With monocular viewing, forty observers judged a monochrome-gray and a polychrome hollow face mask (illuminated from above, from below, from the right and from the left, and upside-down illuminated form below) as inward deep, flat or outward deep. They were also asked to reproduce the perceived depth of the mask by pulling out a tape measure. Regardless of color, illuminating condition and mask orientation, most of the responses indicated that the hollow faces were perceived as outward deep. Even in the few occasions in which the masks were reported flat, measurable depths were assigned on the tape measure. These results support that the hollow face illusion is robust even under diverse variable effects, which suggest preponderant top-down over bottom-up processes on visual face perception.
hollow-face illusion; visually perceived depth inversion; face perception
