How long to get to the "gist" of real-world natural scenes?

This study aimed at assessing the processing time of a natural scene in a fast categorization task of its context or "gist". In Experiment 1, human subjects performed 4 go/no-go categorization tasks in succession with colour pictures of' real-world scenes belonging to 2 natural categories: "Sea" and "mountain" and 2 artificial categories: "Indoor" and "urban". Experiment 2 used colour and grey-level scenes in the same tasks to assess the role of colour cues on performance. Pictures were flashed for 26 ms. Both experiments showed that the gist of' realworld scenes can be extracted with high accuracy (90%), short median RT (400-460 ms) and early responses triggered latencies as short as 200-300 ms. Natural scenes were processed faster than artificial scenes. Categories for which colour could have a diagnostic value were processed faster in colour than in grey. Finally, processing speed is compared for scene and object categorization tasks.