Systematic Variability in Language Related ERP Morphology
Shannon McKnight1, Donald Bell-Souder1, Akira Miyake1, Albert Kim1; 1University of Colorado Boulder
ERP studies of language comprehension widely observe that semantic anomaly modulates a central-parietal negative-going wave ~300-500 ms after word-onset (N400), while syntactic anomalies elicit a positive-going wave ~500-800 ms after word-onset (P600). These ERPs illuminate neurocognitive processes, but their interpretation is complicated by variability in EEG activity often ignored in ERP studies. We characterized the consistency and variability of language processing ERPs in a large group of 159 participants, by repeatedly re-sampling into smaller groups of 20, 30, and 40 participants, simulating different runs of the same experiment. We observed classic N400 and P600 effects but also substantial variability in the morphology and antecedent conditions of those ERPs across samples. Semantic anomaly N400s sometimes extended beyond the classic time window to ~800-900 ms after word-onset. Across samples, extended N400s predicted smaller syntactic anomaly P600s, suggesting a tradeoff between N400 and P600 generators across sentence types. Syntactic anomalies sometimes elicited a left anterior negativity (LAN), and this was negatively correlated with a subsequent P600, suggesting that LAN and P600 within the same anomaly type also trade off. N400 effects were less variable in time than P600 effects, leading to consistently larger effect sizes for N400 than P600 effects. Overall, the results suggest important considerations for language processing ERP studies, including: 1) N400 effects will sometimes appear instead of, and obscure P600 effects, due to inter-individual differences in the population; 2) the LAN may be an artifact of component overlap between N400 and P600 activity within a group of participants.
Topic Area: LANGUAGE: Syntax