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Matthieu Dubois, Sylviane Valdois; Visual span as a sensory bottleneck in learning to read. Journal of Vision 2010;10(7):952. doi: 10.1167/10.7.952.
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The visual span is the number of letters, arranged horizontally as in text, that can be recognized without moving the eyes. It represents a sensory bottom-up bottleneck that limits reading speed (Legge et al., 2007). In adult fluent readers, the visual span equals the uncrowded span, the number of characters that are not crowded. Reading rate is proportional to the uncrowded span (Pelli and Tillman, 2008). But what about learning to read? Developmental growth of the visual span accounts for 35-52% of the reading speed variability in english speaking children (Kwon et al., 2007). Here we investigate whether this relationship applies to French speaking children and to dyslexics.
In two age-matched groups of 10 dyslexic and 38 learning-to-read children (from 3rd to 7th grade), we estimate the visual span and reading rate. As predicted by the hypothesis, we find that visual span size and reading speed both linearly increase with chronological age in normal reading children. Congruently with the Kwon et al.'s (2007) results, a significant part of the control participants' reading speed was accounted for by their visual span size. Dyslexics had small visual spans and slow reading rate. In nearly half (4 of 10) of the dyslexic sample, reading slowness is accounted for by the visual span shrinkage. For the remaining dyslexic participants, additional factors are required to explain their slow reading speed.
Kwon, M., et al. (2007). Developmental changes in the visual span for reading. Vision Research, 47(22), 2889–900.
Legge, G. E., et al. (2007). The case for the visual span as a sensory bottleneck in reading. Journal of Vision, 7(2), 1–15.
Pelli, D. G., & Tillman, K. (2008). The uncrowded window of object recognition. Nature Neuroscience, 11(10), 1129–35.
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