Abstract
Object and context processing interfere in rapid object visual categorization of briefly flashed natural scenes, suggesting that objects and context in a visual scene are processed in parallel with strong early interactions (Joubert et al. 2008). The present fMRI study aimed to investigate cerebral activations elicited by the processing of scenes with either congruent or incongruent object/context relationships. Fifteen subjects were instructed to categorize objects (man-made objects or animals) in briefly presented stimuli (exposure duration = 100 ms), using a forced-choice two-button response. Half the objects were pasted in expected (congruent) contexts, whereas the other half was shown in incongruent contexts. Our behavioural results support previously reported data, showing that object categorization is more accurate (+14%) and faster (-32ms) in congruent vs. incongruent scenes. Moreover, we found that both types of scenes elicited differential neural processing. The processing of non congruent scenes induced increased activations in the right parahippocampal and retrosplenial cortices, as well as in the right middle frontal gyrus (P <0.05 corrected). This higher activity may be due to additional processing of the novel (unfamiliar) relationships between object and context that were inherent to the incongruent scenes. In particular, the increase of activity in the anterior part of the right parahippocampal cortex, previously shown to be involved in object/context binding (Goh et al. 2004), was correlated (P <0.05) with the delay, i.e. increase of reaction time, necessary to process the objects in incongruent contexts. In this region, supplementary neural processing for incongruent scenes could therefore be related to impaired object categorization performance. Joubert et al. (2008) J Vis 8 (13): 11, 1-18 Goh et al. (2004) J Neurosci 24 : 10223-10228