Centre-surround effects on perceived orientation in complex images.

Using the simultaneous tilt illusion [Gibson, J., & Radner, M. (1937). Adaptation, after-effect and contrast in the perception of tilted lines. Journal of Experimental Psychology, 12, 453-467], we investigate the perception of orientation in natural images and textures with similar statistical properties. We show that the illusion increases if observers judge the average orientation of textures rather than sinusoidal gratings. Furthermore, the illusion can be induced by surrounding textures with a broad range of orientations, even those without a clearly perceivable orientation. A robust illusion is induced by natural images, and is increased by randomising the phase spectra of those images. We present a simple model of orientation processing that can accommodate most of our observations.