Counter shaded animal patterns: from photons to form
Lead Research Organisation:
University of St Andrews
Department Name: Psychology
Abstract
Many different kinds of animals have camouflaged bodies. In many cases the pattern of colouration features a darker skin, or fur, on the surface of the body that is closer to the sun, and lighter shading on the other side. For example, fish are often dark along their backs and light along their bellies. The same is true for many other animals for example deer, birds, lizards and many insects. This pattern of colouration is known as 'counter-shading'. In this project we aim to understand how counter-shading might provide a useful source of camouflage for animals, and why it has evolved. Does it make them harder to detect, or is their apparent shape, as perceived by a potential predator, changed by this form of colouration? Even a small advantage in being more difficult to detect would enhance the animal's chances of survival, and increase the liklihood of its passing that colouration advantage on to the next generation. There are two ways in which this pattern of colouration might have evolved in order to make an animal harder to detect. First, the animal may simply be trying to match the background. When viewed from above the animals back is darker and matches the ground, and when viewed from below its lighter underbelly matches the sky, so the camouflage could be simply an attempt at background matching. Second, the patterning could represent an attempt to minimise the shading across its surface, so that it appears flatter than it actually is. We know from research in human vision that the shading on the surface of an object helps us to perceive the 3-dimensional (3D) shape of the object (called shape-from-shading). This explains how we can perceive 3D objects in black and white photographs, even though the photograph is actually just a flat surface covered with varying amounts of black ink. So, counter-shading may have evolved in order to confuse these shape-from-shading processes in the brain. A perceptually 'flatter' prey animal may be more difficult to see, or less desirable to eat. The first stage of our project will be to examine counter-shading on prey animals in detail. On one has ever measured the exact patterning on animals and tested to see if the patterns found match the pattern that would be expected for each of the explanations given above. We will measure the 3D shape of individual animals, and their counter-shading. Using the measurements, we will create 3D computer models of animals and their shading. In theoretical studies, we will develop mathematical models that predict what patterns of counter-shading would be ideal for hiding the animal. We will then be able to test these predictions by comparing with the physical measurements. Our computer simulations will show us what patterns of shading are most helpful in hiding an animal. In the second stage of the project, we will test whether the 'most helpful' patterns are actually harder to detect. We will use humans and birds as observers in perceptual experiments that test whether the best shading patterns allow a prey animal to remain hidden for longer. We start by studying humans, because a great deal is already known about shape-from-shading in the human visual system. We also test birds, because their brains are organised rather differently, yet given the frequency of counter-shading in prey, one would predict that non-mammalian predators should also be fooled by this form of camouflage. Finally, we can take what we learn from these simulations and test the results in the real world. By attaching treats to printed cardboard tubes that are distributed around a real outdoor environment, we can see how quickly the tubes are found by wild birds. If the tubes are taken less quickly then we can assume that the shading is much better camouflage. At the end of our project we expect that we will be much closer to an explanation of why counter-shading has evolved in many types of animal.
Technical Summary
Many species are counter-shaded: the dorsal surface is darker than the ventral. It has been proposed that counter-shading offers the animal camouflage. There are two potential accounts of its evolution: (i) counter-shading enables the animal to match its background: when viewed from above the dorsal surface is darker and matches the ground, when viewed from below its lighter ventral matches the sky. (ii) Counter-shading is self-shadow concealment. The image of a 3D uniform coloured object will exhibit a shading pattern, determined by its shape and the light-source direction. Visual shape-from-shading brain processes allow humans to perceive 3D shape even though the retinal image is 2D. A counter-shaded animal disrupts the pattern of shading coming from the light-shape interaction. In the extreme, the shading could cancel out, impeding detection of 3D shape and affecting visibility. Using calibrated cameras we will quantify counter-shading in animals and develop mathematical models to test whether the observed patterns match those expected for the hypotheses above. The models will predict which patterns of shading are best suited to hiding the animal. In laboratory experiments, we will test how well optimal counter-shading patterns fool human visual systems, to probe the details of counter-shading processing. We will also test using bird visual systems, to examine the generality of success of the counter-shading strategies. Finally, field studies will provide the ultimate test: whether the optimal shading patterns from our simulations do improve concealment from birds in natural lighting environments. Our project will determine why counter-shading has evolved in diverse species and the extent to which mammalian (human) and bird visual systems possess visual mechanisms sensitive enough to detect prey despite theoretically optimal counter-shading.
Planned Impact
Companies/public sector bodies [a] This work has potential commercial application, although these lie downstream of the current application. Shape from shading provides low-level cues to structure for simple brains, consequently our findings should be of interest to those involved in developing artificial vision systems. Further, understanding how shading can hinder detection may allow use of shading to enhance detection for reasons of safety (overhead power lines viewed from aircraft) or information transfer (effective design of roadside signage). We will invite contacts from defence company QinetiQ and the Defence Science and Technology Laboratory (Dstl), to discuss our results near the end of the project. [b] One of the first aims of the grant is the extension of a stereoscopic photogrammetry system to utilise calibrated cameras - enabling the recovery of accurate spatial and chromatic information. This system would enable the accurate reconstruction of 3 dimensional scenes, giving accurate colour and distance information. Such a system would be very useful in the human factors industry, for example facilitating the assessment of the visibility of warning systems. Cameras calibrated by Dr Lovell are already used by Railtrack to assess railway sign and signal visibility. [c] A further stage in the development of the photogrammetric scanning system is the calibrated recovery of surface reflectance and the estimation of the smoothness of the object (shiny, matte, rough etc). Such a system would be very useful to those in the game development and film special effects industries attempting to render scenes that appear realistic. Methods and activities We plan to establish a website sharing the 3D scans made of various countershaded animals. These scans would be useful to academics interested in further examining pigmentation patterns and camouflage. The existence and utility of the site will be advertised to the community via our conference presentations, journal publications, and by posting to relevant email lists and user groups. We have close links with several museums (Hunterian, Glasgow, Bell-Pettigrew, St. Andrews, Explore@Bristol, Bristol) with 1 exhibit already in place (Hunterian). This will be augmented, and new exhibits installed in the other museums. We will prepare (and use) portable exhibits for science fairs and festivals. The Applied Vision Association (AVA) provides a useful platform for the presentation our findings to academics in related fields and to industrial partners. We will budget for two people to attend one AVA meeting each (Xmas or Annual Easter) near the end of the project.
Publications
Vinther J
(2016)
3D Camouflage in an Ornithischian Dinosaur.
in Current biology : CB
Penacchio, O.
(2013)
Countershading camouflage: using light for concealing 3D information
in Perception
Cammack P
(2016)
Depth perception in disparity-defined objects: finding the balance between averaging and segregation.
in Philosophical transactions of the Royal Society of London. Series B, Biological sciences
Penacchio, O.
(2015)
Does countershading contribute to visual camouflage by concealing 3D shape?
Penacchio O
(2017)
Establishing the behavioural limits for countershaded camouflage.
in Scientific reports
Cuthill IC
(2015)
Flower colour: Gloger's rule isn't just for the birds.
in Nature plants
Penacchio O
(2018)
Is countershading camouflage robust to lighting change due to weather?
in Royal Society open science
Cuthill Innes C.
(2015)
Matching the background: deceptively simple?
in PERCEPTION
Cuthill IC
(2016)
Optimizing countershading camouflage.
in Proceedings of the National Academy of Sciences of the United States of America
Penacchio O
(2015)
Orientation to the sun by animals and its interaction with crypsis.
in Functional ecology
Penacchio O
(2015)
Orientation to the sun by animals and its interaction with crypsis.
in Functional ecology
Cuthill IC
(2017)
The biology of color.
in Science (New York, N.Y.)
Cuthill IC
(2015)
The Oxford Handbook of Perceptual Organisation
Penacchio O
(2015)
Three-Dimensional Camouflage: Exploiting Photons to Conceal Form.
in The American naturalist
Penacchio O
(2015)
Visual discomfort and the spatial distribution of Fourier energy.
in Vision research
Penacchio O
(2015)
Visual search using realistic camouflage: countershading is highly effective at deterring search.
in Journal of Vision
Description | We achieved all our original objectives, namely: (1) We measured, for the first time, both the surface reflectance ('colour') and 3D shapes of a range of counter-shaded caterpillars. Interestingly, the shapes of counter-shaded caterpillars seem adapted to minimising changes in appearance as a result of changes in lighting. That is, shape and colour are co-adapted for camouflage. (2) We developed the first mathematical model of optimal counter-shading for concealment of 3D form, using light-path modelling techniques from computer vision. This led to publications on how camouflage should relate to habitat type, time of day, season, latitude and orientation: a predictive toolkit that biologists can exploit to test theories about these ecological characteristics should affect both evolution and behaviour in relation to predation risk. (3) We carried out the first tightly controlled experiments on how deceptive shading patterns alter the perceived shape and visibility of prey. We carried out the experiments on both humans and starlings, the similar results suggesting that the shape-from-shading cues used to recover object identity information are similar across both these taxa, despite their rather different visual systems. (4) We showed that counter-shaded prey, coloured in line with predictions derived from (2) above, are harder to detect by birds under field conditions in a natural environment, but that this is (as predicted) strongly dependent upon lighting conditions. This is the first rigorous experimental test of counter-shading theory, possible only because of our combination of mathematical modelling of light environments with the ability to model colours as perceived by other species. |
Exploitation Route | We have taken the findings forward ourselves, under further BBSRC-funded grants. Also, we have developed contacts with the defence sector (Dstl, QinetiQ) as described under Narrative Impact. |
Sectors | Aerospace, Defence and Marine,Education,Environment |
Description | The primary goals of the research comprised pure science, but the results have scientific impacts beyond the specific outcomes detailed elsewhere. Counter-shading is in all the undergraduate biology textbooks as an example of the power of natural selection to shape animal design; it is in all the undergraduate psychology textbooks as an example of how principles of depth perception are reflected in nature. None of this has been backed up by hard evidence until now: we feel the results are definitive and synthetic across these, traditionally separate, disciplines. In terms of impact outside of science, we have worked in two directions (as outlined in our original Pathways to Impact document): education and the defence sector. Animal coloration is an attractive topic with which to engage schoolchildren in both biology and psychology, and illustrate career options in these fields and (because our modelling brings in physics and computation) STEM subjects more generally. We have given talks at schools, to pupils from pre-GCSE to 6th form, and developed displays for public science festivals. As a form of military camouflage with a venerable history (countershading was used on land vehicles in WW1 and both submarines and aircraft in WW2), we have also discussed our work with contacts in the defence sector (the government's Defence Science and Technology Laboratory and QinetiQ, the international defence industry company). We also organised a session within an annual meeting of the Applied Vision Association in Nottingham in early 2015, and a one-day satellite meeting of the European Conference on Visual Perception, in Liverpool in 2015 ("CamoCon 2015") to which representatives of both Dstl and QinetiQ were invited. We also visited QinetiQ's headquarters in Farnborough, at which representative of Dstl were again present. Discussions of how our research might be applied, or taken further, are ongoing. |
First Year Of Impact | 2008 |
Sector | Aerospace, Defence and Marine,Education,Environment |
Impact Types | Cultural,Economic |
Description | Applied Vision Association postdoc travel award (Penacchio) |
Amount | £700 (GBP) |
Organisation | Applied Vision Association |
Sector | Private |
Country | United Kingdom |
Start | 05/2016 |
End | 06/2016 |
Title | Data from: Optimizing countershading camouflage |
Description | |
Type Of Material | Database/Collection of data |
Year Produced | 2016 |
Provided To Others? | Yes |
Title | Data from: Orientation to the sun by animals and its interaction with crypsis |
Description | |
Type Of Material | Database/Collection of data |
Year Produced | 2015 |
Provided To Others? | Yes |
Title | Data from: Three-dimensional camouflage: exploiting photons to conceal form |
Description | |
Type Of Material | Database/Collection of data |
Year Produced | 2015 |
Provided To Others? | Yes |
Description | Modelling collaboration with Xavier Otazu |
Organisation | Autonomous University of Barcelona (UAB) |
Department | Department of Computer Science |
Country | Spain |
Sector | Academic/University |
PI Contribution | Collaboration with Xavier Otazu and his group from Autonomous University, Barcelona, on computational modelling. He is working with us on ideas that emerged from our grants on camouflage and aposematism. We have hosted him and his group for sabbatical trips to work with us in St. Andrews. |
Collaborator Contribution | We have been exposed to, and training in, neural computational modelling methods and given a 'modellers perspective' understanding of the kinds of biological and psychological information needed to develop a successful computational model. |
Impact | Multi-disciplinary: biology, psychology, computer science, neuroscience. |
Start Year | 2016 |
Description | Pennacchio collaboration with Sonke Johnsen |
Organisation | Duke University |
Country | United States |
Sector | Academic/University |
PI Contribution | Olivier Pennacchio is using work from projects on camouflage and animal warning signals and developing a collaboration on under-water camouflage with Sonke Johnsen. |
Collaborator Contribution | Sonic Johnsen is an expert on under-water camouflage and interested in our theoretical work. |
Impact | non yet. |
Start Year | 2016 |
Description | ViiHM network: Visual image interpretation in humans and machines |
Organisation | University of Birmingham |
Department | School of Psychology Birmingham |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | EPSRC funded network, I am a member. |
Collaborator Contribution | A network funded by EPSRC -- Schofield at Birmingham is the PI |
Impact | None yet |
Start Year | 2014 |
Description | Cuthill, I.: Cafe Scientifique presentation on animal camouflage (Bristol) |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | Part of a new series of science engagement talks ('A Pint of Science') for the general public (although some students attended too). |
Year(s) Of Engagement Activity | 2015 |
URL | https://pintofscience.com |
Description | Cuthill, I.: Conference (Royal Society) |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | Cuthill: co-organiser (with H. Rowland, T. Pike) of Royal Society Theo Murphy international scientific meeting "When sense take flight: the evolution, development, mechanisms and function of avian senses." |
Year(s) Of Engagement Activity | 2014 |
URL | https://royalsociety.org/events/2014/avian-senses/ |
Description | Cuthill, I.: Conference on camouflage (Liverpool) |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | Cuthill: co-organiser (with N. Scott-Samuel) of CamoCon 2015, satellite meeting of the annual European Conference on Visual Perception, Liverpool, UK. |
Year(s) Of Engagement Activity | 2015 |
Description | Cuthill, I.: School visit (Birmingham) |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Schools |
Results and Impact | Talks to (i) ca. 220 GCSE pupils on biomimicry and (ii) ca. 40 lower 6th formers on careers in biology, at large inner-city comprehensive. |
Year(s) Of Engagement Activity | 2015 |
Description | Cuthill, I.: School visit (Bristol) |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Schools |
Results and Impact | Talk on careers in biology to lower 6th form at local school. |
Year(s) Of Engagement Activity | 2015 |
Description | Cuthill, I.: Talk on animal camouflage to school (Taunton, Somerset) |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Schools |
Results and Impact | Talk on animal camouflage in biology to major regional school. |
Year(s) Of Engagement Activity | 2014 |
Description | Cuthill, I.: Talk to general public on animal camouflage. |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | Invited to run a 'cafe scientifique' for the general public as part of a British Science Association series in Bristol, Bath and NE Somerset. |
Year(s) Of Engagement Activity | 2015 |
Description | Explorathon 2016: Harris lab exhibit at this European Researchers night event, highlighting research activity on vision. |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Part of a European Researchers Night event, showing academic research taking place at the University of St. Andrews |
Year(s) Of Engagement Activity | 2016 |
Description | Explorathon 2017: Harris lab exhibit at this European Researchers night event, highlighting research activity on vision. |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Explorathon 2017: Harris lab exhibit 'Vision: more than meets the eye' at this European Researchers night event, highlighting research activity on vision. |
Year(s) Of Engagement Activity | 2017 |
URL | http://www.explorathon.co.uk/standrews |
Description | Harris 2015 Article in The Conversation |
Form Of Engagement Activity | A magazine, newsletter or online publication |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Public/other audiences |
Results and Impact | We published an online article describing two of our recent publications on visual camouflage. |
Year(s) Of Engagement Activity | 2015 |
URL | https://theconversation.com/sunscreen-or-camouflage-why-so-many-animals-have-dark-backs-and-pale-bel... |
Description | Harris St Andrews Open Assoc 2015 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | Talk on vision as part of the St. Andrews University Open Association lecture series, aimed at the general public from Fife and the surrounding area. There was an extended question session, where there were many questions, linked in particular to visual deficits and disorders and how our science informs these areas. |
Year(s) Of Engagement Activity | 2015 |
Description | Harris Sutton Trust Lectures |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Schools |
Results and Impact | The talk was on vision, part of a Summer School for disadvantaged teenagers, organised by the Sutton Trust charity. Participants were surprised that vision and perception are part of the psychology and neuroscience curricula but were interested and engaged in the topics. |
Year(s) Of Engagement Activity | 2007,2009,2011,2015 |
Description | Harris lab vision exhibit, Fife Science Festival: St. Andrews Open Day |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | Demos and hands-on lab activities from the Harris lab including 3D vision and motion perception, vision and driving, visual camouflage. The activities were popular with all age-groups, from small children, to parents, and older adults. Several people commented that they didn't know vision was linked to neuroscience and psychology, as well as optometry and physics. |
Year(s) Of Engagement Activity | 2010,2011,2012,2015 |
Description | Harris talk at Cafe Scientifique, Dunkeld and Pitlochry , Scotland |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Harris talk at Cafe Scientifique, Dunkeld and Pitlochry , Scotland. Talk was primarily on basic 3D vision, but included discussion of how camouflage and animal patterning affects predation. |
Year(s) Of Engagement Activity | 2016 |
Description | Harris talk at Perceptual Representation of Illumination, Shape & Material Conference 2016 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Industry/Business |
Results and Impact | Invited talk to EU postgraduate training network and industrial collaborators. Title: Counter-shading camouflage: shape from shading in nature. |
Year(s) Of Engagement Activity | 2016 |
Description | Lovell Cafe Scientifique 2015 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Talks entitled 'Cafe Science Extra - Camouflage: Hiding in Plain Sight with Dr George Lovell'. George talked about our work on animal camouflage and how animals patterning evolves to beat the visual systems of predators. |
Year(s) Of Engagement Activity | 2015 |
Description | Penacchio and Harris lab: Public engagement poster: Butterfly World |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | We collaborated with a local attraction, "Butterfly World" by asking them to rear exotic moth caterpillars. We provided them with a public engagement poster to explain the aims of our broader project to the public. Hard to explroe this, as we were not ourselves involved in the presentation. |
Year(s) Of Engagement Activity | 2014 |
Description | Public science event at local School |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Schools |
Results and Impact | Team members from Harris lab took part in participatory event, encouraging children, and families, to think about how animal visual systems are designed to be specifically sensitive to some patterns, and how others may be camouflaged. |
Year(s) Of Engagement Activity | 2019 |
Description | Radio interview for BBC World Service ("Science in Action") by Innes Cuthill |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Media (as a channel to the public) |
Results and Impact | Innes Cuthill did a radio interview for the BBC World Service's "Science in Action" program, explaining the results in Cuthill et al. 2016 (PNAS: doi: 10.1073/pnas.1611589113). My piece comes about 21 minutes into the programme. |
Year(s) Of Engagement Activity | 2016 |
URL | http://www.bbc.co.uk/programmes/p04d8k62 |
Description | Visual Perception in Humans and Animal Camouflage, Explorathon 18 exhibit |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Visual Perception in Humans and Animal Camouflage, Interactive presentation at science fair, Explorathon 2018, held at Dundee Science Centre (science museum). |
Year(s) Of Engagement Activity | 2018 |