Visual temporal processing deficits in specific reading disability
Specific reading disability is a broad term encompassing reading disabilities that may arise from a number of sources. A specific-reading-disabled child (SRD) is defined here as one of normal or better intelligence with no known behavioral or organic disorders who, despite normal schooling and average progress in other subjects, has a reading disability of at least 1.5 years. Because reading is a dynamic visual processing task requiring the analysis and integration of visual pattern information across fixation-saccade sequences, studies in the area of reading disability have explored the possibility that visual processing abnormalities contribute to reading difficulties. A number of studies have provided evidence for basic visual processing differences between normal and disabled readers, especially at early stages of visual processing ( Lovegrove & Brown, 1978; Stanley, 1975). These results indicate that some disabled readers process information more slowly and have a more limited processing capacity than normal readers. Studies that used tasks relying less on dynamic visual processing and temporal resolution, and more on pattern-formation processes and long-term visual memory, however, have failed to show visual processing differences between normal and disabled readers ( Benton, 1975; Vellutino, 1979), although the validity of some of these studies has been called into question ( Fletcher & Satz, 1979). Thus the long-standing debate as to whether visual factors play a significant role in reading disabilities has been complicated by the differences in methodological factors and the failure to distinguish between the measurement of temporal versus pattern-formation processes. In the following section an approach to vision that considers different mechanisms for the processing of temporal and pattern information is outlined.