%0 Journal Article
%T An Upward
%A Kazunori Morikawa
%A Yuki Kobayashi
%J Perception
%@ 1468-4233
%D 2019
%R 10.1177/0301006619847590
%X The human visual system can extract information on surface reflectance (lightness) from light intensity; this, however, confounds information on reflectance and illumination. We hypothesized that the visual system, to solve this lightness problem, utilizes the internally held prior assumption that illumination falls from above. Experiment 1 showed that an upward-facing surface is perceived to be darker than a downward-facing surface, proving our hypothesis. Experiment 2 showed the same results in the absence of explicit illumination cues. The effect of the light-from-left prior assumption was not observed in Experiment 3. The upward- and downward-facing surface stimuli in Experiments 1 and 2 showed no difference in a two-dimensional configuration or three-dimensional structure, and the participants¡¯ perceived lightness appeared to be affected by the observers¡¯ prior assumption that illumination is always from above. Other studies have not accounted for this illusory effect, and this study¡¯s finding provides additional insights into the study of lightness perception
%K lightness/brightness
%K light-from-above assumption
%K top-down processing
%K surface orientation
%K illumination
%U https://journals.sagepub.com/doi/full/10.1177/0301006619847590