Does a Visual-Orthographic Deficit Contribute to Reading Disability?

Annals of Dyslexia, Jun 2005 by Badian, Nathlie A

In this study, visual-orthographic skills were defined as the ability to recognize whether letters and numerals are correctly oriented. Aims were to investigate whether visual-orthographic skills would contribute independent variance to reading, and whether children with a visual-orthographic deficit would be more impaired readers than similar children without this deficit. Participants were 207 children, aged 8 to 10 years, who attended school in a small suburban community. Because of the evidence that phonological awareness and naming speed are strongly related to reading, visual-orthographic skills were entered into hierarchical regression analyses following these variables. With age, verbal IQ, and verbal short-term memory also controlled, visual-orthographic skills accounted for significant independent variance in all reading measures. When children with a visualorthographic deficit (29% of the sample) were compared with those without this deficit, they were significantly lower on all reading variables. At 8 to 10 years of age, reading progress of some children continues to be hampered by a problem in orthographic memory for the orientation of letters and numerals. Such children will require special attention, but their problems may be overlooked. As recommended by Willows and Terepocki (1993), there is need for further research on the phenomenon of letter reversals when they occur among children beyond first grade.

Key Words: Letter orientation, low level visual processing, naming speed, phonological awareness, reading disability, visual-orthographic skills

For the past 20 years or more, the impetus in dyslexia research has been to prove that the underlying cause of reading difficulties is poor phonological awareness (Brady & Shankweiler, 1991; Rack & Olson, 1993; Torgesen, Wagner, & Rashotte, 1994; Wagner & Torgesen, 1987). Serial naming speed was included under the rubric of phonological awareness by Wagner and Torgesen (1987). Evidence has been mounting, however, that naming speed contributes variance to reading independently of phonological awareness (Badian, 1993a; Barker, Torgesen, & Wagner, 1992; Manis, Doi, & Bhadha, 2000; Olson, Forsberg, & Wise, 1994). Numerous studies have shown that naming speed is significantly correlated with reading and differentiates between normal and disabled readers (Cornwall, 1992; McBrideChang & Manis, 1996; Meyer, Wood, Hart, & Felton, 1998; Wolf, 1991, 1997). The conviction that, in addition to phonological awareness, naming speed is an important facilitator of reading skills, led to the double-deficit hypothesis (Wolf & Bowers, 1999, 2000). According to this hypothesis, some poor readers have a single phonological or naming speed deficit, and some have both deficits (the "double deficit " group). The double deficit group is the most impaired in reading skills.

THE ROLE OF THE VISUAL SYSTEM IN DYSLEXIA

The visual system, as well as the auditory, is involved in learning to read (Chase, 1996; Ehri & Wilce, 1985), and it is difficult to determine which system is more critical for reading development (Chase, 1996). In spite of the venerable history of visual deficits in dyslexia that goes back to Hinshelwood (1895) and Pringle Morgan (1896), interest in this aspect of dyslexia research has been minimal in recent years. Neglect of the contributions of the visual system to reading intensified following the publication of Vellutino's (1979) authoritative book on dyslexia, which made a strong case for linguistic deficits as the cause of dyslexia and stressed the lack of evidence for visual deficits. These conclusions have been criticized (Fletcher & Satz, 1979; Willows, Kruk, & Corcos, 1993). Stanovich (1992) cites several studies that found differences between disabled and nondisabled readers in visual experiments using nonverbal stimuli, brief presentations, and psychophysical procedures. He points out that much of the evidence contradicting the idea of visual deficits in reading disability comes from studies employing arrays exposed for several seconds or more.

Visual deficits potentially associated with reading disability range from poor performance on low level visual processing tasks to difficulties with complex visual-orthographic measures. In their causal model for visually based reading impairments, low level visual processing leads either to the visual (object) processor or to the visual (orthographic) processor (Seymour & Evans, 1993). The route from the visual (orthographic) processor then leads to central reading processes. The following brief review will examine studies of the relationship of low level visual tasks to reading, visual-orthographic (surface) subtypes of dyslexia, and letter recognition and orientation problems in dyslexia.

LOW LEVEL VISUAL PROCESSING AND READING

In a number of recent experiments, low level visual tasks such as visual motion, contrast sensitivity, visual tracking, and temporal processing have been shown to correlate with reading, and, at least in some studies, to differentiate between groups of good and poor readers (Boden & Brodeur, 1999; Booth, Perfetti, MacWhinney, & Hunt, 2000; Cornelissen & Hansen, 1998; Eden, Stein, Wood, & Wood, 1995; Iles, Walsh, & Richardson, 2000; Olson & Datta, 2002; Stein, Talcott, & Witton, 2001; Talcott et al., 2002).