Wheatstone and the origins of moving stereoscopic images.

The recent resurgence of stereoscopic films and television programmes occasions reflection on their origins. Experimental studies of stroboscopic (apparent) motion and stereoscopic vision have their origins in London in the decade from 1825 to 1835. Instruments were devised which simulated motion and depth: sequences of still images could appear to move, and paired pictures (with small horizontal disparities and presented to different eyes) were seen in depth. Until that time, the experience of motion was almost always a consequence of object or observer movement: apparent motion was a novelty. By contrast, stereoscopic vision was the near-universal experience of using two eyes in the natural environment, but its basis remained mysterious. The stereoscope rendered the normal conditions for seeing depth from disparity experimentally tractable. The instruments were called philosophical toys because they fulfilled the dual roles of furthering scientific experiment on the senses and of providing popular amusement. The investigations were initially driven by the need for stimulus control so that the methods of physics could be applied to the study of perceptual phenomena. Many varieties of stroboscopic discs and stereoscopes were devised thereafter and their popularity increased enormously after 1840, when combined with photography. Presenting sequences of stereoscopic photographs in apparent motion was attempted in the 1850s, but proved less successful. The catalyst involved in all these developments was Charles Wheatstone.