Fragmentation of a Geometrical Figure viewed under Intermittent Illumination

Abstract

WHEN a simple target is viewed as a currently occurring retinal image which is confined to a specific locus, the target has been reported to lose contrast and to disappear^1–3. The restriction of an image to a specific retinal locus is commonly termed a “stabilized retinal image”. This is the reverse situation to that encountered in normal vision where eye movements change the position of the retinal image several times a second. For more complex targets such as geometrical figures viewed as stabilized retinal images, intermittent disappearance and reappearance of the figure in whole or in part have been reported^4–7. This striking phenomenon, usually outside the subject's previous visual experience, has been termed “fragmentation”. The common methods of investigating fragmentation are voluntary steady fixation, viewing as a partially stabilized retinal image using a contact lens and as a prolonged after-image (a completely stabilized retinal event)^4–7. These methods in order progressively impose restraint on the image with respect to its retinal locus. Another method of investigating fragmentation was described by Evans⁸ and McFarland⁹. who note reports of fragmentation by subjects viewing geometrical figures for brief time intervals. Typically, the stimulus is viewed tachistoscopically near the recognition threshold after which the subject records his observations. This sequence is then repeated for many trials. We wish to describe another method of producing and studying fragmentation, by viewing a geometrical figure under intermittent illumination.