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Poster D32, Wednesday, August 21, 2019, 5:15 – 7:00 pm, Restaurant Hall

Category-Level Semantic Top-Down Modulation of the N170

Jack E. Taylor1, Sara C. Sereno1, Guillaume Rousselet1;1University of Glasgow

INTRODUCTION: A common feature of current models of visual word recognition is the notion that readers' predictions of upcoming words, given semantic context, extend to the top-down prediction of visual word forms. One electroencephalography (EEG) component consistently shown to be sensitive to features of visual word forms is the N170. The present EEG study examined whether the N170 is sensitive to category-level semantic top-down modulation. METHODS: Participants (N=31) were presented with 496 stimuli, comprising equal numbers (N=124) of category-relevant words, control words, pseudowords, and random consonant strings. These were presented in two tasks: a lexical decision task (LDT) and a semantic categorisation task (SCT). Category-relevant words could belong to one of 6 categories of concrete nouns (presented in blocks). Control words were category-irrelevant and matched closely in terms of length and word frequency. Pseudowords and consonant strings were matched in terms of length. The order of tasks and laterality of button responses were both counterbalanced randomly. It was expected that if participants actively predicted visual word forms of words in the relevant category, there would be a task-stimulus interaction in the N170. Specifically, it would be expected that there would be reduced amplitude (and possibly earlier latency) in the N170 for category-relevant words in the SCT relative to the LDT. Control words, meanwhile, would show no task effect. RESULTS: Left-lateralised N170 amplitude and latency was analysed at the trial level with a linear mixed effects model. While the previous finding of bottom-up sensitivity to word-like visual word forms was replicated in differences in amplitude and latency between random consonant strings and control words, no evidence of an interaction between task and stimulus was found. To quantify the extent to which there was evidence for the null hypothesis, a Bayesian mixed effects model was fit with the same maximal structure as the linear mixed effects model. The hypothesis that the interaction between task and stimulus was equal to zero was favoured 100.74 times over the alternative hypothesis for N170 amplitude, and 105.18 times for N170 latency. CONCLUSION: It is suggested that if word form prediction in the N170 is indeed sensitive to semantic-level top-down modulation, then this is only detectable with a narrower range of candidate predictions than is possible at the level of semantic category.

Themes: Meaning: Lexical Semantics, Reading
Method: Electrophysiology (MEG/EEG/ECOG)

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