Local features bootstrap gist perception of scenes

Natural scenes have a complex structure in terms of the variety of objects they contain and the spatial arrangements of these objects. Yet, visual perception of scenes appears to be automatic and rapid (Biederman, 1972; Potter, 1975, 1976). We used a rapid priming paradigm to investigate if local structures are used during the first milliseconds to bootstrap scene processing for obtaining the gist of a briefly presented natural scene. Local structure we defined as visual information that survives image scrambling with intact units of 1.4 degree in size. ‘Gist’ is the information, which allows an observer to perform scene categorisation defined by choosing a target from the test scene as a response prompt, and not a distractor from a very different scene. In our experiments, a scrambled version of the test scene (42 ms) was presented before the onset of the intact scene (28ms), followed by a mask. Results: The scrambled frame significantly facilitates the perception of the gist of a scene but the facilitation is incomplete (Exp. 1). This facilitation is not due to luminance and colour distributions (Exp. 2), and significant facilitation occurs only when the scrambled frame is presented immediately before or after the intact frame (Exp. 3). Lastly, local structure of one scene can facilitate the perception of a similar scene, but the effect is significantly reduced. Taken together, our results suggest that local structures have a significant contribution to rapid scene perception, and rapid scene perception relies on the integration of diverse sources of information that are available within a brief time frame