Inter-letter spacing and eye movements in typical developing readers and dyslexics.
Résumé
Most studies today agree about the link between visual-attention and oculomotor control during reading: attention seems to affect saccadic programming, that is, the position where the eyes land in a word. In a previous eye movement study (Bellocchi & Ducrot, submitted), it has been showed that fifth grade typical reading children take the direction of attentional scanning (left-to-right) into account, which results in asymmetrical landing-position pattern: this mechanism depends on the discreteness of the stimulus and interestingly, it is less irrepressible in lower reading level children and in children with reading disability. Furthermore, some studies have demonstrated that increasing inter-letter spacing or inter-word spacing improves the legibility of texts, especially for dyslexic children (e.g. Zorzi et al., 2012): is this improvement linked to a bigger inter-letter saliency which produces, in turn, a more precise saccade programming? To explore this question we assessed the eye movements of three groups of children: dyslexic readers, unimpaired reading-level controls, and unimpaired chronological-age controls, using a lateralized bisection task (participants were asked to move their eyes to a position they thought to be the middle of the stimulus) and a lexical decision task. The type of stimulus – bisection task (words vs. non-linguistic stimuli), LDT (words vs. pseudowords) and crowding (spaced vs. unspaced) - in combination with the stimulus presentation side (left vs. right) were manipulated. Main results showed that saccade computation seems to be modulated by crowding, stimulus presentation side and reading level. Results are discussed with respect to current models of oculomotor control in typical and defective reading.
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