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H A Sedgwick, Grace Tran; Spatial compression produced by a stationary telescope. Journal of Vision 2006;6(6):737. doi: 10.1167/6.6.737.
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A telescope compresses optically specified distance. Shah and Sedgwick (2004), measuring perceived distance using a walking task with free head movements, found much less telescopic compression of perceived distance than was optically specified. They also found no significant difference in perceptual compression between a telescope and a plain tube having the same field of view. Our study measured the compression in depth of perceived shape while looking through a stationary telescope. A 2.75× telescope was mounted 40 cm above a tabletop patterned with receding stripes. The 11.6 degree field of view was centered on a series of rectangular stimulus cards lying flat on the table at a distance of 100 cm. Participants monocularly viewed each card through the telescope, or through a tube having the same field of view, and verbally judged the card's perceived length (in depth) relative to its width (in the frontal plane). Perceptual compression of shape was calculated by dividing the perceived proportion (length/width) by the actual proportion. The telescope and the tube both produced significant perceptual compression, but perception was significantly more compressed through the telescope (0.43) than through the tube (0.52). The perceptual compression produced by our stationary telescope matched the optically specified compression (0.43) that we calculated based on the telescope's magnification and viewing angle. In addition, monocular vision, restricted head movements, and a restricted field of view may have contributed to the compression in depth of perceived shape with both the tube and the telescope.
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