FROM BLOBS TO BOUNDARY EDGES - EVIDENCE FOR TIME-SCALE-DEPENDENT AND SPATIAL-SCALE-DEPENDENT SCENE RECOGNITION

In very fast recognition tasks, scenes are identified as fast as isola ted objects. How can this efficiency be achieved, considering the larg e number of component objects and interfering factors, such as cast sh adows and occlusions? Scene categories tend to have distinct and typic al spatial organizations of their major components. If human perceptua l structures were tuned to extract this information early in processin g, a coarse-to-fine process could account for efficient scene recognit ion: A coarse description of the input scene (oriented ''blobs'' in a particular spatial organization) would initiate recognition before the identity of the objects is processed. We report two experiments that contrast the respective roles of coarse and fine information in fast i dentification of natural scenes. The first experiment investigated whe ther coarse and fine information were used at different stages of proc essing. The second experiment tested whether coarse-to-fine processing accounts for fast scene categorization. The data suggest that recogni tion occurs at both coarse and fine spatial scales. By attending first to the coarse scale, the visual system can get a quick and rough esti mate of the input to activate scene schemas in memory; attending to fi ne information allows refinement, or refutation, of the raw estimate.