An Examination of Methods Used to Test the Visual Perceptual Deficit Hypothesis of Dyslexia

Abstract

Two methodological problems often arise in dyslexia research. The first problem concerns the validity of experimental measures and the related problem of interpreting null results. The second problem involves the effects of sampling from a disabled population if the disorder under investigation has multiple unknown origins. Both problems were illustrated by a discussion of research aimed at testing the visual perceptual deficit hypothesis of dyslexia. Many studies cited as evidence against this hypothesis suffer from one or both problems. Data are presented in support of the visual perceptual deficit hypothesis. The authors suggest that visual perceptual dysfunction may account for some forms of dyslexia. Visual perceptual deficits must be ruled out as an explanation for poor performance by dyslexic children on tasks using visual stimuli before "higher order* deficits in cognitive processing can be reasonably postulated.S tudies undertaken to determine the etiology of reading disabilities have produced evidence for and against different theories (see Benton 1975 for a review). This confusing picture results partly from difficult methodological problems affecting research in this field. Two problems will be discussed: (1) if a method adequately measures what it purports to measure and (2) how the interpretation of data is affected by a sampling of children who demonstrate a disorder of unknown and probably multiple origins

The evidence for a temporal processing deficit linked to dyslexia: A review

“…The conclusions drawn in studies such as that of Vellutino et al (1975) have been questioned by Gross and Rothenberg (1979), who cautioned against the premature and possibly erroneous rejection of a hypothesis, particularly when the hypothesis has been tested on such a heterogeneous group as dyslexics. Existing sequence-matching studies, although they may provide evidence for a phonemic deficit, generally do not enable us to determine whether a sequential or a temporal processing deficit (that may underlie the phonemic deficit) is also present.…”

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

“…Negative results have even been found on several perceptual tasks which appear to be closely related to tasks involved in reading (for example Katz & Wicklund, 1971). Even though some of these studies have been criticised on methodological grounds (Fletcher & Satz, 1979aGross & Rothenberg, 1979), it is unlikely that these criticisms would apply to all such studies. We will argue that SRDs may indeed have a low-level deficit and that many of these results may still be correct.…”

Visual Persistence and Information Pick-up in Learning Disabled Children

“…A slower, less efficient pick-up of information would result in a decrease in correct recognitions and, therefore, a decrease in the span of apprehension (similar to that observed for the LD boys by Mclntyre et al 1978). The efficacy of the pick-up of visual information has been assessed with a backward masking paradigm (Gross & Rothenberg 1979). This paradigm involves a target, which is briefly displayed, followed by a mask (a pattern of lines or dots) that impedes the identification of the target (especially if it is presented temporally close to the target offset).…”