Abstract. The present study investigated the temporal dynamics of the object-scene congruity during a categorization task of objects embedded in a scene. Participants (n = 28) categorized objects in scenes as natural or man-made while event-related brain potentials (ERPs) were recorded. The object-scene associations were either congruous (e.g., a tent in a field) or incongruous (e.g., a fridge in a desert). The results confirmed that contextual congruity affects item processing in the 300–500 ms time window with larger N300/N400 complex in the incongruous than in the congruous condition. However, unlike previous work which found an effect of congruity starting at ~ 250 ms poststimulus on fronto-central regions, the earliest sign of a reliable context congruity effect arose at ~ 170 ms at left centro-parietal regions in the present study. The present results are in line with those of previous studies showing that object and context are processed in parallel with continuous interactions from 150 to 500 ms, possibly through feed-forward co-activation of populations of neurons selective to the processing of the object and its context. The present finding provides novel evidence suggesting that online context violations might affect earlier visual processes and routines of matching between possible scene-congruent activated schemas and the upcoming information about the item to process.

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In this event-related potential (ERP) study, we investigated the effects of format change and semantic relatedness in a recognition task using pairs composed of a word and a line drawing. The semantic relatedness of the pairs (related: rabbit-carrot; unrelated: duck-artichoke) influenced their associative properties and corresponding distinctiveness, while format change refers to the switching of an item from the verbal form to the line drawing form between study and recognition (e.g., the word "egg" is associated with a drawing of a hen at study, and a line drawing of an egg is associated with the word "hen" at test). Study-test format change thus prevents visual matching while maintaining conceptual matching. While the N300 potential was only modulated by the semantic relatedness of the pair, both factors modulated recognition performance and corresponding ERP old/new effects with larger mid-frontal N400 old/new effect (300-500 ms) and larger parietal old/new effect (500-800 ms) in the same compared to the different-format condition, as well as for related compared to unrelated pairs. Furthermore, the semantic relatedness of correctly recognized old pairs modulated the anterior N400 while it modulated the posterior N400 for correctly rejected pairs. These results suggest that semantic relatedness and familiarity related to the amount of change between study and test present distinct ERP signatures in the N400 window. They suggest also that the distinctiveness and the ease of the retrieval of the pair could be determining for the parietal old/new effect.