Disruptive coloration and binocular disparity: breaking camouflage

Abstract

Many species employ camouflage to disguise their true shape and avoid detection or recognition. Disruptive coloration is a form of camouflage in which high-contrast patterns obscure internal features or break up an animal's outline. In particular, edge enhancement creates illusory, or ‘fake’ depth edges within the animal's body. Disruptive coloration often co-occurs with background matching, and together, these strategies make it difficult for an observer to visually segment an animal from its background. However, stereoscopic vision could provide a critical advantage in the arms race between perception and camouflage: the depth information provided by binocular disparities reveals the true three-dimensional layout of a scene, and might, therefore, help an observer to overcome the effects of disruptive coloration. Human observers located snake targets embedded in leafy backgrounds. We analysed performance (response time) as a function of edge enhancement, illumination conditions and the availability of binocular depth cues. We confirm that edge enhancement contributes to effective camouflage: observers were slower to find snakes whose patterning contains ‘fake’ depth edges. Importantly, however, this effect disappeared when binocular depth cues were available. Illumination also affected detection: under directional illumination, where both the leaves and snake produced strong cast shadows, snake targets were localized more quickly than in scenes rendered under ambient illumination. In summary, we show that illusory depth edges, created via disruptive coloration, help to conceal targets from human observers. However, cast shadows and binocular depth information improve detection by providing information about the true three-dimensional structure of a scene. Importantly, the strong interaction between disparity and edge enhancement suggests that stereoscopic vision has a critical role in breaking camouflage, enabling the observer to overcome the disruptive effects of edge enhancement.

Scaffolding depth cues and perceptual learning in VR to train stereovision: a proof of concept pilot study

“…Stereopsis plays a key role in extracting depth information from natural scenes 5 , breaking camouflage 6 , and planning and executing everyday visuomotor tasks 1 – 3 . However, abnormal visual experience during the “sensitive period” of development 7 , 8 may result in amblyopia and, as a result, in reduced or absent stereopsis 9 .…”

Finding a signal hidden among noise: how can predators overcome camouflage strategies?

“…This is likely owing to edge enhancement causing artificial depth, which is revealed when binocular disparity identifies the true three-dimensional shape of the object. Motion parallax-the differential shift in the relative positions of prey and substrates during predator movement-may also provide these cues but this does require predator movement to generate the shift [68]. Other higher level cognitive processes may also play a role in perceiving prey movement when camouflaged.…”

“…This means that prey have an additional characteristic they must hide in order to prevent detection. Binocular/static disparity has been shown to reduce the effectiveness of disruptive markings with edge enhancement, by clarifying the true three-dimensional structure of the camouflaged object [68], although it is less effective when faced with moving objects [69]. This is likely owing to edge enhancement causing artificial depth, which is revealed when binocular disparity identifies the true three-dimensional shape of the object.…”

Camouflage in a dynamic world

“…Differences in optic flow, because of differences in the correlation of apparent motion of objects in different depth planes, can be used to break camouflage, with or without stereopsis [19,20].…”