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Dyslexia: testing the magnocellular and attentional deficits hypothesis
The study aimed at verifying the hypothesis that dyslexia may result from magnocellular channel deficit. We based on the
assumption that the magnocellular channel is
color-blind and at the same time it is highly sensitive to luminance
contrast and to movement. In the study we tested colour
and luminance sensitivity to stationary and moving grating
(black-and-white and red-and-green) of different spatial frequency. The
pattern of results suggested that in dyslexics the colour
sensitivity is comparable to, whereas contrast sensitivity is higher than
in normal readers especially in those conditions which engage mostly the magnocellular pathway. In another study we
investigated of the latencies of eye movements directed to peripheral
stimuli in the same subjects. The study showed faster RTs
as compared to control subjects in condition where they were not informed
about the location of the stimulus. This finding is in agreement with the
previous data showing oversensitivity of magnocellular
channel in dyslexia.
The latest study
was performed in cooperation with University of Sevilla. Dyslexic and control children were tested in a
visuomotor attentional
task, which provide independent measures of the alerting, orienting and
executive components of attention. Our results showed that dyslexics were
impaired with respect to controls in the attentional
executive component (resolution of conflict in incongruent peripheral
information), while the alerting and orienting components remained
unaffected.
Bednarek D.B, Tarnowski A, Grabowska
A. Latencies of stimulus-driven
eye movements are shorter in dyslexic subjects. Brain and Cognition,
2005
Grabowska A, Bednarek D. Różnice płciowe w dysleksji. W:
A. Grabowska i K. Rymarczyk
(Red). Dysleksja: od badań mózgu do praktyki. Instytut Biologii
Doświadczalnej im. M. Nenckiego PAN, Warszawa,
217-243, 2004
Grabowska A, Rymarczyk K. (Red). Dysleksja: od badań mózgu do praktyki.
Instytut Biologii Doświadczalnej im. M. Nenckiego
PAN, Warszawa, 2004
Bednarek D, Quintero-Gallego E, Saldańa D, García I, Grabowska A, Gómez C.M. Attentional deficit in dyslexia: a general or specific
impairment? NeuroReport, 15(11):
1787-1790,, 2004
Grabowska A, Giuliano A. In
aid of dyslexia. European Association for International
Education Forum, 5(3): 20, 2003
Bednarek D, Grabowska A. Luminance
and chromatic contrast sensitivity in dyslexia: The magnocellular
deficit hypothesis revisited. NeuroReport, 13(18):
2521-2525, 2002
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