Diagnostic Colors Contribute to the Early Stages of Scene Categorization: Behavioral and Neurophysiological Evidence

Abstract

We examined the effects of color cues on the express categorization of natural scenes. Using a go/no-go paradigm known to be sensitive to fast recognition processes, we measured the early Event Related Potential (ERP) correlates of scene categorization behavior to elucidate the processing stage at which colors contribute. Observers were presented with scene pictures belonging to four color-diagnostic categories (desert, forest, canyon and coastline). Scene pictures could come in one of three forms: diagnostically colored, gray-scale and nondiagnostically colored. In a verification task, observers were instructed to respond whenever the presented scene picture matched with a previously presented category name. Reaction times and categorization accuracy were optimal when the stimuli were presented in their original diagnostically colored version, followed by their gray-scale version, followed by their nondiagostically colored version. These effects were mirrored in the early (i.e. 150 ms following stimulus onset) ERP frontal correlates, whose onset was sped up for diagnostically colored (in comparison to gray-scale), and also for diagnostically colored and gray-scale (in comparison to nondiagnostically colored scenes). Frontal ERP amplitudes were also decreased for gray-scale and nondiagnostically colored scenes. Together, the results suggest that diagnostic colors are part of the scene gist responsible for express scene categorizations.