Consequences of severe visual-spatial deficits for reading acquisition: evidence from Williams syndrome.

To further understand the nature of the visual-spatial representations required for successful acquisition of written language skills, we investigated the written language abilities of two individuals with Williams syndrome (WS) a developmental genetic disorder in which the presence of severe visual-spatial developmental delays and deficits has been well established. Using a case study approach, we examined the relationship between reading achievement and general cognitive ability, phonological skills, and visual-spatial skills for the two individuals. We found that, despite the strong similarity between the two individuals in terms of their verbal and non-verbal cognitive abilities and their phonological abilities (as well as chronological age and educational opportunities), their reading and spelling abilities differed by more than 5 grade levels. We present evidence that the difference in written language performance was likely to be due to differences in the severity and nature of their visual-spatial impairment. Moreover, we show that specific difficulty processing the orientation of visual stimuli is related to the reading difficulties of one of the two individuals. These results underscore the contribution of visual-spatial abilities to the reading acquisition process and identify WS as a potential source of valuable information regarding the role of visual-spatial processing in reading development.