Sustained Attention as Measured by Reaction Time Variability Is a Strong Modulator for the P600, but Not the N400.

Area of Science:

• Cognitive Neuroscience
• Psycholinguistics
• Electrophysiology

Background:

• The functional significance of N400 and P600 event-related potential (ERP) components in language processing remains debated.
• A recent hypothesis suggests N400 reflects automaticity and P600 reflects attentional control in sentence comprehension.
• Controlled language processing relies on executive resources dependent on fluctuating sustained attention.

Purpose of the Study:

• To investigate whether P600 and N400 amplitudes are modulated by the level of sustained attention during sentence comprehension.
• To provide evidence for or against the automaticity vs. attentional control account of N400 and P600.

Main Methods:

• Reanalysis of existing EEG and behavioral data from a sentence processing task involving morphosyntactic and semantic violations.
• Quantification of sustained attention using the coefficient of variation of reaction times over time.
• Correlation analysis between ERP amplitudes (N400, P600) and measures of sustained attention.

Main Results:

• P600 amplitude was significantly larger during periods of high sustained attention (low reaction time variability).
• N400 amplitude did not show a significant relationship with varying levels of sustained attention.
• These findings indicate differential sensitivity of P600 and N400 to attentional states.

Conclusions:

• The P600 component's sensitivity to sustained attention supports its role in controlled aspects of sentence comprehension.
• The N400 component's lack of sensitivity to sustained attention aligns with its proposed role in automatic language processing.
• This study offers independent electrophysiological evidence for distinct automatic and controlled processing mechanisms reflected by N400 and P600, respectively.