Surface errors without semantic impairment in acquired dyslexia: a voxel-based lesion-symptom mapping study

Area of Science:

• Neuroscience
• Cognitive Psychology
• Linguistics

Background:

• Surface dyslexia involves difficulty with irregularly spelled words, indicating issues with lexical-semantic mediation of phonological retrieval.
• Patients often exhibit 'regularization' errors, mispronouncing irregular words by applying regular spelling-sound rules, suggesting over-reliance on grapheme-phoneme correspondences.

Purpose of the Study:

• To investigate the neuroanatomical basis of regularization errors in patients with surface dyslexia.
• To determine if these errors are linked to semantic deficits or a distinct processing mechanism.

Main Methods:

• Voxel-based lesion-symptom mapping was used in 45 patients with left hemisphere chronic stroke.
• The study analyzed the correlation between the rate of regularization errors and lesion location.
• Semantic comprehension was assessed, and its relationship with regularization errors was examined.

Main Results:

• A significant positive correlation was found between regularization errors and damage to the posterior left middle temporal gyrus.
• Mild semantic deficits were observed but did not correlate with regularization errors.
• The lesion site for regularization errors was distinct from the white matter area associated with semantic deficits.

Conclusions:

• Surface errors in this patient group are not directly related to semantic deficits.
• The findings suggest a post-semantic mechanism for producing surface errors, potentially involving an inability to link semantic and phonological representations.
• The posterior middle temporal gyrus may play a crucial role in mediating this semantic-phonological link.