ABSTRACT
Eye movements latencies toward peripherally presented stimuli were measured in 10-year-old dyslexic and control children. Dyslexic subjects, previously found to be oversensitive to stimulation of the magnocellular channel, showed reduced latencies as compared to normally reading controls. An attention shifting task was also used which showed no group differences in latencies of eye movements. The data are discussed in terms of the hypothesis of magnocellular system alteration and attention dysfunction in dyslexia. Additionally, sex differences in eye movement latencies were found and are discussed.
Subject(s)
Attention/physiology , Dyslexia/physiopathology , Eye Movements/physiology , Reaction Time/physiology , Visual Pathways/physiology , Child , Female , Humans , Male , Multivariate Analysis , Psychological Theory , Sex FactorsABSTRACT
Dyslexic and control children were tested in a visuomotor attentional task, which provides independent measures of the alerting, orienting and conflict components of the attentional system. Our results show that dyslexics are impaired with respect to controls in the attentional conflict component (resolution of conflict of incongruent peripheral information), while the alerting and orienting components remain preserved. It excludes an overall attentional impairment and points to more specific attentional processing difficulty i.e. distributed attention strategy. Generally, results of dyslexic boys are within the range of the control group, while reaction times of dyslexic girls are significantly slower than that of all other groups.
Subject(s)
Attention Deficit Disorder with Hyperactivity/physiopathology , Dyslexia/physiopathology , Photic Stimulation/methods , Psychomotor Performance/physiology , Sex Characteristics , Analysis of Variance , Attention Deficit Disorder with Hyperactivity/psychology , Child , Dyslexia/psychology , Female , Humans , MaleABSTRACT
The hypothesis of a magnocellular channel deficit in dyslexia was tested. Subjects were 10-year-old dyslexics and normal readers. Psychophysical thresholds for luminance and chromatic contrasts were estimated using black and white and red and green sinusoidal gratings of various spatial frequencies, presented in static and dynamic conditions (drift and reversal). Significant group differences were found for luminance contrast, with a higher sensitivity in dyslexics. No group differences were obtained for chromatic contrast. High luminance contrast sensitivity correlated with low reading and writing skills. The typical finding of an increase contrast sensitivity to low spatial frequency gratings, due to their dynamic presentations, was absent in dyslexics. The results provide support for the magnocellular deficit hypothesis. The pattern of this deficit, however, is much more complex than that emerging from previous research.
