Abstract
In natural scenes, shading and specular highlight often coexist under the same lighting condition. Previous studies have suggested independent mechanisms for these cues in the perception of 3D structure. Circular patterns with the same polarity of gradation pop out from those with the opposite polarity in an array of the patterns (Ramachandran, 1988). When the gradation is replaced by specular highlight (without shading) , the pop-out vanishes, suggesting fundamentally distinct mechanisms for shading and highlight. We investigated psychophysically the integration of specular highlight and shading in the perception of 3D structure. Specifically, we examined whether and how specular highlight facilitates the perception of 3D structure from shading, and analyzed the mechanism for the integration of the two cues. We performed psychophysical experiments in a visual search paradigm using the circular arrays with the expectation of pop-out based on shading. To control shading and highlight, we integrated a variety of real/realistic specular highlights into artificial shading. A single circular pattern including a gradation (target) was embedded into an array of circular patterns including the opposite polarity of gradation (distractors). The participants were asked to answer when one found the target. The results showed that combinations of highlight and shading reduce significantly the reaction time. This reduction holds even when specular highlight is inconsistent with shading, indicating that highlight and shading work in a facilitative fashion but not in suppressive. Furthermore, the analysis of the reaction time indicated that specular highlight facilitates multiplicatively the perception of 3D structure, and that the facilitation depends on the characteristics of specular highlight including the direction of light source. These results support that the cortical mechanisms for shading and specular highlights in 3D perception are independent, and that they are integrated in a highly nonlinear fashion.
Meeting abstract presented at VSS 2012