Are incongruent objects harder to identify? The functional significance of the N300 component

摘要

Objects in the real world typically appear within a broader context, having relationships with the environment. Do these relations between objects and the contexts in which they appear affect object identification? Previous findings of an N300 component evoked by scene-incongruent objects were taken as evidence for such an effect, since N300 is held to reflect object identification processes. Yet this conjuncture was never directly tested, and ignores differences between the fronto-central incongruency-evoked N300 and the typically bi-polar fronto-occipital identification-related N300. Here, the possible influence of context on object identification was examined by manipulating both object-scene congruency and object identifiability. N300 effects were found both for incongruity and for identifiability, in line with previous studies. Critically, a comparison of divergence times of waveforms evoked by congruent/incongruent objects and waveforms evoked by unidentifiable objects showed that incongruent objects started to diverge from unidentifiable ones later than congruent objects did. This provides first direct evidence for the effect of scene context on object identification; arguably, rapidly extracted gist activates scene-congruent schemas which facilitate the identification of congruent objects in comparison to incongruent ones.