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

Abstract

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.

Keywords:

• Reading
• Visual deficits
• Developmental dyslexia
• Orientation deficit
• Williams syndrome

Acknowledgments

We would like to acknowledge the support of NIH grant DC006740 to BR and NINDS RO1 NS 050876 to BL as well as an NRSA grant F31HD056629 from the National Institute of Child Health And Human Development, and a Provost's Career Enhancement Postdoctoral Scholarship from the University of Chicago to BD. We would also like to thank Danny Dilks and Emma Gregory for providing us WS group data for the Benton and Orientation Matching tasks. Finally we deeply appreciate the participation of BMP and HFK.

Notes

¹This genetic heterogeneity makes a strong case for using case study approach with this population, either as a separate method by itself or in combination with group studies.

² The WS group in this study had a mean chronological age of 16 years 9 months (range = 10–26 years). The mean overall KBIT IQ for this group of WS participants, as well as the groups we report on in the next two tasks, was 63 (range = 40–72) and they scored an average age equivalent of 9 years 8 months on the KBIT verbal subtest (range = 6;6–14;8) and an age equivalent of 7 years 1 month on the KBIT matrices (range = 5;0–9;3). Moreover, because people with WS often fail to pass the pretest for this task (e.g., Wang, Doherty, Rourke, & Bellugi, 1995), Dilks et al. administered all the trials, even to those participants that failed the pretest and reported on the number correct for each WS individual.

³ The WS group had a mean chronological age of 22 years 9 months (range = 16;10–28;5).

⁴ The WS group had a mean chronological age of 18 years 7 months (range = 11–30 years).

⁵ Although these results might, on the surface, seem to suggest that BMP does not have a visual deficit this is not the case. In fact, the 16-year-old BMP often performs as well as 6-year-old typically developing children while the 16-year-old HFK often performs as well as 4-year-old typically developing children. For example, on the Delayed Block Matching task, BMP performs no differently than typically developing 6-year-olds (N = 12, Mean for 6-year-olds = 22.33, Crawford's t(11) < 1, p = ns). But he is significantly more accurate than typically developing 4-year-olds (N = 12, Mean for 4-year-olds = 15.4, Crawford's t(11) = 2.36, p < .05; data for 4- and 6-year-olds from Dessalegn & Landau, 2008, 2009). Whereas, HFK performs no differently than typically developing 4-year-olds (Crawford's t(11) < 1) but is significantly worse than typical 6-year-olds (Crawford's t(11) = 2.89, p < .05). Similarly, on the Orientation Matching Task-Memory Condition, BMP's score was higher than normally developing 4-year-olds (average for 4-year-olds = 26/64; Crawford's t(15) = 3.85, p < .01) but no different from 6-year-olds (average for 6-year-olds = 39/64; Crawford's t(11) = 1.36, p > .05). It is hard to tell whether BMP's performance on these tasks is exactly equivalent to normal 6-year-olds, because of ceiling effects (for both the normal 6-year-olds and BMP). However, we can safely say that he performs better than normal 4-year-olds, and as well as children 6 years old or older.

⁶ Further, we cannot rule out the rather unlikely account that HFK suffered from phonological deficits earlier in life which were later remediated, but that the remediation did not then benefit her written language skills.