What You See Ain't What's Out There


Learning to see. Sounds like a crazy phrase, right? Aren’t animals (including humans) born knowing how to see? And how could we ever know what is the case, since babies can’t communicate?

Well, there are ways of finding answers without going down the Nazi medical experiments road, writes David Eagleman in his terrific book, Incognito: The Secret Lives of the Brain. Like the case of Mike May, whose eyesight was restored at the age of 43. When the bandages were removed post-surgery:
“He stared with utter puzzlement at the objects in front of him. His brain didn’t know what to make of the barrage of inputs… He was experiencing only uninterpretable sensations of edges and colors and lights. Although his eyes were functioning, he didn’t have vision.”
Hmmm, but you’re not convinced yet. Eagleman continues:
“Mike knew from a lifetime of moving down corridors that walls remain parallel, at arm’s length, the whole way down. So when his vision was restored, the concept of converging perspective lines was beyond his capacity to understand. It made no sense to his brain.”
And so Eagleman concludes:
“Vision does not simply exist when a person confronts the world with clear eyes. Instead, an interpretation of the electrochemical signals streaming along the optic nerves has to be trained up.”

Still not convinced? Then think of holograms:
“(Try taking) two photographs from a few inches apart, and then putting them side by side. Now cross your eyes so that the two photos merge into a third, and a picture will emerge in depth… The impossible notion of depth arising from a flat image divulges the mechanical, automatic nature of the computations in the visual system.”

But wait, things get even more weird. Take this pic of the cube on the left, an example of “multistable” stimulus:

As Eagleman explains:
“Staring at the picture for a moment, you’ll notice the front face appears to become the back face, and the orientation of the cube changes… nothing has changed on the page, so the change has to be taking place in your brain. Vision is active, not passive.”

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