Double Vision as a Pictorial Depth Cue

Abstract

"Double images" are a little-noticed feature of human binocular vision caused by nonconvergence of the eyes outside of the point of fixation. Double vision, or psychological diplopia, is closely linked to the perception of depth in natural vision as its" perceived properties vary depending on proximity of the stimulus to the viewer. Very little attention, however, has been paid to double images in art or in scientific studies of pictorial depth. Double images have rarely been depicted and do not appear among the list of commonly cited monocular depth cues. In this study we discuss some attempts by artists to capture the doubled appearance of objects in pictures, and some of the relevant scientific work on double vision. We then present the results of a study designed to test whether the inclusion of double images in twodimensional pictures can enhance the illusion of three-dimensional space. Our results suggest that double images can significantly enhance depth perception in pictures when combined with other depth cues such as blur. We conclude that double images could be added to the list of depth cues available to those wanting to create a greater sense of depth in pictures.1 Email address for correspondence: rpepperell@cardiffmet.ac.uk Double vision and artArtists have various techniques at their disposal for conveying a sense of depth in pictures. These include occlusion, shading and shadows, relative size within the picture plane, and various kinds of perspective. Through skillful use of these techniques the artist can create a highly convincing illusion of three-dimensional space on a two-dimensional surface (Pirenne, 1970). These so called ‗pictorial depth cues' have also been of long-standing interest to scientists studying visual perception, and there is a well-established list of such cues to be found in standard texts on vision (Palmer, 1999).Pictorial depth cues, however, suffer from the limitation that they are monocular, that is, they present image of the world as it appears to one eye only. Very few attempts In a painting such as ‗Self Portrait with Candles' (Fig. 1) We owe a great debt to Walters' former partner Erna Meinel for promoting a wider understanding of his work. After Walters' death Meinel published a paper describing his methods (Meinel, 1973) and wrote a well-informed book summarizing its' theoretical underpinning, which sadly was also never published (Meinel, undated).Meinel's writings offer both a first hand account of the artists' thinking process and corroboration of his findings in contemporary vision science research. In this she benefitted from intimate acquaintance with Walters himself and her own scientific training.In Meinel's and Walters' view the inclusion of double images in pictures can significantly enhance the illusion of depth (Walters, 1940). Like others, they recognised that a flat picture can never fully replicate fully three-dimensional space (Wade and Ono, 2012). In natural vision double images are seen separately by each eye and outside the ‗focal pla...

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“…Likewise, the phenomenon of physiological diplopia, or “double vision”, has long been recognized as a fundamental feature of natural vision and critical to the perception of depth [67]. Despite this, its potential to function as one of the so-called “monocular depth cues”, which we use to infer depth from pictures, by simulating it in 2D images has barely been exploited because it is widely assumed double vision is “screened out” of conscious vision [68,69].…”

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