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Maxime Cauchoix, Michèle Fabre-Thorpe, Denis Fize; Dealing with natural scenes: Electrocorticographic correlates of object and context processing in Rhesus Monkey. Journal of Vision 2009;9(8):960. doi: 10.1167/9.8.960.
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© ARVO (1962-2015); The Authors (2016-present)
In the real world, objects never appear isolated but embedded in a meaningful context. We recently showed, at behavioral level, that context can influence rapid object categorisation in both Human [Joubert & al. 2008] and Macaque [Fize, Cauchoix, Fabre-Thorpe, Submitted]. Whereas neural correlates of object recognition have been largely studied in monkey, we know very little about neural coding of scene's context, its interaction with object processing and its possible precedence.
Here we investigate context and object coding at the neural population level on two head-free monkeys engaged in a rapid go/no go visual categorisation task while their electrocorticogram were simultaneously recorded. Stimuli were manipulated photographs composed by objects embedded in natural environments or man-made contexts. The animal/non-animal categorisation task thus used both categorically congruent objects and contexts (animal and natural context, manmade object and context) and incongruent ones (animal in a manmade context, manmade object in a natural context).
From averaged evoked potentials, we first confirmed the existence in V4 of a differential activity between animals and manmade objects picking at 96ms [Fize & al, Submitted]. Moreover we found that scene's contexts, which were irrelevant for the task, induced a strong differential activity in a neighbouring electrode 20ms earlier. Finally, using single trial time-frequency analyses, we evidenced stronger low frequencies (3–5Hz) phase synchronisation when objects were presented in a congruent context than in an incongruent one, around 80ms after stimulus onset.
During the rapid visual processing of natural scenes, neural signatures of context and object processing and their interaction occur in the neighborhood of V4 area in less than 100ms after stimuli onset.
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