Monthly Archives: May 2010

Everything We Knew About Human Vision is Wrong: Author Mark Changizi Tells Us Why

For theoretical neurobiologist and author Mark Changizi, “why” has always been more interesting than “how.” While many scientists focus on the mechanics of how we do what we do, his research aims to grasp the ultimate foundations underlying why we think, feel and see as we do.  Guided by this philosophy, he has made important discoveries on why we see in color, why we see illusions, why we have forward-facing eyes, why letters are shaped as they are, why the brain is organized as it is, why animals have as many limbs and fingers as they do, and why the dictionary is organized as it is.

His latest book, The Vision Revolution, is a trenchant and insightful investigation into why humans see and interact with the world as we do. His findings are challenging and often surprising, and his witty, engaging style is accessible to a broad range of readers . He was generous enough to spend a few minutes with me recently to discuss his book and other topics.

NN: What originally led you to write a book about human vision in particular, instead of any of the other human evolutionary adaptive traits?

MC: Indeed, I don’t consider myself solely a vision scientist. I call myself a theoretical neurobiologist, more generally, and I have had a number of non-vision research directions, including, for example, the shape and evolution of the brain, and why animals have as many limbs and digits as they do.  Some of these research directions were central parts of my first book, The Brain from 25,000 Feet.

I was led to a book on vision because that’s where my research led me, and so the question is, Why did I end up with quite a few research directions in vision?

As a theoretical neurobiologist, I try to find interesting phenomena that I can wrap my head around, with the hope of putting forth and testing rigorous and general explanatory hypotheses. That’s not easy, but there are a number of reasons why it’s easier for vision.

First, relative to other senses and/or behaviors, the amount of data we possess for vision is huge. There’s a century-sized pile of data, much of it not well explained, much less in a unifying manner.

Second, vision is theoretically approachable. You have a visual field, you see objects, and so on. We know how to at least begin thinking about the phenomenology. It’s more difficult for audition, and practically impossible for olfaction, where we have little idea how to even describe our perceptions. …forget about explaining anything!

And, third, for vision we have the best understanding of the underlying mechanisms.

My point is that, as a theorist struggles for phenomena he or she can crack, vision appears as a large attractive target compared with many other aspects of brain and behavior. One may end up attacking vision problems even if one isn’t excited by vision, merely because it’s juicy. (I am excited by it, though, especially to the extent that I can find exciting hypotheses.)

I was intrigued by the “mind reading” aspects of vision.  In a nutshell, how does this work, and how do humans benefit from this ability?

Our color vision fundamentally relies upon the cones in our retina, and I argue in my research that color vision evolved in us primates for the purpose of sensing the emotions and states of those around us. We primates have an unusual kind of color vision – our cones sample the visible spectrum in a peculiar fashion – and I have shown that one needs that kind of peculiar color sense in order to pick up the color modulations that occur on our skin when we blush, blanch, redden with anger, and so on. Our funny primate variety of color vision turns out to be optimized for seeing the physiological modulations in the blood in the skin that underlies our primate color signals.

So, we evolved special mechanisms designed for sensing the emotions and states of others around us. That sounds a lot like the evolution of a “mind-reading” mechanism, which is why I (only half in jest) describe it that way.

You mention in the book that reading and writing are relatively recent advances in human development, and yet we take for granted that we “see” and understand words, as if our brains were simply meant to see and understand them.  What’s really going on that allows us to make sense of symbols on a page—and why can we do this at all?

In talks I often show a drawing of a child reading a book titled “How to Somersault.” The “joke” is that most kids are able to read very early, often even before they can do stereotypical ape behaviors like somersaults and monkey bars. Sure, they comprehend speech much earlier, but they’re getting orders of magnitude more speech thrown at them than writing. Kids learn to read very early, and very well; and as adults we are ridiculously capable readers, and spend nearly all our day reading.

Aliens might be excused for thinking we evolved to read.

But the invention of writing is only thousands of years old. In addition, for most of us, our grandparents, great grandparents or great great grandparents didn’t read at all. Writing is much too recent for our brains to have evolved to have reading mechanisms.

How does our brain do it?

Is it because our visual system can become good at reading whatever we present to it? No. Kids would surely not be capable readers by around six if they were tasked to read bar codes or fractal patterns.

The solution is that culture made writing easy on the eye, by shaping letters to be what the eye likes. The idea that culture shapes our artifacts to be good for us is not new. What’s new here is a specific hypothesis for what writing should look like in order to be good for us.

To be easy on the eye, writing needs to “look like nature,” just what our illiterate visual systems are fantastically competent at processing. The trick of that research direction was making this “writing looks like nature” idea rigorous, and coming up with ways of testing it. I show that there are certain signature visual patterns found in nearly any natural environment with opaque objects strewn about, and that these signature patterns are found in human writing. In short, writing has evolved so that written words look like visual objects.

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