CHILDREN AFFECTED BY DEVELOPMENTAL DYSLEXIA SHOW REDUCED SENSITIVITY TO VISUAL MOTION ILLUSIONS

  • Andrea Facoetti
  • Enrico Giora
  • Luca Ronconi
  • Milena Ruffino
  • Simone Gori

Abstract

Although developmental dyslexia is often described in terms of selective phonological deficit, visual Magnocellular-Dorsal (M-D) deficit hypothesis gains an increasing consent, even if it remains a controversial theory. Several experimental data supporting the M-D deficit hypothesis, indeed, can also be interpreted as a consequence of a perceptual noise exclusion deficit. In our psychophysical experiments, we measured sensitivity for two visual motion illusions proved to involve specifically the M-D pathway. The results show that dyslexic group differed, in comparison to the control group, in perceiving both illusions. Specifically, dyslexics needed more luminance contrast to perceive the motion illusions, although contrast sensitivity for these specific stimuli did not differed between the two groups. These results are the first supporting the M-D deficit hypothesis in dyslexia by measuring sensitivity to visual motion illusion, without involving any perceptual noise exclusion mechanism.

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