Attention-free integration of spatial frequency-based information in natural scenes.

The integration of visual image information provided by low and high spatial frequency channels is critical to rapid perception of natural scenes. However, little is known about the role of attention in integrating this information. In two experiments, using attention-demanding tasks, we examined the advantage of integration, i.e. the superior categorization accuracies for images, using a wide range of different spatial frequencies. In Experiment 1, a spatially central to-be-identified letter and a peripheral filtered image of a natural scene appeared simultaneously. In Experiment 2, the letter and the image were presented sequentially at the same spatial location. In both experiments results consistently showed an advantage of integration in categorization behavior that was not influenced by attention-demanding tasks. This finding suggests that the integration of frequency-based information in natural scenes is attention-free.