THE PRESENT PAPER REPORTS some preliminary experiments on the Ditchburn-Riggs effect which is obtained with stabilized images. Our results are such as to show that the original discovery, made independently by Ditchburn and Riggs and their collaborators about 1952, has opened a new and valuable avenue of approach to the analysis of visual perception.In normal visual fixation, die image that falls on the retina is never really stable; "physiological nystagmus," the continuous tremor of the normal eye at rest, causes a slight but constant variation in the rods and cones that are excited. It is now known that the variation plays a vital role in perception, for it was shown by Ditchburn and Cinsborg (1952) and Riggs, Ratliff, Cornsweet and Comsweet (1953) that stabilizing the image (experimentally eliminating variability of retinal excitation) leads rapidly to the disappearance of the visual object, followed by intermittent reappearanceIn their experiments, the target was projected on a screen after being reflected from a small mirror attached to a contact lens worn by the observer. Thus each slight involuntary movement of the "fixated" eye would produce a movement of the target. By having the subject observe through a complex optical system, it was possible to make the two movements correspond exactly: the angular extent and direction of the eye movement were matched by the movement of the target, cancelling out the normal tremor of the eye and producing a stabilized retinal image. In these conditions the line of demarcation between the two halves of a 1 degree field, separately lighted so as to give intensity ratios of up to 3:1, disappears intermittently for 2 to 3 sec., at intervals of about 1 min. (Ditchburn & Ginsborg, 1952). Similarly, within a few seconds of stabilized viewing, a thin black line crossing a bright 1 degree field fades out; coarser lines are seen for longer periods, but still intermittently, the length of time the line remains visible being a direct function of its thickness (Riggs et al., 1953).

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