ABSTRACT
The contribution of M(y)-cell activity within a framework of a magnocellular-deficit theory of dyslexia is currently unknown. Twenty-one dyslexic readers and 19 control readers were compared on their threshold detection for the frequency doubling illusion - an index of M(y)-cell activity, coherent motion, and a visual acuity task. The dyslexic group performed more poorly on detection of the frequency doubling illusion and coherent motion compared to the control group, but both groups performed comparably on the visual acuity task. The results from this study indicate that if a magno deficit exists in dyslexia, it may originate at a retinal level at least partly mediated by M(y)-cell abnormalities.
Subject(s)
Dyslexia/physiopathology , Optical Illusions , Visual Pathways/physiology , Case-Control Studies , Child , Color Perception/physiology , Contrast Sensitivity/physiology , Humans , Motion Perception/physiology , PsychophysicsABSTRACT
Metacontrast and apparent motion experiments designed to utilize transient system resources were adopted to investigate the proposal that transient system activity is differentially influenced by different colored stimuli. The results generally showed no effect of color on transient system activity in either adults or children. However, the predicted pattern of results was demonstrated when contrast rather than color was manipulated in a final metacontrast experiment. We discuss the tenuousness of the proposal that color differentially influences transient activity, exploring its physiological implications and its durability as a theory of transient activity regarding reading-disability research.
Subject(s)
Attention , Color Perception , Dyslexia/psychology , Adult , Child , Contrast Sensitivity , Discrimination Learning , Humans , Motion Perception , Perceptual Masking , Psychophysics , Remedial TeachingABSTRACT
We tested the hypothesis that in a cluttered visual scene, the magnocellular (M) pathway is crucial for focusing attention serially on the objects in the field. Since developmental dyslexia is commonly associated with an M pathway deficit, we compared reading impaired children and age-matched normal readers in a search task that required the detection of a target defined by the conjunction of two features, namely form and colour, that are processed by the parvocellular dominated ventral neocortical stream. The dyslexic group's performance was significantly poorer than the controls when there were a large number of distractor items. The scheme of selective attention proposed from these results provides a neural mechanism that underlies reading and explains the pathophysiology of dyslexia.