Understanding dyslexia by measuring eye-movements during reading.

Abstract

Dyslexia has been causally linked to both phonological deficits (Snowling, 2000) and difficulties in allocating attention (Valdois, Bosse, & Tainturier, 2004; Vidyasagar, 1999; Whitney & Cornelissen, 2005), both of which are utilised during parafoveal processing (Schotter, Angele, & Rayner, 2012). Whilst dyslexic readers have been found to display disruption in oculomotor control relative to skilled readers (Kirkby, Webster, Blythe, & Liversedge, 2008), there is a lack of research examining dyslexic parafoveal processing during reading. The experiments presented throughout this thesis examined whether parafoveal processing is less efficient for dyslexic readers compared to non-dyslexic readers (Jones, Ashby, & Branigan, 2013), and, explored the nature of dyslexic eye movement behaviour by including both a chronological- age and a reading-age matched control group. In three silent sentence-reading experiments, eye movements were recorded from dyslexic and non-dyslexic readers. Using the boundary paradigm (Rayner, 1975), parafoveal previews were either manipulated orthographically or phonologically. The results of these experiments indicated that readers with dyslexia gain parafoveal preview benefit during reading. Dyslexic children and adults demonstrated orthographic parafoveal preview benefits and encoded letter identity independently of letter position. Dyslexic readers did, however, show a specific dyslexic deficit in which they required a greater dependence on letter position information for lexical activation. When examining phonological preview benefits, neither dyslexic nor non-dyslexic readers showed a significant benefit for phonological pre-processing. All three experiments provided evidence that dyslexic readers demonstrated differential eye movement patterns to non-dyslexic readers. Dyslexic readers required additional fixations, longer gaze durations and total reading times even when compared to non-dyslexic readers matched on reading age. Taken together, the results indicate that dyslexic eye movement behaviour is not purely indicative of their reduced reading skill and is due to a specific dyslexic reading deficit. These findings are consistent with both phonological and attention deficit theories of dyslexia and indicate that dyslexic readers rely upon a serial sublexical grapheme–phoneme conversion method of reading (Hawelka, Gagl, & Wimmer, 2010).