The N400 in typical and atypical readers: A systematic review and a meta-analysis

The N400 in typical and atypical readers: A systematic review and a meta-analysis

First Author: Badriah Basma -- McGill University
Additional authors/chairs: 
Armando Bertone
Keywords: Reading disability, Reading comprehension, EEG, ERP, Meta-analysis
Abstract / Summary: 

Purpose
A reading disability (RD) results from the inability to decode words and may manifest itself as a deficit in reading comprehension. At a neural level, research suggests that a deficiency in the brain process results in the atypical development of word-level and text level (lexical and semantic tasks). To investigate how the brain processes languages in real-time, researchers use Event-Related potentials (ERPs) that measure real-time processes in milliseconds. The N400 is a delicate ERP waveform that is sensitive to the lexico-semantic aspect of language and able to detect how the brain processes language and comprehension. The purpose of this systematic review and meta-analysis is to inquire about the difference in the N400 amplitude between typical and atypical readers to better understand how the brain processes language and comprehension in real-time, specifically in individuals with RD.
Method
We ran a tertiary systematic review to evaluate all the systematic reviews and meta-analysis on the N400 in individuals with RD. No reviews were found. The second part of the paper focused on all the N400 studies that included typical and atypical readers. Nineteen studies were included in the meta-analysis to explore the standard difference in mean in the N400 amplitude between typical and atypical readers.
Results
The analysis showed no strong evidence of publication bias and a Hedge's ( g=0.76, p = 0.00). Interestingly, this effect was moderated by the ERP modality, whereby studies that used visual ERP modality were significant with a large (g = 0.82, p< 0.001). Yet studies that used auditory modality had a medium effect size of (g = 0.66, p< 0.001).
Conclusion
Typical readers showed normal N400 amplitude while all individuals with RD had an aberrant N400 that is influenced by auditory and visual task modality. The anomalous N400 could be due not only to phonological processing deficits, but orthographic and morphological as well.