The effect of print size on reading speed in dyslexia

Abstract

This article details a study which predicted that across a wide range of print sizes dyslexic reading would follow the same curve shape as skilled reading, with constant reading rates across large print sizes and a sharp decline in reading rates below a critical print size. It also predicted that dyslexic readers would require larger critical print sizes to attain their maximum reading speeds, following the letter position coding deficit hypothesis. Reading speed was measured across twelve print sizes ranging from Snellen equivalents of 20/12 to 20/200 letter sizes for a group of dyslexic readers in Grades 2 to 4 (aged 7 to 10 years), and for non-dyslexic readers in Grades 1 to 3 (aged 6 to 8 years). The groups were equated for word reading ability. Results confirmed that reading rate-by-print size curves followed the same two-limbed shape for dyslexic and non-dyslexic readers. Dyslexic reading curves showed higher critical print sizes and shallower reading rate-by-print size slopes below the critical print size, consistent with the hypothesis of a letter-position coding deficit. Non-dyslexic reading curves also showed a decrease of critical print size with age. A developmental lag model of dyslexic reading does not account for the results, since the regression of critical print size on maximum reading rate differed between groups.Developmental dyslexia, a learning disability specific to reading, affects an estimated 5% of children in school. Reading requires processing of both the visual information from the page and the linguistic information that the print represents. Over a century of research on causal factors in developmental dyslexia has emphasised either one or the other of these processes, beginning with theories of visual causation. Morgan (1896) coined the inability to read in children as 'congenital word blindness ', while Orton (1928) described the phenomenon of 'strephosymbolia' (twisted symbols), where children could read mirror-image writing more easily. The current view of dyslexia holds that reading failure is caused by a linguistic deficit in coding phonemes (individual speech sounds) within words, and thereby in accessing and manipulating these phonemic codes as required on a wide range of tasks (phonological processing) (Snowling, 2000). This view holds that a phonological processing deficit impedes a child's ability to develop phoneme awareness, to learn grapheme-phoneme correspondence rules, and to decode words (Liberman et al., 1974;Stanovich & Siegel, 1994). The theory accounts for many cases of developmental dyslexia, but there are individuals with dyslexia who do not demonstrate a severe phonological deficit (Wolf & Bowers, 1999;Lovett, Steinbach & Frijters, 2000). Also, remediation programmes aimed at training phonological skills are often but not entirely successful (Lyon & Moats, 1997;Torgesen, 2000). This suggests a need for alternative or additional accounts of causal factors in dyslexia. Recent evidence shows that subtle impairments in visual processing characterise some...

Increasing interletter spacing facilitates encoding of words

“…On the one hand, very large interletter spacings hinder the perceptual integrity of the whole word (e.g., as in ) and (unsurprisingly) produce longer word identification times-indeed, this manipulation has been employed as a way to degrade words (e.g., see Cohen, Dehaene, Vinckier, Jobert, & Montavont, 2008). But on the other hand-and more importantly for the present purposes-small increases in interletter spacing (relative to the default settings; compare vs. ) do not destroy the integrity of the written word but do produce two potential benefits: fewer "crowding" effects (i.e., less interference from the neighboring letters; see Bouma, 1970;O'Brien, Mansfield, & Legge, 2005) and a more accurate process of letter position coding (see Davis, 2010;Gomez, Ratcliff, & Perea, 2008).…”

Extra-large letter spacing improves reading in dyslexia

“…* However, very little research has investigated the potential effects of such manipulations (12,13). Here, we pursue this approach, which is motivated by behavioral evidence showing that dyslexics are abnormally affected by crowding (14)(15)(16)(17), a perceptual phenomenon with detrimental effects on letter recognition that is modulated by the spacing between letters (18,19).…”

The Project “Interactive Topography of Dante’s Inferno”. Transfer of Knowledge and Design of Didactic Tools

“…The font size ranges from 16 px to 33 px (therefore on the monitor we used-1366 × 768 px, 15 inchesthe x-height measures about 2 mm), which are bigger sizes than the ones reported in literature as critical for reading [25,26], even considering the users' self underestimation of the critical threshold for the optimal reading performance [25].…”