Relating visual crowding, visual span and reading in dyslexia

Relating visual crowding, visual span and reading in dyslexia

First Author: Nilsu Atilgan -- University of Minnesota
Additional authors/chairs: 
Sheng He; Gordon E. Legge
Keywords: Dyslexia, Visual perception, visual attention, visual span, visual crowding
Abstract / Summary: 

Purpose: Despite many studies investigating visual crowding in dyslexia, the relationships between crowding, reading and visual span (the number of text letters that can be recognized accurately without eye movements) are not well understood. In this study, we aimed to answer the following questions: 1) Do individuals with dyslexia suffer from more crowding than typical readers? 2) If yes, is the excess crowding restricted to letter stimuli? 3) Do visual span profiles differ between these two groups?
Method: We conducted two psychophysics experiments (crowding and visual span) with the same subjects including both individuals with and without dyslexia. In the crowding experiments, three different visual stimuli (i.e. letters, unique symbols, gratings) were used to see if linguistic content plays a role in the crowding effect. We measured participants’ critical spacing (where crowding effect decreases permitting identification performance to exceed to a criterion level). In the visual span experiment, we tested each participants’ visual span with single letters and trigrams (both full and partial reports, letters presented at a range of distances from fixation).
Results: Critical spacing values showed variations in the performance of participants with dyslexia. While some participants showed substantially larger crowding effect, some participants demonstrated similar performance as typical readers. The stimulus type did not have a significant effect on performance. Our results also showed that individuals with dyslexia have narrower visual span profiles. Previous studies have shown a correlation between size of the visual span and reading speed.
Conclusions: The current study, first time in the literature, shows that adults with dyslexia differ in their visual span profiles from typical readers. Our results also indicate that individuals with dyslexia show varied effects of crowding, implying nonuniformity in the dyslexia population in peripheral visual perception