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Posts Tagged ‘Color & bare skin’

Ian Woolf of Diffusion Radio just reviewed The Vision Revolution, and you can hear the podcast here (15 minutes in).

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Mark Changizi is a professor of cognitive science at Rensselaer Polytechnic Institute, and the author of The Vision Revolution (Benbella Books).

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I was recently interviewed by Deborah Burnett for the (gorgeous) Professional Lighting Design Magazine. The topic was how to better design lighting to tap into what our eyes are meant to see, and more specifically about understanding this in light of my research that color vision may have evolved for seeing skin coloration signals. Here’s the link to the pdf.

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Here are some more links about color vision and skin.

Mark Changizi is a professor of cognitive science at Rensselaer Polytechnic Institute, and the author of The Vision Revolution (Benbella Books).

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The press release just came out for my simple proposal for harnessing our color vision for better sensing clinical skin color changes of patients, along with some news stories, which can be linked here…

LA Times, Toronto Sun, Forbes, Times Union (and video), Troy Record, BoingBoing, AOL News, Times Colony, Diagnostic Imaging, Ratschlag24, Press Release, and my own SB piece. Also, here’s the paper itself.

This proposal for medicine is a corollary of my research on the evolution of color vision — it’s for seeing emotions and states on the skin of those around us — something you can read about in my book, The Vision Revolution. I have a variety of pieces on the research here.

And here’s a figure that helps summarize the “oximetry” point in the press release…

Mark Changizi is a professor of cognitive science at Rensselaer Polytechnic Institute, and the author of The Vision Revolution (Benbella Books).

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It’s Valentine Day, and children everywhere celebrated friendship and love by giving cards and candy to their friends. In what alien observers must consider one of the most bizarre human customs, these same children were asked to draw lewd pictures of human private parts. You don’t think you or your children participated in this custom? Take a look at the figure below…

valentines heart as human  rump

I thought you might recognize it. It’s the Valentine heart, of course. But what you may have failed to consciously notice – and what gives the alien observers the giggles – is that the Valentine’s heart is not just some arbitrary red double-humped shape. Rather, the Valentine heart is the human rump – the red, engorged, upturned human rump. You’ve seen too many Valentine hearts to believe me at this point – and, sadly, you have probably seen far too few red, engorged upturned human rumps – so I encourage you to make your own field observations and verify.

Because this is a family web site, rather than showing you the flushed upturned rump of a human female, I have placed the flushed upturned bum of one of our close cousins below.

primate rump valentines  day heart

I’m surely not the first to have noticed the rump-like look of the Valentine heart, but I’m surprised how long it took me to notice. You see, I have an uncomfortably tight history with the primate rump – if you do a Google search on primate rump you get ME! Try it. The article of mine that comes up concerns how our primate variety of color vision may have evolved in order to sense skin color changes like those found on bare primate rumps. How could I have missed the Valentine rump? And now that I’ve noticed it, though, I can’t shake it! My wee children exchanged Valentines with their school friends last week, and rather than seeing sweet cards, I can’t help now but see each heart as a case of NSFW anime porn!

The most characteristic symbol of Valentines – symbolic of love – is a red engorged raised rump, right under all our noses. But, one might object, the history of the Valentine symbol is complex, and although no one is quite sure of its origins, it seems quite implausible that it was coined with engorged female buttocks in mind. Indeed, engorged bums may have been the farthest things from the minds of the Valentine heart originator, but that does not mean that the Valentine heart might not nevertheless be about female rumps. Gobs of symbols were invented throughout history, and many may have been coined for symbolizing love. But only a tiny few have legs. Those that survive were culturally selected for, and their reason for surviving may have no relation to the reason they were originally conceived.

Valentine hearts may have been culturally selected for over time because of their similarity to engorged rumps.

In an earlier piece (http://www.scientificblogging.com/mark_changizi/topography_language) I discussed research of mine concerning how writing has come to be shaped “like nature” via cultural selection over time. Writing thereby taps into, or harnesses, the power of our visual system. Although not quite as life-changing as our ability to read, Valentine hearts tap into our visual system as well, looking like something quite natural, and eliciting passion in the viewer.

So next time you see someone drawing a Valentine, say “Shame on you!”

Mark Changizi is a professor of cognitive science at Rensselaer Polytechnic Institute, and the author of The Vision Revolution (Benbella Books). This first appeared on February 14, 2010, as a feature at ScientificBlogging.com.


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“But I thought you were blue!” That’s what Jake Sully, the main character in Avatar, says when he wakes up as an alien at the very end of the movie. Actually, the movie ends just before he has a chance to say anything, but that’s my guess about what he would have said. The question is: Why would he say that? (Or, if you’re a stickler: Why would I say he would say that?)

For those who haven’t seen the film, what you need to know is that Sully is a human who, from the safety of his brain-interface chamber back at the lab, can remotely control a “soul”-less alien body. And, at the end of the movie, and through the miracle of human suspension of disbelief, his human self gets literally uploaded into the alien’s body. Sully thereby becomes a bonafide eight foot tall, blue alien, and in the final frame of the movie we see his alien eyes open.

Question is: What does Sully see when he opens his eyes? And, more to the point: Does his new alien wife still appear blue to him?

By way of answering, let’s back up and remember what visual systems are for. When we look out at our world through our eyes, we implicitly believe we are seeing it as it truly is. Our eyes and visual systems are to us objective scientific measuring devices. But evolution does not select for objective scientific equipment – evolution selects for visual systems that best serve the animal and its reproduction. Although often the best perception is one that veridically reflects the truth, sometimes the best solution is a “useful fiction,” a little-white-lie perception that serves us better than an accurate accounting of the actual.

Consider the accent of your own voice. To you, you have no accent. It is other people that have an accent. And they think it is you that have an accent. Perceived accent, or “accentness”, is not a quality of the speech stream itself. Accentness is not an objective perception of anything out there. It depends on the baseline accent one has become adapted to, namely your own. When one adapts to a stimulus and it becomes baseline, the “qualitative feel” of that stimulus diminishes, i.e., it begins to feel like nothing to perceive it. The benefit of this is that even very  tiny deviations away from the baseline feel perceptually highly salient. Your own accent doesn’t sound accented because it is your baseline accent, allowing you to be trigger sensitive to the modulations around it from the voices of different people and their different emotional inflections. This is also why you don’t notice any smell to your own nose, any taste to your own tongue, or any temperature to your own skin.

And, in addition, it is why you don’t perceive your own skin to be colorey. People perceive the color of their own skin (or that of the most common one in their experience) as uncolorey and difficult to name. This perceptual adaptation to the baseline skin color allows people to be highly sensitive to the subtle color modulations happening on the skin of others as a function of mood or state.

Now we can circle back to our earlier question. When Sully opens his eyes as an alien, does his alien wife still appear blue to him? And the answer is no. He’s one of them now, and will perceive his wife’s skin, and his own skin, as peculiarly uncolorey, no longer blue at all. He will also not notice the taste of his own alien saliva, something you can be sure he would have noticed were he to have tasted alien saliva as a human. And now we see why alien Sully exlaimed, “But I thought you wereblue!” Let’s just hope he wasn’t into her only because she was blue!

Other pieces about color vision and skin are here, and also play prominently in my book, The Vision Revolution.

This first appeared on January 6, 2010, as a feature at the Telegraph.

Mark Changizi is a professor of cognitive science at Rensselaer Polytechnic Institute, and the author of The Vision Revolution (Benbella Books).

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A couple months back, one Heather Brundage got into the spirit of skin and color signaling, and rather than just jaw-jaw about it (my bag), she actually built clothes to do it. Check out these three posts, as she describes the stages of her idea, from conception to model showing off the dress.

http://www.heatherbrundage.com/Blog/2009/11/04/re-thinking-modesty/

http://www.heatherbrundage.com/Blog/2009/11/18/second-skin/

http://www.heatherbrundage.com/Blog/2009/11/19/second-skin-pictures/

Heather used temperature-sensitive materials. It doesn’t get at both dimensions our eyes can sense on the skin — concentration and oxygenation of blood in the skin — but it’s cool.

Another suggestion would be this: Have a person wear a dress matching his or her own skin tone, and then just cut out little square-sized holes in the dress! (Never a bad idea to have more reasons for removing more fabric from a dress.) This would best harness the oximetric capabilities of our eyes, optimizing our ability to see the emotions on the skin of the person. I talk about this idea in the context of hospital gowns here… https://changizi.wordpress.com/2010/02/01/why-patients-are-safer-in-nude/ , but what’s good for the hospital also may work for the single’s club.

Mark Changizi discusses his discovery that our color vision appears to have evolved for the purpose of seeing skin coloration in the first chapter of his book, The Vision Revolution. He is a professor in the Department of Cognitive Science at Rensselaer Polytechnic Institute.

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Other pieces of mine on skin and color vision:

Is Racism Due to Perceptual Illusions?

The Hue of Hefner

A Plea for More (Visible) Sex and Violence on TV (Or, Why Your Color Television Is Not Really in Color)

Santa’s Rosy Cheeks

Why Patients are Safer in Nude

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This first appeared on January 18, 2010, as a feature at ScientificBlogging.com.

If you ever have a mysterious skin rash and show your doctor, he or she may very well take a marker and encircle it, and then ask you to come back in a week. What’s the marker for? That’s obvious. If the rash is expanding, it may grow by only, say, 5% in a week, far too little to notice. But with the marker pen tightly encircling the original extent of the rash, any growth in the rash will become perceptually obvious because it will have grown beyond the boundary of the marker pen.

As obvious as this is for rashes, this basic principle is not currently followed for the much more acutely important skin color changes that occur in various medical conditions. Despite skin pallor having had a long history within medicine diagnosis, the medical community is currently handicapped in its ability to visually sense clinically relevant skin color modulations. For skin color, medicine is markerless. If a doctor sees a patient, and then sees the patient again later, the doctor will have little or no idea whether the skin has shifted. Quantitatively small color shifts can have tremendous medical implications: it can, for example, mean the difference between having healthy oxygen saturation and life-threateningly low oxygen saturation.

But we can do better. Our eyes have evolved, so I have argued in my research, to be near optimally sensitive to skin color changes due to underlying physiological changes in the blood. The skin color changes that mattered over evolution were socio-sexual signals, and socio-sexual signals tend to have strong spectral gradients our oximeter eyeballs are great at detecting. In fact, our eyes depend on these gradients to see skin colors. For example, our perception of blue-green veins depends crucially on its contrast with the surrounding skin. Blue-green veins if viewed all by themselves (i.e., through an aperture) do not appear blue-green at all. Veins are just slightly spectrally shifted toward blue-green compared to the skin’s baseline color, but when seen with the baseline color in the spatial surround, one sees the veins as genuinely blue-green.

Clinical color changes, on the other hand, are not selected to be seen – they are just side effects of being sick – and can often lead to much more spatially uniform shifts in color. And that’s the problem. If a patient’s skin color shifts a small amount for many clinical reasons (like central cyanosis), then when the doctor or nurse comes back, the color shift will often be imperceptible.

We can, however, fix this with a little marker pen. Rather than encircling the baseline extent of the rash, we need a marker pen to record the baseline color of the patient’s skin. And one place to begin marking up is the beloved hospital gown (although the same point will apply to any other colors visually proximal to the patient, such as the walls or sheets). The problem with hospital gowns is not just the drafty bum, but that gown colors are not designed to harness the oximetric, blood-diagnosing powers of our eyes.

The figure below shows four sample hospital gown colors, and on each of these colors I have placed the same five patches of skin. The central patch, let us presume, is your baseline skin color. The patches around the central patch are slightly color-shifted from the baseline, namely (from top, clockwise) bluer, redder, yellower and greener. Even with the baseline pitch there in the image, the color shifts are not perceptually salient. All the patches look qualitatively like the baseline patch’s color. And in real life the nurse or doctor would see the central patch, and then come back later and see just one of the shifted colors – determining if the color has changed would be nearly impossible.

mark changizi nude colored gown color changes

But now consider what happens if I lay those same five colored skin patches adjacent to a gown that has a color matching the baseline skin color in the center. In the figure below the four color-shifted patches look utterly and qualitatively distinct. They don’t look just a wee bit bluer, redder, yellower and greener than baseline. Rather, they now look distinctly blue, red, yellow and green. Again, these are the exact same four patches as were in each of the “gowns” in the previous figure.

mark changizi nude colored gown color changes

Here, then, is the simple prescriptive advice for hospitals: buy skin tone colored gowns, with colors relevant for the population you serve, and have patients wear a gown that best matches their baseline skin color. The tighter the color match, the more hypersensitive the eyes of the nurses and doctors are at sensing tiny spectral shifts away from baseline. I also suggest “skin color adhesive tabs” in a recent publication, which you can read here: http://www.changizi.com/colorclinical.pdf

Are these ideas relevant, you might ask, given that hospitals these days have cheap access to oximeters? Here is what co-author Kevin Rio and I write about this at the end of the article I just mentioned above:

One may wonder if these two techniques for harnessing color vision for oximetry are relevant in modern medicine, given the availability of pulse oximetry. [T]he clinical disciplines most utilizing pulse oximetry are also the disciplines that most often refer to the patient’s clinical skin color in diagnosis: thus, the actual practice of medicine appears to value our human color capabilities, despite the presence of pulse oximetry. There are several potential explanations for this: (a) color perception provides redundant detection of oxygen saturation (e.g., if the oximeter becomes unattached), (b) observation of skin color modulations may lead to a faster behavioral response by the clinician (the “look” of sickness may be more psychologically engaging than numbers or beeps from an oximeter), and (c) our color perception is capable of sensing the spatial gradients in skin color across the body, and the nature of those gradients can impart information to a clinician. Furthermore, there are circumstances where pulse oximetry is not used today, but where the “color oximetry” techniques above would be of great value: (i) in certain parts of the hospital (e.g., in transit, or the emergency department waiting room), (ii) in third world hospitals, where it is still not part of standard care, (iii) in the field (e.g., for athletes or soldiers, and (iv) in the home (e.g., for SIDS detection).

Haiti comes to mind.

Mark Changizi is a professor of cognitive science at Rensselaer Polytechnic Institute, and the author of The Vision Revolution (Benbella Books).


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Have you ever noticed that Santa’s rosy cheeks are visible despite his furry face? It is as if his facial hair “purposely” keeps out of the way of his color signals. I have argued in my research that some of us primates evolved bare faces (and rumps) in order to color signal. In fact, our color vision appears to be optimized for sensing these blood-modulated color signals. I talk about this in detail in Chapter 1 of The Vision Revolution, and you can also find a variety of pieces related to this on my ChangiziBlog.

Santa's rosy cheeks are not obscured by his beard.

In this light, here is an excerpt from a piece Roger Highfield wrote about Santa’s beard before he became editor of New Scientist.

Research by Dr Mark Changizi of America’s Rensselaer Polytechnic Institute has suggested that we may have evolved our particular brand of colour vision to discriminate between slight changes in skin tone due to blushing, rage and blanching.

A survey of our primate relatives suggests that this kind of vision is only found in those with bare faces, such as humans, and is tuned precisely to detect changes in skin tone.

But even a beard as luxuriant as Santa’s should not hinder his ability to send out a colour signal, such as a healthy glow. After all, says Dr Changizi, we could have evolved to sprout hair anywhere – for example, on the cheeks, forehead and nose, which are the first areas to go red.

“But facial hair doesn’t end up there,” he points out. “You can really appreciate what beards don’t do by looking at men with the condition of hypertrichosis, when their faces are covered with hair.

“In terms of Father Christmas, note how the songs mention his rosy cheeks. Even Santa can colour-signal, despite his facial hair, because evolution has made sure that his beard and moustache got out of the way.”

See the entire piece here.  Roger Highfield has a book about the science of Christmas, in fact: Can Reindeer Fly?: The Science of Christmas (Orion).

Merry Christmas!

Mark Changizi is a professor of cognitive science at Rensselaer Polytechnic Institute, and the author of The Vision Revolution (Benbella Books).

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This first appeared on December 7, 2009, as a feature at ScientificBlogging.com.

Dear TV and Movie Producer Person,

I realize that you receive letters all the time complaining about the gratuitous sex and violence on television and in movies. This is not one of those letters. In a sense, I want more sex and violence. Let me explain.

It is worth reminding ourselves why we watch TV and movies. First and foremost, we watch to be entertained. And, secondly, we watch because we get to watch. That is, we watch TV and movies because the visual modality of the experience brings an evocativeness of its own, one that we seem to like. Sure, we like the dialog and the plot twists, but we could have dialog and plot twists via reading or listening to books. We watch TV and movies because, in addition, we get that visual evocativeness.

And one of the best ways to be visually evocative is to show us the characters in the story expressing their emotions. There are a variety of ways to see the emotions in the characters, and gestures and facial expressions are two of the most obvious. But a third avenue for visually communicating the emotions of the characters is the color of the skin, whether on the face or other bare spots. These color signals are especially primal and evocative, and although one is not always consciously aware of sensing these color signals, our color vision is highly optimized for sensing the blood modulations in the skin underlying the color changes.

I want to see these color signals on TV and in movies. I want to see the anger spread over the bad guy’s face when his bomb is found and disarmed. I want to see the subtle blush on the female lead when she’s engaged in frothy banter. I want to see the ashen face of the zombie. And I want to see the veins in the neck of the victim just before the vampire chomps.

But here is the problem, TV and movie producer person: You don’t show us these visually evocative color signals on the skin of your characters. I want movies that don’t merely show skin, but show the emotion on the shown skin. Without this, your shows and movies are emotionally flat, and could be severely enriched.

But instead of aiming to raise the emotionality of our viewing experience to the emotional-3D, you bring us more pixels. Is the greater resolution of HD-TV giving us a truly more evocative experience? The visual detail is indeed impressive, and the educational and sports uses of TV probably benefit from this. But for what I take to be the mainstay of TV and movies – the stories, with actors – I doubt HD-TV makes any difference. In fact, I tend to wear contact lenses that are several years behind the actual needs of my ever-declining eyes. I can hardly read the volume-readout on the screen of my television, much less see the two-million-pixel detail in my expensive HD-TV. But, believe me, I get plenty of evocativeness from the bodies of the humans around me in my life. (Mostly, alas, just my kids’ emotions.) Color signals on bodies, you see, are not in HD.

What we really want is skin-TV, not HD-TV.

TV and movies do give us skin-TV, but only in cartoons. For example, Disney cartoons have long used color modulations on the faces of their characters to bring the emotion to life. Nevermind that many of these characters are furry-faced mammals, or are sponges that don’t even have blood. Cartoonists know how to be evocative, and liberally color signal. Yet you TV and movie people won’t give us this level of evocativeness when real people are on the screen.

There’s a reason you won’t give us skin-TV. It’s that you can’t. Television and movie projection can show these color signals, which is why Spongebob can be seen to blush. The problem is that the cameras used in TV and movies cannot pick up these skin color signals. Cameras have color filters that are very different from the sensitivities of the cones in our eyes. Whereas our cone sensitivities are optimized for sensing the underlying physiological modulations of blood in the skin (they are, in essence, oximeters), cameras are designed to be general-purpose three-filter spectrometers, and can’t detect these skin color changes.

The color dimension that we primates have, but other mammals do not, is the red-green one, and this color dimension is optimized for sensing modulations of oxygenation of the hemoglobin in the skin. Red-green modulations are about the emotions associated with these modulations in oxygenation. The color cameras are able to record modulations in red and green, of course, but not in the one place where it appears to matter most for the evolution of this color sense: on skin. Color television and movies are, in a sense, then, not in color at all. The red-green modulations are found in all the non-skin places, but not on the skin where our eyes evolved to see it. That’s what would have to be fixed in order to raise the level of evocativeness of TV and movies to the emotional-3D.

But designing cameras to let us see skin on screen as our eyes see it in person turns out to be a difficult engineering problem, and I have no insights on how to solve it. My aim with this open letter is to provide new motivation for trying harder to solve it. Lacking the appropriate technology does not merely result in perceptions of the screen that differ from what it would look like in person. Rather, it results in a difference where it matters most: on the skin, and the resulting signaled emotion. If camera technology is not the route to solving this problem, then the other route is to use advances in CGI to add color signals to the bare skin of the characters. …to bring more sex and violence to television and movies, Disney style.

Mark Changizi is a professor of cognitive science at Rensselaer Polytechnic Institute, and the author of The Vision Revolution (Benbella Books).

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Today I was on LateNightLive (of ABC Radio National) with host Phillip Adam.  In addition to divulging my enjoyment at running over pigeons, I got a chance to talk about sex, blood, the blind, writing, rabbit-heads and other topics from The Vision Revolution.

Late Night Live

Late Night Live

Check out the segment here. (Download the mp3.)

Mark Changizi is a professor of cognitive science at Rensselaer Polytechnic Institute, and the author of The Vision Revolution (Benbella Books).

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