It is said that visual fatigue caused by watching stereoscopic images
is due to the conflict between convergence eye movement and accommodation functions. We studied the degree of visual fatigue in subjects watching HDTV stereoscopic images. The HDTV stereoscopic images used as visual stimuli contained only absolute, with no relative, parallax. In the experiments, images were displayed behind or in front of the screen by a 120-Hz time-sequential method. The examination of visual fatigue was carried out with a five-grade subjective evaluation test and measurement of the accommodation response after watching for one hour. We found that when stereoscopic HDTV images were displayed within the corresponding range of depth of focus, and remained static in the depth direction, the degree of visual fatigue was almost the same as that induced by watching images displayed at the depth of the screen. However, when images were displayed outside the corresponding range of depth of focus, visual fatigue was clearly induced. Moreover, we found that even if images were displayed within the corresponding range of depth of focus, visual fatigue was induced if the images were moved in depth according
to a step pulse function.