N400/P600 Analysis
Event-Related Potential (ERP) Component Analysis: N400 and P600 · Also known as: ERP Analysis, Neurophysiological Semantics
N400/P600 Analysis is a neurocognitive method using electroencephalography (EEG) to measure event-related potentials (ERPs) that reflect brain responses to linguistic stimuli. The N400 component (a negative deflection at 400 ms) indexes semantic processing and surprise; the P600 component (a positive deflection at 600 ms) reflects syntactic processing and reanalysis. Discovered by Marta Kutas and Steven Hillyard in 1980, these components reveal the neural basis of language comprehension in real time.
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When to use it
Use N400/P600 analysis to investigate the neural basis of language comprehension, to determine whether a linguistic contrast engages semantic or syntactic processing, or to measure online language processing at high temporal resolution (millisecond level). ERP is especially useful for studying implicit processing, for revealing when violations are detected, and for comparing patient groups with normal readers.
Strengths & limitations
- Provides millisecond-level temporal resolution of neural processing, revealing exactly when semantic and syntactic violations are detected.
- Dissociates semantic (N400) from syntactic (P600) processing, answering which linguistic system is engaged.
- Captures implicit, automatic processing: no conscious judgment or response required, reducing potential confounds.
- Portable and relatively inexpensive compared to fMRI; allows study of diverse populations and real-time interactive settings.
- Poor spatial resolution: EEG reflects summation of neural activity from broad brain regions; pinpointing which brain structures are active is difficult.
- Requires careful experimental design and large sample sizes to achieve adequate signal-to-noise ratio (typical N=30-50 participants).
- Interpretation of components is sometimes ambiguous: other cognitive processes (attention, memory retrieval) can modulate N400 and P600.
- Substantial cross-subject variability in ERP waveforms requires standardized preprocessing and statistical methods.
Frequently asked
What does the N400 measure, and why is it called 'N400'?
The N400 is a negative (N) deflection in the ERP waveform peaking around 400 milliseconds (ms) after stimulus onset. It indexes semantic integration difficulty: unexpected or semantically incongruent words elicit larger N400s than expected, semantically congruent words. N400 reflects the effort or surprise involved in integrating a word's meaning with the surrounding context.
What is the difference between N400 and P600?
N400 (negative, ~400 ms) primarily reflects semantic/lexical processing; it is larger for semantically incongruent or unexpected words. P600 (positive, ~600 ms) primarily reflects syntactic processing and reanalysis; it appears following grammatical violations, garden-path sentences, or unexpected syntactic structures. They dissociate: a sentence can be grammatical but semantically odd (large N400, small P600) or syntactically anomalous but semantically coherent (small N400, large P600).
How many participants do I need for an ERP study?
Typical studies use 25-50 participants. The sample size depends on the effect size (how large the N400 or P600 difference is) and the number of trials per condition (more trials per condition allow smaller samples). Conduct a power analysis based on previous research to estimate required N. Larger samples increase reliability; smaller samples increase risk of non-replication.
Can ERP distinguish different types of semantic violations?
Yes, to some degree. Different semantic violations (word association, semantic field violations) can produce different N400 amplitudes and distributions. However, N400 is not finely selective; it is hard to use N400 alone to distinguish between specific types of meaning-related processes. Combine ERP with other methods (eye-tracking, comprehension measures) for a fuller picture.
Sources
- Kutas, M., & Hillyard, S. A. (1980). Reading senseless sentences: Brain potentials reflect semantic incongruity. Science, 207(4427), 203-205. DOI: 10.1126/science.7350657 ↗
- Osterhout, L., & Holcomb, P. J. (1992). Event-related brain potentials elicited by syntactic anomaly. Journal of Memory and Language, 31(6), 785-806. DOI: 10.1016/0749-596X(92)90039-Z ↗
- Luck, S. J. (2014). An Introduction to the Event-Related Potential Technique (2nd ed.). Cambridge, MA: MIT Press. link ↗
How to cite this page
ScholarGate. (2026, June 3). Event-Related Potential (ERP) Component Analysis: N400 and P600. ScholarGate. https://scholargate.app/en/linguistics/n400-p600-analysis