Watanabe Illusion (2010)

<b>Watanabe Illusion (2010)</b><b>渡辺錯視（2010）</b>The “Watanabe illusion” (Watanabe, 2010) is a visual illusion in which observers underestimate the slope of a short line segment; in other words, it is a phenomenon in which the perceived orientation of the line segment is pulled toward the horizontal. The stimulus for this illusion consists of a circle containing a diagonal line in the lower-left corner and a horizontal rectangle with dots arranged at regular intervals along its right edge.Although the line is designed so that its extension intersects with the topmost dot, observers consistently estimate the intersection point to be several dots lower, demonstrating a systematic underestimation of the slope.There are several variations of the “Watanabe illusion.” One is an illustration featuring a circle placed in the lower left corner with a line segment drawn inside it. The perceived direction of the line segment’s extension is shifted toward the horizontal line.Another is an illusion featuring two eyes. The position of the pupils is perceived as shifted toward the horizontal line. Yet another is an illustration of a girl drawing a bow. The extension of the arrow is perceived as shifted toward the horizontal line.The circle and line segment illusion is caused by a bias toward a simple horizontal or vertical line, while the bow and arrow illusion is caused by a bias toward a horizontal or vertical line in 3D space.<br>