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Wendy Adams, Matt Anderson, Erich Graf; Binocular depth cues break camouflage. Journal of Vision 2018;18(10):722. doi: 10.1167/18.10.722.
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Many species employ camouflage to disguise their true shape. One type of disruptive colouration, 'edge enhancement', can be used to create salient, illusory depth edges within an animal's body, whilst their true outline blends into the background. Binocular vision could provide a critical advantage in the arms race between perception and camouflage: binocular disparities reveal the true depth structure of the scene. However, little is known about whether stereopsis can 'break' camouflage. Human observers were asked to locate snake targets embedded in leafy backgrounds. We analysed performance (response time) as a function of edge enhancement, illumination, and the availability of binocular depth cues. We confirmed that edge enhancement contributes to effective camouflage: observers were slower to find snakes whose patterning contained 'fake' depth edges. Importantly, however, this effect disappeared when binocular depth cues were available. Illumination also affected snake detection: when scenes were rendered under directional illumination, such that both the leaves and snake produced strong cast shadows, snake targets were localised more quickly than in scenes rendered under ambient illumination. This facilitatory effect was reduced, but still significant under stereoscopic viewing. In summary, our data suggest that both binocular disparity and directional illumination improve detection by providing information about the true 3D structure of a scene. Moreover, the strong interaction between disparity and edge enhancement suggests that binocular vision has a critical role in breaking camouflage – to ensure that misleading pictorial depth cues, which suggest the presence of depth discontinuities, are overruled.
Meeting abstract presented at VSS 2018
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