The First Shall Be First: Letter-Position Coding and Spatial Invariance in Two Cases of Attentional Dyslexia.

Abstract

Background/Objectives: Previous research has demonstrated that the initial letters of a word likely play a privileged role in visual word recognition, such that reading and visual recognition errors reflecting changes in this position are much less likely. For example, prior case studies of attentional dyslexia reported that participants were most accurate at rejecting nonwords formed by transposing a word's first two letters (e.g., WONER from OWNER) compared to transpositions in later positions. The current study aimed to replicate and extend this finding in patients with posterior cortical atrophy (PCA), a neurodegenerative condition associated with visuospatial and attentional impairments. Methods: Two PCA patients completed lexical decision tasks involving five-letter real words and nonwords created either by transposing adjacent letters (in positions 1 + 2, 2 + 3, 3 + 4, or 4 + 5) or using matched nonword controls. To assess robustness, tasks were repeated across test-retest sessions. Stimuli were presented in both canonical horizontal and non-canonical vertical (marquee) formats. Accuracy, response bias, and sensitivity (d') were estimated, with 95% confidence intervals derived from a nonparametric bootstrap procedure. Within-case logistic regressions were also conducted to illustrate the findings. Results: Both patients showed significantly higher accuracy and lower response bias for 1 + 2 transposition nonwords relative to other positions. This early-letter advantage persisted across test-retest observations and was maintained when words were presented in the vertical format, suggesting orientation-invariant effects. The bootstrap and regression analyses provided convergent support for these results. Conclusions: The findings provide novel evidence in PCA that the encoding of early letter positions operates independently of visual orientation and persists despite attentional deficits. This supports models in which the initial letters serve as a key anchor point in orthographic processing, highlighting the privileged and resilient status of early letter encoding in visual word recognition.