believed that these problems were related to the left hemisphere of the brain, which

controls the storage of visual memory because these children seemed to have difficulty

remembering names of letters and words (Clark & Uhry, 1995). In 1928, Samuel Orton,

an American neurologist, theorized that people perceive visual inputs from both right and

left visual fields and relay this input as mirror images to the visual cortices (Clark &

Uhry, 1995). For most people, one side of brain becomes dominant over the other and

suppresses the image from the non-dominant hemisphere; however, he believed some

people who poorly perform 'dominance', may perceive backward images. He believed

this poor dominance might produce reading problems (Clark & Uhry, 1995). Therefore,

from the early 20th century, vision research related to RD has been continuously

undertaken. However, researchers revealed that reversal and sequencing errors did not

appear in a large proportion of people with RD, and most of people with RD showed

more oral reading errors. Moreover, Vellutino (1978, 1983) indicated that poorer readers

are as good as nondisabled readers on copying confusable letters and words from

memory. Rather, they showed problems at naming and pronouncing the items. With these

findings, he concluded that visual deficits could not explain RD. Moreover, several major

reviews of the evidence concluded that visual deficits are not a major cause of reading

disability (Stanovich, 1982; Velluntino, 1979). Since then, numerous studies have

demonstrated that understanding the sound structure of language (phonological

awareness) is a strong predictor of reading success.

 In contrast, studies on visual processing factors have been under heavy attack by

reading researchers during the last three decades. As discussed earlier, inconsistent and

conflicting findings have fueled the debate and have hindered research on visual