Category Archives: nature

dog vision

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I just read an article in The Daily Mail that says that most people think dogs do not have colour vision. The article then goes on to say that Russian scientists have proved that dogs do have colour vision. It seems to me quite accepted that dogs are dichromats – that is they have two types of light-sensitive cells that contribute to colour vision in their eyes. We – humans – are trichromats because we have three such cells. It turns out that the one that is missing – in dogs – is such that dogs’ colour vision is rather like that of a human who has red-green colour blindness. The image below shows how the spectrum looks to a trichromatic human and a dichromatic dog.

dog_vision

As you can see, dogs can bee blues and yellow but have difficulty discriminating between colours in the red-green part of the spectrum. So I am not sure what the fuss is about with the Daily Mail article. After all, everything in the Daily Mail is true!! See http://www.youtube.com/watch?v=5eBT6OSr1TI if you don’t believe me.

eyes change colour?

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reindeer

I didn’t realise how sophisticated reindeers are. It turns out they have two layers of fur to help them keep warm, are able to shrink the pads on their hooves to give then better grip, and can detect ultraviolet light which enables them too see in very dim light. And it also turns out that their eyes can change colour in winter so that their vision is more sensitive. Reindeers, like cats, have a reflective layer behind the retina (which is the inside of the eye ball where all the light-sensitive cells are) that helps them to see in dim light. This is why, if you see a cat at night, you might see the eyes shining; you are seeing light being reflected back at you from the cat’s tapetum lucidum (which is the technical term for the layer behind the retina). The light that shines back in most animals with this layer is golden but in reindeer it apparently shifts to blue in the winter. The shift to blue allows more light to be scattered and improves the vision of the animal.

The full paper can be read in the Proceedings of the Royal Society.

skin colour and personality

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Excellent article based on an extract from Nina Jablonski’s book “Living Colour: The Biological and Social Meaning of Skin Colour” about early ideas about the relationship between skin colour and personality.

The first scientific classification of humans, published by Carl Linnaeus in 1735, was simple and separated people into four varieties by skin colour and continent. Later, Linnaeus added that Europeans were white and “sanguine,” Asians were brown and “melancholic,” Native Americans were red and “choleric” and Africans were black and “phlegmatic”. Of course, these racist pronouncements were based on prejudice and myth and little, if any, factual information. Nevertheless, these ideas led to an intellectual foundation for racism. Immanuel Kant, was the first to formally define races and in 1785 classified people into four fixed races, which were arrayed in a hierarchy according to colour and talent. It sounds like a really interesting book on anthropology and I’ll order a copy tomorrow. I’ll try to remember to comment when I have read the full book.

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Four temperaments is a proto-psychological interpretation of the ancient medical concept of humorism and suggests that four bodily fluids affect human personality traits and behaviors. The temperaments are sanguine (pleasure-seeking and sociable), choleric (ambitious and leader-like), melancholic (introverted and thoughtful), and phlegmatic (relaxed and quiet).

Eye colour and trust

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According to a recent study eye colour plays a role in deciding how trustworthy others will think you are. Researchers simply asked a group of people to rate the trustworthiness of male and female faces. It was found that a majority of people found people with brown eyes to appear more trustworthy. This was true for both sexes but particularly so for men.

nuBz6lu

But it turns out that it is face shape that is more important and eye colour is a major factor because brown-eyed people tend to have certain facial characteristics. For the original story see here.

chicken colour vision

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Most humans are trichromatic; that is, our colour vision is mediated by three types of light receptor in our eyes. These receptors are known as cones and the three types have peak sensitivity in different parts of the colour spectrum. We sometimes refer to these as LMS cones because of their peak sensitivity at long-, medium- and short-wavelengths light.

Some people (men, in the main) are colour blind and this is because they are anomalous trichromats (they have three cones but the spectral sensitivities are less optimal than they should be or they are dichromats (they are missing the L, M or S cone types). But what about other species?

Most mammals are dichromats including dogs and cats. However, many fish and birds have better colour vision than do we humans. I just came across an article that reports that chicknes have five cones compared with our three. The research has been conducted the Washington University School of Medicine in St. Louis (USA). It is suggested that birds often have more cones than we do because they descended directly from dinosaurs and never spent any part of their evolutionary past living in the dark.

special females

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Our colour vision results from the fact that our eyes contain three types of light-sensitive cells or cones that have different wavelength sensitivity. Some people (called anomalous trichromats) are colour blind and this is usually because one of their cones is mutated and has a different wavelength sensitivity compared with those in so-called normal observers. Colour-blind is a misnomer really because anomalous trichromats can still see colour; they just have less ability to discriminate between colours than normals. Some people are missing one of the cone classes altogether and are referred to as dichromats; they have even poorer colour discrimination but can still see colour. Only monochromats are really colour blind and they are extremely rare.

For a long time I have known that some females have four cones classes (this makes them tetrachromats). Dr Gabriele Jordan, a researcher at the Institute of Neuroscience (Newcastle University) has spent the last 20 years working on human colour vision. She has discovered that tetrachromatic females exist and that although this gives them the potential for colour discrimination much better than normal trichromats in practice most have normal colour discrimination. However, in a recent report she has found a tetrachromat who really does have enhanced colour discrimination. This is really exciting news!

The report in the Daily Mail suggest that a functional tetrachromat could be able to see 99 million more hues than the average person. Personally I am skeptical of this claim even if, as I suspect, it means 99 million more hues than the average person. The number of colours that an average person can see is debatable but I think may be about 10 million (see my previous blog post).

jaws

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“Wearing a light blue wetsuit that matches the colour of the sea will make you less likely to become the victim of a shark attack, according to researchers.
Sharks are completely colour blind and only see things clearly if they are mostly light or dark, scientists have claimed.”according to the Daily Mail.

This does not make a lot of sense – if sharks are colour blind then it wouldn’t matter what colour you wear. But later in the article the point is put better by Professor Nathan Hart, from the University of Western Australia: ‘It’s the high contrast against the water rather than the colour itself which is probably attractive to sharks. So you should wear perhaps more muted colours or colours that match the background in the water better.’

Apparently sharks really are monochromats – so colour blind in the popular understanding of the word – and so it’s really a case of matching the yoru swim suit with the lightness or brightness of the surrounding water. Don’t wear a very bright or a very dark swim suit, in short. Maybe this can lead to better designed swimwear!

what colour is indigo?

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Seems to be a lot of people typing

what colour is indigo

into google. Why all the fuss about indigo?

In case you are one of those people I can tell you that in the spectrum indigo was generally considered to be associated with wavelengths in the range 420nm – 450nm though many would argue that it is not in the spectrum at all and that light below about 450nm is considered to be violet. Have a look at my earlier post about why indigo is generally not considered to be in the spectrum by modern colour scientists.

In terms of RGB (sRGB for the techies) it can be approximated as R=75, G=0, B=130 and this looks like this:

Though of course, the RGB on-screen representation is not the same colour as the indigo in the colour spectrum since every colour in the spectrum is outside the gamut of your RGB display and therefore cannot be properly shown.

The word indigo is named after the blue colorant obtained from plant indigofera tinctoria.

oldest work of art ever

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I previously wrote about the finding of the oldest cave painting in the UK which was a 14,000-year old painting found in a cave in South Wales. You can read about that post here. Of course, the oldest cave paintings in the world are perhaps 30,000 years old; probably the Chauvet caves in France. Today, however, I read of a new finding: these are six paintings of seals that have been found in caves on the coast of Spain, about 35 miles east of Malaga, and thought to be about 42,000 years old.

The article claims that these paintings of seals are the oldest known works of art in the world. But are they? In 2000 the BBC reported that archaeologists in Zambia uncovered evidence that early humans used paint for aesthetic purposes far earlier than previously thought. The team found pigments and paint grinding equipment believed to be between 350,000 and 400,000 years old. The oldest pigments previously found were 120,000 years old.

red makes you eat less

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Yesterday was the first lecture in my module (Colour: Art and Science) at the University of Leeds. In this module I look at colour from a multi-disciplinary perspective covering art, design, physics, history, philosophy, neuroscience, advertising and branding – all perspectives that are needed to understand colour or are strongly influenced by colour. Towards the end of the module I look at colour in branding and advertising and look at the effects that colours have on people’s behaviours and emotional states. One of the frustrating things about it though is that there is a lack of high-quality research about this. In fact, I would go so far as to say that there is more nonesense written about colour (in books and on the internet) than almost any other topic I know!

Take the effect of colour on appetite. Lots of websites and books will tell you the same thing. Red stimulates appetite and this is one reason, for example, why it might be used in MacDonalds’ interior colour scheme. On the hand, blue inhibits your appetite; one reason for this is often stated as being that blue foods are quite rare and therefore we are predisposed to not want to eat blue foods (though what about blueberries!!). But when people write this, how many of them have actually done any research or read any research about these effects? That’s what I mean about nonesense; people write it because they heard it somewhere or imagined that it might be true. Last week I came across some research on the effect of colour on appetite. In this research, published in the Journal of Appetite, and jointly carried out by staff from the University of Basel (Switzerland) and the University of Mannheim (Germany) it was shown that participants drank less from a red cup than a blue cup and ate less snack food from a red plate than from a blue plate. In other words, the opposite of what is commonly believed. The point of this is that more serious research needs to be done to explore the effects that colour has; come and do a PhD in my lab and help to rectify that!!

Of course, the research referred to above does not necessarily mean that people would prefer red food to blue food or that people would eat less food in a restaurant decorated in red rather than blue. It is exactly that sort of extrapolation that is partly responsible for all of the misinformation about colour that is everywhere around us. I have to confess that I myself am sometimes responsible for this misinformation since I was talking to the students last year about the appetite-suppressant properties of blue. I need to stop now …. and go and do some more research.