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Short-Term Memory in Vision

01 January 1961

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There can be little doubt that eye movements play an important role in the perception of form, and that perceptions of complicated visual fields are built up from information gathered during many fixations of the eyes. But eye movements over a complicated visual field are unpredictable from subject to subject and from time to time with the same subject. They may therefore be an annoying source of variability in perceptual experiments, and experimenters frequently find it desirable to eliminate them. This is usually done by using a tachistoscope, a device for presenting brief exposures of visual material. The position of the eyes is kept fixed at the crucial time by having the subject fix his eyes before exposure of the material, and by using exposures sufficiently brief that, the subject cannot change his fixation during the exposure. To accomplish this, exposure times must be less than the reaction time of the eye for a change of fixation (150-200 milliseconds). Actual measurement in a tachistoscopic situation has shown that exposures of 100 milliseconds or shorter satisfy this purpose. 1 At first thought, it may seem unreasonable to study visual perception under the peculiar condition of tachistoscopic experiments. Some question might be raised about whether data obtained in this way can be generalized to natural perceptual situations. It can be argued, however, that in a very real sense the tachistoscopic situation is not an unnatural one. For it is well established that, in scanning pictorial or printed mate309