Tuesday, March 04, 2008

Do babies see different colors than adults? Who knows?

World of Color
Originally uploaded by n!ck.
Note: Let me say right up front that this post got a little out of hand. I think there's good stuff below, but read on duly warned.

Okay. Here goes.

I came across an interesting article today on the differences between color perception in babies and in adults. I first saw a discussion of the findings on Wired's Science Blog, with the provocative title, "Babies See Pure Color, but Adults Peer Through Prism of Language." The Wired author, Brandon Keim, writes:
When infant eyes absorb a world of virgin visions, colors are processed purely, in a pre-linguistic parts of the brain. As adults, colors are processed in the brain's language centers, refracted by the concepts we have for them.
And then a little later:
Over the course of our lives, it appears that an unfiltered perception of color gives way to one mediated by the constructs of language.
Well that's an interesting claim. Wonder if there's anything to it. Before too many thoughts fired off, though, I saw that Keim undoes his own title right at the end:
Does this mean that adults and infants see the same colors differently?

"We don't know," said study co-author Paul Kay.
So babies don't see pure colors (whatever those are)? That's too bad.

Write ups of scientific journal articles often play up some minor implication of the research, which makes sense since most journalists don't have a serious scientific background and they're writing for general audiences. So when I have anything like a passing familiarity with the issue, I look up the original article. (Luckily, they tend to be short.) The one Keim discusses is a 2008 piece in PNAS (Proceedings of the National Academy of Sciences) by Franklin et al. with the markedly less sexy title, "Categorical Perception of Color Is Lateralized to the Right Hemisphere in Infants, but to the Left Hemisphere in Adults." The upshot is that adults categorize colors faster when they're presented only to their right visual fields. (Your right visual field basically contains only what comes in through your right eye.) Infants (4- to 6-month-olds for this study), reacted faster when the colors were presented only in their left visual fields. There you go.

Sounds possibly cool, but so what? Well, stuff seen the right visual field gets fed to the left hemisphere of the brain, and the left visual field stuff goes to the right hemisphere. (The brain and body are wired contralaterally, as they say in the biz.) The left hemisphere is also happens to be where language processing occurs. So, it seems that adults rely on language to categorize colors whereas infants don't. Or to put it in fancy science talk:
However, the absence of a category effect in the [left hemisphere] for infants, but the presence of a greater [left hemisphere] than [right hemisphere] category effect for adults, suggests that language-driven [categorical perception] in adults may not build on prelinguistic [categorial perception] but that language instead imposes its categories on a [left hemisphere] that is not categorically prepartitioned.
That means that adults see colors differently than infants. Right?

This is why we actually need philosophers to sort out what people mean when they say things. Basically the authors are claiming that learning color words creates color categories that aren't innate. But why think that the categorizations are different? Do the infants sort colors themselves differently (some red as blue, say) and not simply use a different part of the brain to track the same color properties out in the world? Language mainly lets us talk about things when they're not around and in more detail; why conclude that language always changes what is already there? As I mentioned a while back, some believe that language doesn't "get in between" (add something new to) an experience and its expression, but instead replaces the expression.

More importantly, why think that differences in where information gets processed in the brain translate into different conscious experiences — that is, that babies see pure colors while adults' color experiences are "refracted" through language simply because language happens on the left side of our heads. And how would you tell if babies (consciously) saw colors As They Really Are? After all, humans are trichromats and have eyes sensitive to only certain wavelengths of light unlike, say, some birds that are tetrachromats. Which means it's pretty tough, if not in principle impossible, to know what a pure color — meaning, presumably, a color apart from any perceiver — would be. Add to that all sorts of research showing that humans can track all sorts of things nonconsciously, which means that evidence about tracking bias reveals little about the nature of conscious tracking experience — or what it's like for one to see colors. (The phenomenon called "blindsight" is an incontrovertibly cool example of nonconscious tracking.)

Whew. Okay. So all I really wanted to point out was that both the Wired guy and the PNAS folks don't really have a clear idea what they're talking about because they haven't cleanly drawn their own categories — conscious v. nonconscious seeing, seeing v. not seeing v. experiencing, color properties v. color experience, and so on.

And but so what colors do babies see? Who knows? These guys don't.

1 comment:

Nadine said...

I loved this post, since I'm constantly wondering what our little girl sees (and what she thinks of what she sees).

So colorblindness is like a language gap?