2004 年 23 巻 1 号 p. 111-112
Recent studies suggest that the shape of three-dimensional (3-D) objects causes the systematic distortion of their apparent size (Miura & Taya, 2001) and we have investigated which property of the objects may do this. The stimuli were stereograms defining four 3-D shapes: a pair of frontoparallel rectangles, a triangular ridge, a cylindrical ridge, and a trapezoidal ridge. The observer's task was to match the height of a line-drawing of a rectangle (comparison stimulus) to that of the stimuli. The results showed that the apparent height of the object decreased as the slant of their surface protruding from the background was increased. The results implied that our visual system takes account of the slant of a surface for size estimation.