Too wide or too narrow? Evaluating accessibility recommendations for inter-letter and inter-word spacing on digital reading performance and user experience

Digital accessibility guidelines increasingly shape the design of online text, yet some widely adopted typographic recommendations remain weakly supported in the general adult population. One such case concerns the minimum inter-letter and inter-word spacing values recommended by the Web Content Accessibility Guidelines (WCAG). The present Registered Report will examine whether WCAG spacing improves digital reading performance and user experience relative to default and enlarged spacing. Using a 3 × 3 within-subject design, the study will manipulate inter-letter spacing (default, WCAG-compliant, enlarged) and inter-word spacing (default, WCAG-compliant, enlarged) during a silent sentence-reading task. Objective outcomes will include comprehension accuracy and reading time, whereas subjective outcomes will include perceived difficulty, aesthetics, and spacing preference. Digital reading exposure and working memory will also be assessed as control variables. A sample of 107 adults will be recruited online via Prolific. Confirmatory analyses will consist of repeated-measures analyses of variance and preregistered planned contrasts comparing WCAG, default, and enlarged spacing conditions. It is hypothesised that WCAG-compliant spacing will yield better performance and more favourable subjective evaluations than default spacing, whereas enlarged spacing is expected to be comparable to, but not better than, WCAG-compliant spacing. By directly testing spacing thresholds that inform accessibility standards and public policy, this study aims to provide empirical evidence on whether current recommendations optimise reading performance and user experience in the general adult population.