Understanding how an animal camouflages helps to understand the neurological mechanisms used by the visual system to generate images and, since the beginning of the 20th century, has interested artists, naturalists and the military for very different reasons.
Since he was a child, the ophthalmologist at the Hospital Universitario del Henares (Madrid) Julio González Martín-Moro has been attracted to the optical tricks that species use to go unnoticed and whose study helps to unravel the neurological mechanisms involved in the processing of images, hence the related to your medical specialty.
In addition to this search for basic knowledge, camouflage applications have so far been limited to the military field.
The first approach was made by the American painter Abbot Thayer
Although Darwin made some reference to the subject, the truth is that the first scientific approach to the problem was made by the American painter and naturalist Abbot Thayer (1849-1921).
He was the first to describe the reason why many animals have a dark back and a light belly.
Thus, the prey cancels its shadow and reduces the probability of being detected, since "the entire visual system is designed to look for the edges of objects," explains the ophthalmologist.
Similar to a photo editor
It works like a photo editor's contrast-enhancing tool: when a ganglion cell (retinal neurons that make up the optic nerve and connect the eye to the brain) is stimulated, that stimulated cell inhibits neighboring ganglion cells. This enhances the contrast of the image.
There are many optical illusions that are based on this mechanism. For example, the classic optical illusion of the chessboard in which two squares colored with the same shade of gray take on different appearances depending on whether they are located in an illuminated or shaded area.
In order not to be seen, many marine animals are transparent, others change color such as cuttlefish and some even disguise themselves using objects from the environment -the decorator crabs that insert environmental elements (algae, anemones or pebbles) into their exoskeleton to hide themselves. -.
There are three strategies that are especially important: cryptosis, disruptive coloring, and countershading. In the first case, the animal tries to merge with the environment adopting a luminance, color and texture similar to those of the environment, and in the second case it divides the body artificially by means of high contrast bands that rival the real edges of the animal.
Countershading or countershading, one of the most used strategies
Finally, the countershading or countershading mechanism -described by Thayer in 1896- is present in a large number of animals and consists of “trying to cancel out the shadows because they are a very important monocular track in the perception of volume”, explains the Hospital doctor from Henares.
It is not uncommon for a painter to be the first to intuit this mechanism, because the shadow is one of the tools that the visual system uses to give objects volume, and this is precisely one of the most important elements used. by painters to make a two-dimensional object appear three-dimensional.
Thayer noticed that many animals use this trick in reverse. As in nature the main light source is the sun, the upper part of the objects is illuminated, while the lower part is in shadow.
If the animal is colored in reverse (dark back and light belly), the shadow is canceled and the animal flattens and becomes more difficult to detect.
Uniforms of soldiers, military ships ...
Since the beginning of the century, camouflage mechanisms have also interested governments to apply them, for example, in the design of soldiers' uniforms or in the paintings of ships.
During World War I, the English and American governments decided to paint the ships following highly contrasting geometric patterns.
This design is called "motion dazzle". It is not camouflage in the strict sense because it does not hide the object, but it is believed that it can hinder the observer's ability to perceive movement.
The aim therefore was to mislead the torpedo boats of the German ships.
"Motion dazzle" technique on an allied ship during World War I. Photo from Wikipedia (copyright free).
In any case, adds the ophthalmologist, it has never been fully demonstrated whether these types of techniques really worked effectively on ships.
Some modern experiments suggest that high speeds are required for motion dazzle to work.
In fact, at the end of World War I, the English Admiralty analyzed the matter and did not reach any conclusion.
The certain thing, affirms González, is that the boats painted following the “motion dazzle” had been more attacked than the boats painted in a conventional way, but they had been less sunk ”.
"The explanation may lie in the fact that the 'disguised' ships were also the heaviest, making them 'easier to see but more difficult to sink'.
This bias made objective analysis impossible. In World War II, technological advances (the development of radar) made this strategy lose its meaning and the "motion dazzle" disappeared from ships, concludes the ophthalmologist.Ecoportal.net
Contrasombra, a camouflage technique used by antelopes. Photo Julio González Martín Moro
(For more information click on the following link: http://www.ncbi.nlm.nih.gov/pubmed/26560168#)
Photo: Singapore. The mime octopus uses special camouflage techniques. EFE / How Hwee Young