Brightness reversal in the natural visual environment: a Venetian blind effect.
If a partially open Venetian blind is lighted by the sun, or by diffuse light from the sky, then the upper portion of each slat will be brightly lighted and the lower portion shaded. If an observer moves the head downward while viewing a dark object silhouetted against the sky, then the object displays a reversal of brightness, appearing brighter than the sky while the head is moving downward. Moving the head upward produces no brightness reversal. These observations in the natural visual environment are consistent with earlier laboratory demonstration under several conditions.
D000360:Afterimage / Q000502:physiology*; D005403:Fixation, Ocular; D006801:Humans; D007088:Illusions / Q000502:physiology*; D009068:Movement; D009903:Optical Illusions / Q000502:physiology*