A theoretical and experimental case for a visual deficit in specific reading disability

Abstract

We present three lines of evidence indicating a low-level visual deficit in a large percentage of specifically-disabled readers. This research is presented within the theoretical framework of spatial frequency analysis, in particular, the framework of transient and sustained subsystems.a. Measures of visible-persistence duration as a function of spatial frequency in normal and specifically-disabled readers show that disabled readers have a different pattern of temporal processing across spatial frequencies. These differences disappear when transient system activity is reduced.On measures of pattern-contrast sensitivity specifically-disabled readers are less sensitive than controls at low spatial frequencies, but equal or more sensitive at high spatial frequencies.On measures of temporal-contrast sensitivity disabled readers are less sensitive than controls at all flicker rates with the greatest differences being at the higher temporal frequencies.These three sources of evidence indicate that disabled readers have a deficient transient system.On the other hand, a fourth series of experiments investigated sustained system functioning in the two groups and failed to show any differences between them. It is argued that the existing confusion over visual deficits in disabled readers may be related to our findings of a transient but not a sustained system deficit. Further analyses indicate that these differences do not result from failing at reading, are present before reading instruction commences and occur in approximately 75% of subjects tested. An attempt is made to relate these findings to existing classifications of sub-types of specific reading disability. Some discussion of how a transient system deficit may influence the reading process is offered. b.c.Requests for reprints should be sent to

Visual motion sensitivity in dyslexia: evidence for temporal and energy integration deficits

“…Some psychophysical studies have failed to con®rm that such visual de®cits are associated with dyslexia ( [20,21,61], see also, [17] for review). Nevertheless most experimental evidence is consistent with the hypothesis that the M (or transient) pathway is a locus of their subtle visual impairments (for reviews see [29,30,56]). …”

“…[54]). Although de®cits in component language skills such as phonological awareness are recognised as important causes of poor reading [8,49,55], there is now a large amount of literature showing that de®cient visual processing skills are also associated with reading diculties (see [29,30,32,46,56] for review). In the laboratory, many developmental dyslexics are found to be less sensitive than controls to dynamic visual stimuli, especially those of low contrast, low luminance, low spatial frequencies, and high temporal frequencies [10,28,30,31,33±35].…”

Specific reading disability (dyslexia): what have we learned in the past four decades?

“…However, the transient system theory has some empirical support (Breitmeyer, 1989;Badcock & Lovegrove, 1981;Lehmkuhle, Garzia, Turner, Hash, & Baro, 1993;Lovegrove et al, 1986;Lovegrove, Garzia, & Nicholson, 1990;Martin & Lovegrove, 1984), as does the motion perception theory (Eden et al, 1996). Thus, both warrant further comment.…”

“…Thus, Lovegrove and his associates have shown that poor and normal readers process high and low spatial frequency grids differently. They also have different contrast sensitivity functions, such that the poor readers require greater luminosity than the normal readers for distinguishing low frequency grids (Badcock & Lovegrove, 1981;Lovegrove et al, 1986Lovegrove et al, , 1990Martin & Lovegrove, 1984). That dyslexics are subject to trace persistence has been inferred from such findings.…”

Visual information processing in dyslexic children

“…An irregular magnocellular system could reduce the visual sensitivity for moving or flickering stimuli (Cornelissen et al, 1998a) and therefore to interfere with lexical decision tasks (Cornelissen et al, 1998b) or the detection of small letters (Stein and Walsh, 1997) for example. Since the earliest studies (Lovegrove et al, 1980(Lovegrove et al, , 1982(Lovegrove et al, , 1986) sinusgratings have been one of the most popular experimental means. Depending on the spatial frequency (cycles of the bright and dark bars per degree visual angle) dyslexics showed a reduced sensitivity (Evans et al, 1994;Kubová et al, 1995) for motion detection.…”