The Hollow Face Illusion Strength in Stereoscopic viewing Condition under Effects of Color, Ligthning Orientation and Rotation

The hollow-face illusion is an optical illusion in which the perception of a concave mask appears as a convex face. The goal of this study was to investigate the strength of this illusion under different sources of illumination, face color and positioning into stereographic photos. Forty participants judged, in a computer screen, the hollow-face illuminated from above, below, left, and right, and in the upside-down position illuminated from below, as concave, plain or convex. Most of them judged the reverse mask as convex. They also reproduced, in centimeters, the perceived depth of the mask using a retractable tape measure. No significant difference was observed between the colors, F(1,39)=. 22; p>.05. But there was an effect in the illumination directions, F(4,156)= 11.35; p<.05. The position affected the depth perception of a monochrome hollow-face, t(39)= 2.12; p<.05. Higher estimates were designated to the hollow-face in the upright position. These results indicated top-down overlapped bottom-up processing.