Acquired crowding dyslexia: A peripheral reading deficit other than neglect dyslexia.

Objectives: Crowding refers to the phenomenon whereby small visual objects above the acuity threshold are detected but unrecognizable when surrounded by nearby stimuli. It affects reading in healthy individuals and can be enhanced in reading impairments. By increasing the interletter space, crowding decreases. Previous evidence on patients with unilateral spatial neglect (USN) and peripheral dyslexia has shown a dissociation in sensitivity to spacing manipulation between those who mainly produced omissions and those characterized by substitutions in reading. Here, we wanted to verify the hypothesis that the reading impairment mainly characterized by substitutions is dissociated from USN, unlike the one characterized by omissions.

Method: In a retrospective study, we collected 38 right-brain-damaged patients, 21 with USN. We analyzed the number and types of errors in reading single words and pseudowords, spaced and unspaced, comparing patients with and without USN.

Results: USN patients showed significantly more omissions than patients without USN and increased omissions with letter spacing. Substitutions were more frequent in USN patients but did not increase with spacing. Performance of patients mainly characterized by substitutions revealed a reduction of errors with spaced pseudowords and a double dissociation from USN. Lesion overlap analysis suggested that the two deficits could depend on different components of visuospatial attention networks.

Conclusions: We claim that proper neglect dyslexia is characterized by omission errors and has USN as a necessary mechanism, even if not sufficient. Conversely, acquired crowding dyslexia is a different reading deficit, characterized by substitutions due to an enhanced crowding phenomenon, independent of USN. (PsycInfo Database Record (c) 2025 APA, all rights reserved).