslexia spontaneously adopt a strategy which involves the generation of detailed visual or visuo-spatial representations. Cognitive processes such as visual imagery and visual short-term memory seem to play an important role in reasoning for these individuals in terms of helping them to understand, clarify and mentally organise problem information. In contrast, non-dyslexics are able to reason using a more abstract or rule-based approach, working with information in the propositional form in which it is presented. The importance of visual processes to dyslexics is further demonstrated by converging evidence from studies using individual differences and dual-task methods. These showed that although participants performed similarly on a measure of visual memory, capacity in this domain was only predictive of reasoning accuracy for dyslexic individuals. When dyslexics are asked to perform two concurrent tasks (reasoning and remembering a visual pattern) reasoning accuracy was impaired, suggesting that a conflict of resource in the visual domain. The secondary task had no effect on reasoning for non-dyslexics. In summary, our studies indicate that visual cognitive processes such as imagery, visual mental representation and memory form a central part of reasoning in dyslexia, and may compensate for impairments in phonological processing for these individuals.