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The whole dress that melted the internet thing has brought back a curious example of semi-demi-science about a Namibian tribe that can't distinguish green and blue, but does differentiate kinds of green that look just the same to us Westerners. This story has been floating around the internets for several years, in places like the BBC and the New York Times and BoingBoing and RadioLab, and it presents an impressive-seeming demonstration of the power of language to shape our perception of the world. But on closer inspection, the evidence seems to melt away, and the impressive experience seems to be wildly over-interpreted or even completely invented.

I caught the resurrection of this idea in Kevin Loria's article "No one could see the color blue until modern times", Business Insider 2/27/2015, which references a RadioLab episode on Colors that featured those remarkable Namibians. Loria uses them to focus on that always-popular question "do you really see something if you don't have a word for it?"

[Update — apparently the experiment under discussion never actually existed, but was concocted for illustrative purposes by the authors of a BBC documentary: see "Himba color perception", 3/17/2015. And that's why the stimuli don't make seem to correspond to the claims made about them — they're essentially fraudulent.]

Here's the relevant segment of Loria's piece:

A researcher named Jules Davidoff traveled to Namibia to investigate this, where he conducted an experiment with the Himba tribe, which speaks a language that has no word for blue or distinction between blue and green.

When shown a circle with 11 green squares and one blue, they could not pick out which one was different from the others — or those who could see a difference took much longer and made more mistakes than would make sense to us, who can clearly spot the blue square.

But the Himba have more words for types of green than we do in English. When looking at a circle of green squares with only one slightly different shade, they could immediately spot the different one.

Can you?

For most of us, that's harder.

No kidding.

Davidoff says that without a word for a color, without a way of identifying it as different, it is much harder for us to notice what is unique about it — even though our eyes are physically seeing the blocks it in the same way.

The images in Loria's article are apparently screenshots from a segment of a 2011 BBC documentary "Do you see what I see?". The relevant segment is available via Vidipedia and BoreMe, and the section about the Himba of Namibia starts about 3:00 of the BoreMe version.

The striking story about the Himba's color perception has been widely disseminated — aside from the RadioLab episode, there's Mark Frauenfelder, "How language affects color perception", BoingBoing 8/12/2011; Maud Newton, "It's not easy seeing green", NYT 9/4/2012; and Dustin Stevenson, "The last color term", 4/25/2013; and so on.

Most of the articles have the same pair of examples that Loria shows — a circle of 12 green squares, one of which is a slightly different green from the others, and similar circle with 11 green squares and one blue square. Unfortunately, like Loria, most of the others show the blue-and-green display only as a photo of a CRT display taken over the shoulder of a Himba subject doing the task.

Mark Frauenfelder at BoingBoing was interested enough to use an image-processing program to calculate the RGB values of the squares in the varieties-of-green display:

I get slightly different values from Loria's image: [85 168 0] for the oddball green square, and [72 166 8] for various of the other green squares. (I loaded the image into Gimp via "Copy Image" and "Create>>From Clipboard", and used the eyedropper tool to measure RGB values. In fact the values vary slightly for different parts of different squares.) For the "white" background (which is necessary for turning RGB values into CIELUV values) I get [242 242 242]. Frauenfelder doesn't specific the value of the "white" background in his image, but I get [244 244 246] from it.

From the stimulus seen over the shoulder of the Himba subject, I get [23 88 110] for the blue-looking square, and [27 74 54] (plus or minus a bit) for the green-looking ones, with "white" at [97 108 102]. This is very unsatisfactory — but it's what they give us.

So I implemented the algorithms to convert from RGB to CIEXYZ and then to CIELUV (given e.g. here), because euclidean distance in L*u*v* space is said to be roughly equal to psychophysical distance. My implementation is here.

The result for the kinds-of-green display, using my measurements:

green1a = [85 168 0];

green1b = [72 166 8];

white1 = [242 242 242];

norm(rgb2luv(green1a, white1) - rgb2luv(green1b, white1))

ans = 8.4526

And using Frauenfelder's measurements:

green1a = [97 192 4];

green1b = [80 186 15];

white1 = [244 244 246];

norm(rgb2luv(green1a, white1) - rgb2luv(green1b, white1))

ans = 10.606

And from the over-the-shoulder shot (as found in Loria's screenshot):

blue2 = [23 88 110];

green2 = [27 74 54];

white2 = [97 108 102];

norm(rgb2luv(blue2,white2) - rgb2luv(green2,white2))

ans = 46.446

So maybe the CIELUV space is highly ethnocentric. Or maybe the documentary's assertion about the perception of these stimuli is just wrong — the blue and the green are 4-6 times farther apart, in psychophysical terms, than the different kinds of green are.

Or maybe the over-the-shoulder shot somehow exaggerates the amount of blue-green contrast (though I would expect the opposite). So I went looking for a better version of the blue-vs.-green stimulus. One of the pages that I cited (Dustin Stevenson, "The last color term", 4/25/2013) gives a more comparable-looking blue-vs.-green display (i.e. not an over-the-shoulder photo):

The RGB values from this image, with the associated CIELUV distance, are:

blue2 = [0 0 255];

green2 = [58 185 5];

white2 = [242 242 244];

norm(rgb2luv(blue2,white2) - rgb2luv(green2,white2))

ans = 234.54;

But the blue value of [0 0 255] in this display is obviously either an innocent but wildly mistaken invention by Mr. Davidson, or else a complete fraud — this version is even less satisfactory than the over-the-shoulder image. It suggests that the blue-green difference is 20-30 times more salient, in purely psychophysical terms, than the green-green difference is.

So I went looking for a publication with a clear description of the stimuli, as well as a description of the experiment and the results. And I struck out, utterly and completely.

Looking for Himba color in Google Scholar, I find things like Rachel Adelson, "Hues and views: A cross-cultural study reveals how language shapes color perception", American Psychological Association Monitor, 2/2005; Roberson et al., "Color categories: Evidence for the cultural relativity hypothesis", Cognitive Psychology 2005; Goldstein et al., "Knowing color terms enhances recognition: Further evidence from English and Himba", Journal of Experimental Child Psychology 2008 — but none of these describe an experiment anything like the one shown in the 2011 BBC documentary, and discussed in various places since then.

The documentary names Serge Caparos as the experimenter, and we see him and hear him running the experiment and discussing the results. But as far as I can tell, searching for Serge Caparos Himba color again leaves us without any publication that describes the experiment we're looking for.

So either

The experiment was abandoned because it failed, or because serious design flaws turned up in the review process; or The experiment was abandoned because the author(s) went on to other things, or couldn't write it up for personal reasons; or The experiment has been published, but my search techniques were unable to find it.

Whatever the explanation, I submit that the BBC documentary (and the subsequent coverage) has given us a sensationalist interpretation of an undocumented experiment, presented as reliable science, without giving us any basis to trust that this interpretation is even close to true.

Unfortunately, this is all too typical of the BBC's approach to the popularization of science — see "It's always silly season in the (BBC) science section" for a inventory of examples as of a decade ago, and "Bible Science stories" for a theory about the source of this pathology.

It would be funny if it weren't so sad, or maybe vice versa.

If you'd like to learn more about color vision (at least in the whole-field case), and you know a little linear algebra and/or have access to Matlab or Octave, you may be interested in some Lecture Notes on the subject of early color vision, and perhaps even in this homework assignment.

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