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

Area of Science:

• Cognitive Neuroscience
• Experimental Psychology
• Neurology

Background:

• Previous research indicates initial letters hold a privileged role in visual word recognition.
• Attentional dyslexia studies show reduced errors for early letter transpositions.
• Posterior cortical atrophy (PCA) impairs visuospatial and attentional functions.

Purpose of the Study:

• To replicate and extend findings on the privileged role of initial letters in visual word recognition.
• To investigate this phenomenon in patients with posterior cortical atrophy (PCA).
• To assess the impact of visual orientation on early letter encoding.

Main Methods:

• Two PCA patients performed lexical decision tasks with five-letter words and nonwords.
• Nonwords were created by transposing adjacent letters (positions 1+2, 2+3, 3+4, 4+5) or matched controls.
• Stimuli were presented horizontally and vertically; tasks were repeated for robustness.

Main Results:

• Both PCA patients demonstrated significantly higher accuracy and lower response bias for 1+2 transposition nonwords.
• This early-letter advantage was consistent across test-retest sessions.
• The effect persisted regardless of stimulus orientation (horizontal vs. vertical).

Conclusions:

• PCA patients exhibit an orientation-invariant advantage for early letter encoding in visual word recognition.
• This suggests early letter processing is resilient and independent of visual orientation, even with attentional deficits.
• Findings support models where initial letters act as crucial anchor points in orthographic processing.