An investigation into the relationship between low-level visual function and reading experience

Phonological impairments are strongly associated with reading difficulties (RD) in an opaque orthography such as English (Vellutino et al., 2004). However, there is much evidence for visual deficits in RD. Theories range from those related to a magnocellular deficit, inattention, enhanced crowding and hyperactivity of sustained pathway processing (Dain et al., 2008; Roach and Hogben, 2008; Martelli et al., 2009; Laycock et al., 2012). However, much conflicting support for these theories exists. In this study, the relatively less intensively researched area, of peripheral visual sensory processing, of participants with RD was explored. All participants answered a vision questionnaire and performed the comparative rate of character recognition test (CREST) (Griffiths, personal communication). They were all assessed for optometric abnormalities. Subsequently, their spatiotemporal achromatic and chromatic contrast sensitivities (033) were measured. Gabor patches of varying spatial frequency (SF); 0.3, 1 and 3 cycles per degree (cpd), and colour (achromatic, red-green and blue-yellow) were used. Achromatic and chromatic contrast thresholds were determined using a 2-alternative forced choice procedure along a 3-down, 1-up staircase paradigm. Stimuli were presented centrally and 10° peripherally. Peripheral flicker achromatic (F(1,19) = 4.841, p = 0.040), red-green (F(1,19) = 6.333, p = 0.021) and blue-yellow (F(1,19) = 5.822, p = 0.026) CSs were significantly attenuated in those with RD as calculated using ANOVA. Peripheral static achromatic CSs (F(1,19) = 10.120, p = 0.005) and central flicker blue-yellow CSs (F(1,19) = 5.815, p = 0.026) were similarly reduced. Peripheral static red-green (F(1,19) = 3.211, p 0.089) and blue-yellow CSs (F(1,19) = 4.287, p = 0.052) were significantly reduced if using a less stringent significance level of 0.1. A significant interaction between reading difficulty and retinal eccentricity was found in an overall ANOVA, F(1, 19), p<0.05. The general finding of this study was a peripheral vision defect in those with RD. A peripheral vision deficit may align the conflicting evidence of visual sensory deficits in RD.