Separating the visual sentence N400 effect from the P400 sequential expectancy effect: cognitive and neuroanatomical...

Area of Science:

• Cognitive Neuroscience
• Psycholinguistics
• Event-Related Potentials (ERPs)

Background:

• The N400 event-related potential (ERP) component reflects semantic processing and is amplified by unexpected sentence endings.
• Previous research suggested a distinct Cz-centered P400 (P400cz) alongside the classic Pz-centered N400 (N400pz) in response to semantic congruity.
• The precise neural sources and functional roles of these potential components remain under investigation.

Purpose of the Study:

• To investigate the presence and characteristics of the P400cz component during visual sentence processing.
• To compare the sensitivity of the P400cz and N400pz to semantic congruity and cloze probability.
• To explore the potential neural sources of the N400pz and P400cz.

Main Methods:

• Visual presentation of sentences, one word at a time, with half ending in semantically incongruent completions.
• High-density 129-channel electroencephalography (EEG) recording from 26 participants.
• Temporo-spatial principal components analysis (PCA) and item averaging to analyze event-related potentials.

Main Results:

• The presence of the P400cz component was confirmed.
• The P400cz demonstrated greater sensitivity to semantic congruity and slightly higher sensitivity to cloze probability compared to the N400pz.
• Findings support the separation of the N400 semantic effect into distinct N400pz and P400cz components.

Conclusions:

• The results confirm the P400cz as a distinct ERP component sensitive to semantic processing.
• The N400pz likely originates from the bilateral anterior medial temporal lobe (AMTL), reflecting semantic processing.
• The P400cz may originate from the medial parietal region, potentially reflecting a general sequential expectancy system.