Camouflage and visual perception

Abstract

How does an animal conceal itself from visual detection by other animals? This review paper seeks to identify general principles that may apply in this broad area. It considers mechanisms of visual encoding, of grouping and object encoding, and of search. In most cases, the evidence base comes from studies of humans or species whose vision approximates to that of humans. The effort is hampered by a relatively sparse literature on visual function in natural environments and with complex foraging tasks. However, some general constraints emerge as being potentially powerful principles in understanding concealment-a 'constraint' here means a set of simplifying assumptions. Strategies that disrupt the unambiguous encoding of discontinuities of intensity (edges), and of other key visual attributes, such as motion, are key here. Similar strategies may also defeat grouping and object-encoding mechanisms. Finally, the paper considers how we may understand the processes of search for complex targets in complex scenes. The aim is to provide a number of pointers towards issues, which may be of assistance in understanding camouflage and concealment, particularly with reference to how visual systems can detect the shape of complex, concealed objects.

Cuttlefish use visual cues to determine arm postures for camouflage

“…perhaps via edge detection) or recognition by predators, particularly if postural and shape changes also enhance general background resemblance. Because a predator has to be familiar with a prey's specific three-dimensional shape to identify and detect it [47], an alteration in body shape (as in the case of an octopus) or arm posture (in cuttlefish and squids) might enhance camouflage by interfering with the predator's search image. Anecdotal evidence also suggests that cuttlefish and squid wave their arms and body, respectively, according to the movement of background elements [39,40] and by doing so render themselves less distinguishable [47].…”

Cuttlefish camouflage: context-dependent body pattern use during motion

“…Personal observations (S. Zylinski) suggest that such environmental motion often results in the movement of seaweeds, small substrate particles and biological matter, all of which tend to reflect light at low intensities. Conversely, edgy areas of high contrast tend to be associated with larger objects such as pebbles and shells (figure 4), which are less susceptible to being moved by the surrounding water (Troscianko et al 2009). The Gestalt laws of perceptual organization show that image regions are grouped by common fate; image components that move together tend to be grouped together (Bruce & Green 1990).…”

“…Given the difficulties of remaining undetected during movement, an alternative strategy is to concentrate efforts on avoiding capture once detected. High-contrast dazzle markings, or 'motion dazzle', are proposed to foil capture by interfering with motion detection mechanisms, and hence misleading the viewer as to the direction and/or speed of movement (Stevens et al 2008;Troscianko et al 2009). Despite their counterintuitive appearance, dazzle markings have a longstanding military application, used by the British and American navies in World War I to disguise the speed and direction of ships (Behrens 1999).…”

Motion dazzle: a locust's eye view

“…Therefore, there was an antagonistic effect on the DCMD response when the patterning of a looming stimulus caused its expanding edges to elicit both ON and OFF stimulation to different areas of the eye (see also [9]). The antagonistic effect of integrating these potentially conflicting local sensations resembles current explanations for motion dazzle in humans [2,17].…”