Nieuwland, M. S. & Martin, A. E.
Basque Center on Cognition, Brain and Language
Counterfactual comprehension provides an interesting test-case for studying the interaction between real-world knowledge and discourse context because counterfactuals may require keeping in mind both what is true and what happens to be false. Recent event-related potential (ERP) and eye-tracking results suggest that real-world knowledge briefly interferes with counterfactual comprehension, consistent with two-stage accounts of discourse comprehension. In an ERP experiment, we tested whether real-world interference upholds when incoming information is highly predictable from the counterfactual context. Participants read 120 counterfactually true/false statements (“If N.A.S.A. had not developed its Apollo Project, the first country to land on the moon would be Russia/America”) and real-world true/false statements (“Because N.A.S.A. developed its Apollo Project, the first country to land on the moon has been America/Russia"). Based on results from independent pre-tests, counterfactual and real-world statements were matched for critical word expectancy and average truth-value rating. Our hypothesis involved N400 ERP amplitude, which indexes early semantic processing and is sensitive to subtle variations in discourse-semantic fit. If real-world knowledge interferes with counterfactual comprehension despite this strong context, then critical words in counterfactually true statements should evoke larger N400s than counterfactual false statements and real-world true statements. In contrast, if incoming words are mapped onto the most relevant interpretive context without delay and without initial regard to real-world truth-value, then false statements should elicit an N400 effect compared to true statements, for counterfactual and real-world statements alike. Our results support this latter hypothesis: counterfactually false sentences elicited an N400 effect compared to counterfactually true sentences, identical to the N400 effect for real-world sentences. These results argue against interference from real-world knowledge during counterfactual comprehension. Instead, they suggest that incoming words are mapped onto discourse context without any delay if they are sufficiently plausible and predictable given this context, whether factual or counterfactual.