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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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