The computational neuroscience of animal camouflage

Lead Research Organisation: University of Bristol
Department Name: Biological Sciences

Abstract

From the moment 'The Origin of Species' was published in 1859, Darwin and his contemporaries used animal camouflage to illustrate how improved survival leads to apparent design. The ideas of early evolutionary biologists (and it is probably significant that many were artists too) in turn had a strong influence on the adoption of camouflage by the military in both World Wars. The basic principles, advanced then,? of blending into the background, use of disruptive patterns to disguise shape and form, and mimicking of background objects -? have remained largely unchanged, textbooks in biology and the visual sciences illustrated by beguiling photos of leaf-like moths, twig-like caterpillars and oddly striped frogs. Surprisingly, however, many of the fundamental principles of camouflage remain untested and, importantly, are stated in language that predates modern computational theories of vision. Our aim is to use modern computational theories of vision to understand the design of animal camouflage, as seen by both humans and animal predators. The great advantage of a computational approach is that it is explicit about the mechanisms of perception and cognition of the human or animal viewer, and so sufficiently precise to generate testable predictions. Of great significance to biologists too, such models can be adjusted to cater for animals with different visual systems from our own. If we are interested in why a moth has a particular colour pattern, we need to understand how its bird predators would see that pattern, and birds not only have a richer colour world than humans (they can see ultraviolet light, for example) their acuity and sensitivity to contrast differs from us. We focus on the two major forms of camouflage, background matching or blending, and disruptive coloration, using computer models and experiments on humans in the lab and wild birds in the field. Bringing the computational neuroscience of vision to biology has clear benefits, but the flow of ideas is not one-way. Because visual systems have evolved to solve real-world problems, of which 'camouflage breaking' is one, then many design features of human vision should be explicable with reference to the ecology of early humans and other primates. Just as we seek to modernise the biological study of coloration through infusion of the theory and technology of computational neuroscience, so too we wish to free the latter of the (usually unrecognised) constraints of modelling the world through human eyes.

Technical Summary

We will develop a computational theory of animal camouflage, with models specific to the visual systems of birds and humans. Birds, because many spectacular examples of camouflage come from insects, and so we must understand their coloration with respect to the vision of their major predators. Humans, because of the fundamental interest, from psychology and computer science, in visual search. Previous research has highlighted key differences in the visual systems of birds and humans, but search for cryptic targets against complex natural backgrounds is a task which both visual systems have surely evolved to perform efficiently. Assessing whether the different designs of the bird and primate eye, and neural architecture, have favoured different solutions to this common problem is of fundamental interest. We focus on the two major forms of camouflage, background matching and disruptive coloration. The former will be addressed using a model of spatiochromatic differences to quantify the conspicuousness of cryptic targets. The predictions will be tested with experiments on humans and wild birds in the field and lab. Disruptive coloration can be distinguished from background matching because it acts against object recognition rather than detection. We propose that several mechanisms may be exploited in various types of coloration. First, the outline of the animal may be disguised by high contrast patches at the body's edge, the salience to edge detectors in the predator's visual system creating false contours that break up the shape of the animal. The second way in which disruptive patterns may be beneficial is in disguising otherwise conspicuous body parts, such as eyes and limbs. Finally, there may be disruptive effects even when patches aren't at the body edge, through untested effects of 'visual crowding' or distraction of attention. Disruptive coloration will be investigated through a different class of model, namely object recognition models from Computer Vision.

Publications

10 25 50
publication icon
Allen W (2013) The evolution and function of pattern diversity in snakes in Behavioral Ecology

publication icon
Allen WL (2011) Why the leopard got its spots: relating pattern development to ecology in felids. in Proceedings. Biological sciences

publication icon
Cuthill I (2010) Animal camouflage: biology meets psychology, computer science and art in International Journal of Design & Nature and Ecodynamics

publication icon
Cuthill IC (2009) Coincident disruptive coloration. in Philosophical transactions of the Royal Society of London. Series B, Biological sciences

publication icon
Espinosa I (2014) Disruptive colouration and perceptual grouping. in PloS one

publication icon
Scott-Samuel NE (2011) Dazzle camouflage affects speed perception. in PloS one

 
Description Providing the first unequivocal experimental evidence for a battery of camouflage mechanisms that have either been assumed to operate, without proof, or for which evidence is equivocal. The power of our evidence lies in (i) experiments showing similar effects in humans and, despite their very different colour vision, birds, (ii) combining field experiments with tightly controlled lab experiments, and (iii) testing the predictive power of different, physiologically plausible, models of visual perception. Results include:
-- The first evidence that 'disruptive camouflage' works by fooling contour (edge) capture mechanisms in low-level vision, whether the viewers are birds or humans.
-- Evidence that symmetrical coloration decreases the effectiveness of camouflage for insects under predation by birds, just as symmetry breaks camouflage for human viewers.
-- The first test of the theory, proposed 100 years ago, that body parts can be concealed by 'coincident disruptive coloration', using colour to blend one body part with another.
Exploitation Route We have taken the findings forward ourselves, under further BBSRC-funded grants. Also, we have developed contacts with the defence sector, receiving funding from QinetiQ, the defence research company, and the UK government (DSTL - the Defence Science and Technology Laboratory).
Sectors Aerospace, Defence and Marine

 
Description In terms of pure science, increasing adoption nationally and nationally of the methods for analysing colour and pattern in evolutionary and behavioural ecology. In terms of impact outside of science: first approach from the defence sector, interested in applications of our (until then animal) camouflage research, in 2008 led to a CASE studentship through EPSRC with QinetiQ, the international defence industry company, as the partner. This led to a contract with complete funding of two PhD students by QinetiQ (value £130k), to develop fast-throughput screening of camouflage effectiveness, and a £100k contract with DSTL (the government's Defence Science and Technology Laboratory) to evaluate dynamic camouflage. Both collaborations are ongoing.
First Year Of Impact 2008
Sector Aerospace, Defence and Marine
Impact Types Economic

 
Description BBSRC SWDTP studentship
Amount £92,000 (GBP)
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 09/2012 
End 09/2016
 
Description BBSRC responsive mode
Amount £79,521 (GBP)
Funding ID BB/J002372/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 09/2012 
End 10/2015
 
Description Commercially funded studentship
Amount £132,000 (GBP)
Organisation Qinetiq 
Sector Private
Country United Kingdom
Start 09/2012 
End 09/2015
 
Description Community Outreach talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact PI gave a University of Bristol Community Outreach talk in 2008. "Animal Camouflage through Animal Eyes".

Considerable audience interest and requests for further information.
Year(s) Of Engagement Activity 2008
 
Description Discover Science display 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact An interactive public demonstration of animal camouflage, called "Hide from a hungry predator", over three days at Bristol's main shopping centre, as part of Discover Science.

Considerable public interest and requests for information. Inquiries about degrees at the University of Bristol from, school pupils (both for Biology and Psychology).
Year(s) Of Engagement Activity 2009
 
Description Exhibit on animal vision at Explore@Bristol 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact One of the PIs was the main advisor for an exhibit on animal colour vision at Explore@Bristol is Bristol's (commercial) interactive science centre, aimed at the general public and children in particular (www.at-bristol.org.uk/). The exhibit was in place for 5 months.

Lots of questions and interest from the public. Mentioned in inquiries about degree courses at the University of Bristol (both Biology and Psychology).
Year(s) Of Engagement Activity 2008