Visual print tuning deficits in dyslexic adolescents under minimized phonological demands

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Abstract

The left ventral occipitotemporal cortex is reliably activated by visual orthographic stimulation and has repeatedly been found underactivated in developmental dyslexia. However, previous studies have made little effort to specifically probe orthographic processing while minimizing the need for higher-order reading related operations, especially phonological processing. Phonological deficits are well documented in dyslexia but may limit interpretations of ventral occipitotemporal underactivation as a primarily orthographic coding deficit, considering that different processing modes occur highly parallel. We therefore used a task that restricts higher-order processing to better isolate orthographic deficits. Thirteen dyslexic adolescents and twenty-two matched typical readers performed a low-level target detection task combined with rapidly presented stimuli of increasing similarity to real words during functional magnetic resonance imaging. The clear deviance found in impaired readers' left ventral occipitotemporal organization suggested deficits in print sensitivity at bottom-up processing stages that are largely independent of phonological operations. This finding elucidates print processing during a critical developmental transition from child- to adulthood and extends current accounts on left ventral occipitotemporal functionality.

Highlights

▸ Adolescent dyslexics studied at a critical developmental stage for fluent reading. ▸ A task that targets bottom-up print processing and minimizes phonological confounds. ▸ Typical readers’ ventral occipitotemporal cortex is tuned to letter processing. ▸ Dyslexic readers fail to show bottom-up tuning even without phonological challenge.

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