Where dyslexics look first in a stimulus: The influence of visual and linguistic factors on saccade computation
Résumé
In addition to appropriate phonological abilities, learning to read requires an accurate visual analysis that allows for precise decoding of the written words. The present study examines the possibility that a disturbance in the early processing of visuo-perceptual information needed to guide eye movements may be an important factor in dyslexia. We assessed the eye movements of three groups of children: dyslexic readers, unimpaired reading-level controls (RL-controls), and unimpaired chronological-age controls (CA-controls). Participants were asked to perform a lexical-decision task on stimuli presented either left or right of an initial fixation point. The most important result of this experiment was a saccade-size asymmetry between left and right presentations for all three groups of participants, although the asymmetry obtained for the dyslexics and RL-controls was less pronounced than for the CA-controls. The dyslexic readers did not differ from the RL-controls on gaze duration or lexical-decision time, and both of these groups exhibited sensitivity to word frequency and lexicality. The only substantial difference between the dyslexics and the others occurred when they had to process pseudowords in the right visual field, where their gaze duration, lexical-decision time, and second-saccade landing position deviated markedly. The theoretical consequences of these results are discussed.