Abstract
Previous research has suggested that people with dyslexia may have an impairment of inhibitory control. The oculomotor system is vulnerable to interference at various levels of the system, from high level cognitive control to peripheral neural pathways. Therefore, in this work we examined two forms of oculomotor inhibition and two forms of oculomotor interference at high and low levels of the control system. This study employed a prosaccade, antisaccade, and a recent distractor eye movement task (akin to a spatial negative priming) in order to explore high level cognitive control and the inhibition of a competing distractor. To explore low-level control we examined the frequency of microsaccades and post-saccade oscillations. The findings demonstrated that dyslexics have an impairment of volitional inhibitory control, reflected in the antisaccade task. In contrast, inhibitory control at the location of a competing distractor was equivalent in the dyslexic and non-dyslexic groups. There was no difference in the frequency of microsaccades between the two groups. However, the dyslexic group generated larger microsaccades prior to the target onset in the prosaccade and the antisaccade tasks.The groups did not differ in the frequency or in the morphology of the post-saccade oscillations. These findings reveal that the word reading and attentional difficulties of dyslexic readers cannot be attributed to an impairment in the inhibition of a visual distractor or interference from low-level oculomotor instability. We propose that the inhibitory impairment in dyslexia occurs at a higher cognitive level, perhaps in relation to the process of attentional disengagement.
Highlights
Skilled reading requires a combination of perceptual and phonological skills
In this work we focus on four potential sources of oculomotor interference and instability that would impede efficient visual processing and the accuracy of saccadic eye movements during reading: (1) Inhibitory control of an irrelevant saccade; (2) Accurate target selection in presence of a competing distractor; (3) The overexpression of microsaccades during periods of steady fixation (Bowers and Poletti, 2017); (4) Post-saccadic oscillations that might enhance the retinal slip or motion toward the end of a saccade
One influential theory of dyslexia claims that the disorder is caused by a sluggish attention system, that involves deficiencies in the inhibition of irrelevant sensorimotor control
Summary
Text is segmented into meaningful chunks for the recognition of familiar words which is translated into a phonological code (LaBerge and Samuels, 1974) This skill is crucially dependent on the fast and efficient ability to focus and shift visual attention rapidly across the relevant text, and to inhibit competing and irrelevant distractors. In this work we focus on four potential sources of oculomotor interference and instability that would impede efficient visual processing and the accuracy of saccadic eye movements during reading: (1) Inhibitory control of an irrelevant saccade (i.e., antisaccade); (2) Accurate target selection in presence of a competing distractor; (3) The overexpression of microsaccades during periods of steady fixation (Bowers and Poletti, 2017); (4) Post-saccadic oscillations that might enhance the retinal slip or motion (i.e., noise) toward the end of a saccade
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