Abstract
Stereograms are pairs of images that differ in the relative lateral displacement of elements such that, when viewed stereoscopically, they produce compelling illusions of depth from a completely flat surface. In the meantime, prolonged steady viewing of an achromatic stimulus with high contrast produces afterimage that has opposite lightness of its original stimulus. This study examined if a stereogram that consists of a veridical image for one eye and a lightness afterimage for the other eye produces depth perception. In experiment, human subjects observed computer-generated stimuli with a mirror stereoscope in a darkroom. Each trial of the experiment consisted of an adaptation phase and a test phase. Random-dot stereograms, in which a central square area had crossed or uncrossed disparity against the surround area, were used. In an adaptation phase, a random-dot image that consisted of white colored dots on black background was displayed to one eye, while the other eye's image was fully black. Subject stared at a fixation point provided at the center of the stimulus for 45 seconds. In a test phase, the random-dot image was erased and fully white display was alternatively given to the one eye, while the half of the random-dot stereogram was given as a veridical image, black dots on white background, to the other eye. Ten subjects, every subject could perceive depth from conventional random-dot stereograms and lightness afterimage took part in the experiment. As the experimental result, all the subjects perceived depth from the stereograms with lightness afterimages and veridical images.