The vertical parallax of both eyes, caused by tilting the head when watching three-dimensional (3D) television or movies, can induce visual fatigue or visually-induced motion sickness. The purpose of the present study was to investigate levels of discomfort and fatigue and eye movements induced by viewing a 3D movie with vertical parallax. Two experiments were conducted to investigate the relationship between the degree of vertical parallax and the magnitude of the effect. The results indicate that the viewer's feeling of visual malaise increases as the angle of the screen increases, with respect to the observer's head, because eye movement does not compensate for the parallax in the vertical direction. Binocular rivalry is believed to occur when viewing a 3D movie with vertical parallax, which may induce even more visual malaise.
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