Visual perception in dyslexia is limited by sub-optimal scale selection

Johnston, Richard; Pitchford, Nicola J.; Roach, Neil W.; Ledgeway, Timothy

Abstract

Readers with dyslexia are purported to have a selective visual impairment but the underlying nature of the deficit remains elusive. Here, we used a combination of behavioural psychophysics and biologically-motivated computational modeling to investigate if this deficit extends to object segmentation, a process implicated in visual word form recognition. Thirty-eight adults with a wide range of reading abilities were shown random-dot displays spatially divided into horizontal segments. Adjacent segments contained either local motion signals in opposing directions or analogous static form cues depicting orthogonal orientations. Participants had to discriminate these segmented patterns from stimuli containing identical motion or form cues that were spatially intermingled. Results showed participants were unable to perform the motion or form task reliably when segment size was smaller than a spatial resolution (acuity) limit that was independent of reading skill. Coherence thresholds decreased as segment size increased, but for the motion task the rate of improvement was shallower for readers with dyslexia and the segment size where performance became asymptotic was larger. This suggests that segmentation is impaired in readers with dyslexia but only on tasks containing motion information. We interpret these findings within a novel framework in which the mechanisms underlying scale selection are impaired in developmental dyslexia.

Citation

Johnston, R., Pitchford, N. J., Roach, N. W., & Ledgeway, T. (in press). Visual perception in dyslexia is limited by sub-optimal scale selection. Scientific Reports, 7, Article 6593. https://doi.org/10.1038/s41598-017-06967-6

• Journal Article Type: Article
• Acceptance Date: Jun 26, 2017
• Online Publication Date: Jul 26, 2017
• Deposit Date: Jul 27, 2017
• Publicly Available Date: Jul 27, 2017
• Journal: Scientific Reports
• Electronic ISSN: 2045-2322
• Publisher: Nature Publishing Group
• Peer Reviewed: Peer Reviewed
• Volume: 7
• Article Number: 6593
• DOI: https://doi.org/10.1038/s41598-017-06967-6
• Keywords: Dyslexia, Poor readers, Segmentation, Motion, Form, Scale selection
• Public URL: https://nottingham-repository.worktribe.com/output/874485
• Publisher URL: https://www.nature.com/articles/s41598-017-06967-6
• Contract Date: Jul 27, 2017