The spacing words and pseudowords reading test: normative data to measure peripheral acquired dyslexia in the Italian adult population

Introduction Recent studies in right-brain-damaged patients with an acquired reading disorder have shown that omission and substitution errors in reading single words and pseudowords may result from two different mechanisms: the association of spatial neglect with altered eye movements (neglect dyslexia), which produces left-sided omissions, or an enhancement of a crowding phenomenon (crowding dyslexia), responsible for less lateralized substitutions. This study aims to provide normative data for the Spacing Words and Pseudowords (SWAP) reading test for the Italian population, a novel tool sensitive to identify specific visuo-perceptual and attentional deficits in patients with acquired peripheral dyslexia based on the modulatory effect of letter spacing. Methods The test was administered to 199 neurologically unimpaired Italian participants (86 males), with an average age of 57.3 years (range 20–90) and an average education of 14.1 years (range 5–28). An innovative scoring method based on the type and position of errors (letter-based) was proposed, and the effect of spacing condition on specific types of errors was investigated. Results Regression-based norms are provided for both word-based and letter-based errors. A significant effect of spacing on accuracy, with an increased number of errors in the spaced compared to the unspaced condition, was observed for substitutions and additions, but not for omissions. Furthermore, examples to illustrate the clinical application of the test in right-brain-damaged patients with acquired dyslexia are described. Discussion The SWAP reading test, provided with proper norms, may serve as a clinical tool to investigate visual-perceptual and attentional mechanisms involved in reading and possibly affected by brain damage, disentangling neglect dyslexia from crowding dyslexia.