Tag Archives: colour

Squid's eye. Credit: Wikipedia

How cephalopods are masters of camouflage despite seeing in black and white

Squid's eye. Credit: Wikipedia

Squid’s eye. Credit: Wikipedia

Despite having a single type of visual pigment in their retinas, cephalopods can blend with their multi-coloured surroundings easily fooling both prey and predators. This has stricken many scientists as a paradox. Christopher Stubbs, a Harvard professor of physics and astronomy, thinks he has some clues as to how the creatures manage this feat. His research suggests cephalopods might be able to detect colour after all, but in a very unusual way akin to how a digital camera dithers back and forth to create a crisp image.

Example of chromatic aberration in a digital camera. Credit: Creativecow.net

Example of chromatic aberration in a digital camera. Credit: Creativecow.net

Stubbs was spurred to embark on this research by his son, Alexander, who’s a graduate student at Berkely and co-author of the new study. “He chased me down with an idea he’d come up with, and the more we talked about it, the more sense it made,” he said. The starting point was that cephalopods could potentially detect colour by adjusting the focal position to detect different wavelengths of light. These wavelengths could then composite each other to form a colour image of the world.

“To me, what’s really persuasive about this argument is…the pupils in these animals are an off-axis U shape, and that actually maximizes this chromatic signature at the expense of image sharpness. So it actually looks like there’s been selective evolutionary pressure for their pupil shape to maximize this phenomenon,” Prof. Stubbs said.

In other words, octopuses, squids or cuttlefish might be exploiting a physical phenomenon called chromatic aberration. Also known as “color fringing” or “purple fringing”, this common optical pattern occurs when a lens is unable to bring all the wavelengths of colour to the same focal plane or when the colour wavelengths are focused at different positions in the focal plane. What happens is the various colour wavelengths travel at different speeds passing through the lens, resulting in an image that is blurred or has coloured edges (red, green, blue, yellow, purple, magenta).

octopus camouflage gif

Amazing camouflage. Credit: Giphy

Chromatic aberration has plagued digital camera manufacturers for years. But while companies are investing a lot in creating the perfect lens which focuses all wavelengths into a single focal point, cephalopods seem to have evolved this ability to use it to their best advantage.

To understand how the animals might employ chromatic aberration, Chris Stubbs created a computer model of the cephalopod eye similar to his previous calculations made for astrophysical research. These calculations reveal that the animals’ eyes are biologically equipped to see in colours — an elegant mechanism never before encountered, as reported in the journal PNAS.

“People have done a lot of physiological research on the optical properties of lenses in these animals,” he explained. “We wrote some computer code that essentially takes test patterns and moves the retina back and forth, and superimposes that on the image and then measures the contrast.”

“This is an entirely different scheme than the multi-color visual pigments that are common in humans and many other animals. High-acuity “camera style” lens eyes in octopus, squid and cuttlefish represent a completely independent evolution of complex eyes from vertebrates so in some sense we shouldn’t necessarily expect that this lineage would solve problems like color vision in the same way. These organisms seem to have the machinery for color vision, just not in a way we had previously imagined,” added Alexander Stubbs.

physics of colour

What makes things coloured – the physics behind it

It’s hard to image a world without colours simply because they’re all around us. Have you ever wondered, though, where do colours come from? To answer this question, we first have to understand how human colour perception works and how matter physically interacts with light.

What gives colour

physics of colour

Image: Food Navigator

White light is a mixture of all colours, including those that the human eye can’t see. When we say something has colour, what we actually mean is that light of a particular range of wavelengths is reflected more strongly than the light of other wavelengths. How matter behaves in the presence of light, consequently appearing coloured to us humans, depends on a couple of major factors.  First of all — everything is made up of electrons and atoms, but each substance has a different number of atoms and different electron configuration. This way, when light hits matter one or more of the following phenomena happens:

  • reflection and scattering. Most objects reflect light, but some are more reflective than others, like metals. This is directly related to the number of free electrons that are able to pass from atom to atom with ease. Instead of absorbing energy from the light, the free electrons vibrate and the light energy is sent out of the material at the same frequency as the original light coming in.
  • absorption. When there’s no reflection (the object is opaque), then the incoming light source frequency is the same as, or very close to, the vibration frequency of the electrons in the given material. The electrons thus absorb most of the incoming energy, with little or no reflection.
  • transmission. If the incoming light energy is much lower or much higher than that required for the electrons comprising an object to vibrate, then the light source will pass through the material unchanged. This way matter will look transparent to the human eye, such as in the case of glass.
  • refraction. If the energy of the incoming light is the same as the vibration frequency of the electrons in the material, light is able to go deep into the material, and causes small vibrations in the electrons. The vibrations are then passed on from atom to atom, each vibrating at the same frequency as the incoming light source. This makes the light inside the material look bent. Example: a straw in a glass of water.

Light and matter

seeing coloursseeing in colour

Image via Pantone.com

The human eye and brain translate light into colour. Light receptors within the eye transmit messages to the brain, producing the familiar sensation of colour. The retina is covered by millions of light-sensitive cells, some shaped like rods and some like cones, and it’s these receptors that process the light and then send this information to the visual cortex.  Rods are mostly concentrated around the edge of the retina and transmit mostly black and white information. Cones transmit the higher levels of light intensity that create the sensation of color and visual sharpness. These cells, working in combination with connecting nerve cells, give the brain enough information to interpret and name colours.

Think of atoms like bricks in a wall (chemical compound). Imagine throwing a ball into the wall. If the wall is smooth or has sharp corners, the ball may jump back in different directions. However, if the wall is filled with holes, the ball may go through the wall or get stuck in one of the tricky corners, respectively. Same with every surface when light hits it. The surface may reflect the light back; it can absorb light or just let it pass through (transparent things).

This analogy is far from perfect though because light isn’t like a ball. For instance, the light we get to see, called visible light, is only a fraction of the full range of frequencies. A molecule might absorb photons from anywhere across the whole electromagnetic spectrum, from radio waves to X-rays, but it will be colourful only if there is a difference in how strongly it absorbs one visible wavelength over another. As it turns out, this is quite uncommon since most molecules absorb light above the visible spectrum, in the ultraviolet range. So, because electrons in most molecules are bound very tightly, most compounds are white!

Chemical formula or the organic dye indigo. Image: ABC.net.au

Chemical formula or the organic dye indigo. Image: ABC.net.au

Some substances have electrons in the right range of binding strength which makes them suitable to use as dyes. One of the first natural dyes is indigo, commonly used to colour jeans. It derives its colour from a set of three double-bonds at its centre (O=C, C=C, C=O). The problem with indigo and other organic dyes is that it fades away in time because it absorbs energy, instead of reflecting it. In time, bonds break as a result of the damage. Inorganic dyes like pure iron oxide or rust (ochre), however, are lightfast and can last for thousands of years. This is why cave paintings are still visible today!

Lycopene is a bright red carotenoid pigment, a phytochemical found not only in tomatoes but also other red fruits. Lycopene absorbs most of the visible light spectrum, and being red in colour, Lycopene reflects mainly red back to the viewer, thus a ripe tomato appears to be Red. Image: Colour Therapy Healing

Lycopene is a bright red carotenoid pigment, a phytochemical found not only in tomatoes but also other red fruits.
Lycopene absorbs most of the visible light spectrum and reflects mainly red back to the viewer, thus a ripe tomato appears red. Image: Colour Therapy Healing

As a conclusion,  things do not have color by themselves — only when light (energy) hits them, we can see colors. This is precisely why your surroundings appear greyish or downright black when you’re in the dark. Also, remember our eyes can only see a limited range of colours. But dogs, cats, mice, rats and rabbits have very poor colour vision. In fact, they see mostly greys and some blues and yellows, while bees and butterflies can see colors that we can’t see. Their range of color vision extends into the ultraviolet, and in fact, they couldn’t have survived otherwise. Evolution led bees to adapt ultraviolet vision because flowers leave scatter ultraviolet patterns, allowing the insects to easily identify targets and pollinate. But while humans can’t see colours beyond our visible spectrum, the machines we build can. This is what spectrometers are for.

The colour red increases speed and strength of reactions

What can possibly link together speed, strength, and the colour red ? Nope, it’s not a brand new Ferrari – it’s your muscles ! A new groundbreaking study published in the journal Emotion shows that if you see red, your reactions become faster, more powerful, and you won’t even realize it.

Science and sports

Of course, due to the crazy amounts of money that are put in sports these days, one of the first thing that comes to mind is using this advantage to become a better athlete. A brief burst of speed and strength is often all you need to overcome your competition, but scientists warn that the ‘colour energy’ is likely short lived.

“Red enhances our physical reactions because it is seen as a danger cue,” explains coauthor Andrew Elliot, professor of psychology at the University of Rochester and a lead researcher in the field of color psychology. “Humans flush when they are angry or preparing for attack,” he explains. “People are acutely aware of such reddening in others and it’s implications.”

But a threat is a double edged sword, Elliot and coauthor Henk Aarts, professor of psychology at Utrecht University, in the Netherlands argue. Along with the increased qualities, side effects also include “worry, task distraction, and self-preoccupation, all of which have been shown to tax mental resources”.

Good for reactions, bad for your mind

Red has already been proven as counter productive for sustained mental activities, such as studying, for example; it has been shown that students exposed to red before an exam fare slightly worse than those who weren’t.

“Color affects us in many ways depending on the context,” explains Elliot, whose research also has documented how men and women are unconsciously attracted to the opposite sex when they wear red. “Those color effects fly under our awareness radar,” he says.

Testing students’ reactions

The study was conducted by measuring the reactions of students in two experiments.

In the first one, students from 4th to 10th grade pinched and held open a metal clasp. Right before doing so, they read aloud their participant number written in either red or gray crayon.

In the second experiment, undergrads were asked to squeeze a handgrip with their dominant hand as hard as possible when they read the word squeeze on a screen. The word appeared on a blue, gray, and red background.

In both scenarios, red increased the strength significantly, and in the second experiment, it was proven that not only the power, but also the reaction speed was increased. The colours in the experiment were also exactly controled, in terms of hue, brightness, and chroma (intensity) to insure that reactions were not a result of some other variable besides colour.

“Many color psychology studies in the past have failed to account for these independent variables, so the results have been ambiguous,” explains Elliot.

If you ask me, it’s another great example of how the most mundane elements around us, like colour, can have a significant impact on our lives. Hopefully, studies will be continued in this direction so that there will be even a vague method of quantification.

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