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The P600 as a Graded Index of Integration Difficulty

Poster B2 in Poster Session B and Reception, Thursday, October 6, 6:30 - 8:30 pm EDT, Millennium Hall

Christoph Aurnhammer¹, Francesca Delogu¹, Harm Brouwer¹, Matthew W. Crocker¹; ¹Saarland University

While the N400 and P600 are the most salient ERP indices of language processing, it remains under debate which component indexes integration processes (e.g., Brouwer et al., 2017, Rabovsky et al., 2018). A recent study (Aurnhammer et al., 2021) demonstrated their differential sensitivity to how associated a word is to the context (N400 alone) versus how contextually expected it is (N400 and P600). Further, a post-hoc analysis suggested that rather than being a binary index of expectancy violations, the P600 - like the N400 - may actually be sensitive to expectancy in a graded manner. These results are consistent with the view that the N400 indexes retrieval, and the P600 indexes integration. The current experiment directly examines whether the P600 provides a graded index of integration difficulty. As late positivities are difficult to interpret due to spatio-temporal overlap with the N400 component, we sought to minimise N400 differences across conditions by adapting an experimental design (“the lady told the tourist / suitcase”, Nieuwland & Van Berkum, 2005), in which both plausible and implausible target words are presented several times in a preceding context paragraph. The absence of an N400-effect for such designs has been attributed to the substantial priming of the targets by their previous repetition (Brouwer et al., 2012), with the original study revealing only a broad positivity for the implausible vs. plausible targets. The current study further includes a condition with intermediate plausibility (B) – as measured in a pre-test – and employs a context, rather than target, manipulation (“the lady dismissed (A) / weighed (B) / signed (C) the tourist”). Importantly, this intermediate condition raises expectations for a more plausible alternative, creating a prediction disconfirmation. This allows us to assess whether such disconfirmations have additional influence on late positivities for somewhat plausible target words beyond what is explained by plausibility alone – and in absence of component overlap with the N400. An initial self-paced reading experiment revealed that reading times on spillover regions are graded for plausibility, but not affected by disconfirmations. In the EEG data, we obtained an earlier negativity for Condition B, which we take to be driven by the prediction disconfirmation, while no N400 difference was observed for either condition B or C relative to baseline. Late positivities were graded for plausibility. An rERP analysis revealed that, while the majority of the parietally distributed late positivities is explained by plausibility, condition B elicited an additional left-frontocentral positivity in response to the presence of an expected alternative, in line with prior research. The absence of any N400-effects of plausibility replicates the previous finding for target words present in the context, consistent with retrieval being facilitated by repetition. In contrast, we do observe graded P600 modulations across three levels of plausibility, consistent with the P600 as integration hypothesis, and contrasting with the P600 as reflecting error detection/correction. These findings reveal a critical novel dimension to the functional interpretation of the P600 with important implications for existing and future neurocognitive experiments and theories.

Topic Areas: Meaning: Discourse and Pragmatics, Meaning: Combinatorial Semantics