Steven Pinker -- How the Mind Works - Hampshire High Italian ...

The Mind's Eye | 213When the current world resembles the average ancestral environment,we see the world as it is. When we land in an exotic world where theassumptions are violated—because of a chain of unlucky coincidences orbecause a sneaky psychologist concocted the world to violate theassumptions—we fall prey to an illusion. That is why psychologists areobsessed with illusions. They unmask the assumptions that naturalselection installed to allow us to solve unsolvable problems and know,much of the time, what is out there.Perception is the only branch of psychology that has been consistentlyadaptation-minded, seeing its task as reverse-engineering. Thevisual system is not there to entertain us with pretty patterns and colors;it is contrived to deliver a sense of the true forms and materials in theworld. The selective advantage is obvious: animals that know where thefood, the predators, and the cliffs are can put the food in their stomachs,keep themselves out of the stomachs of others, and stay on the right sideof the cliff top.The grandest vision of vision has come from the late artificial intelligenceresearcher David Marr. Marr was the first to describe vision assolving ill-posed problems by adding assumptions about the world, andwas a forceful defender of the computational theory of mind. He alsooffered the clearest statement of what vision is for. Vision, he said, "is aprocess that produces from images of the external world a descriptionthat is useful to the viewer and not cluttered with irrelevant information."It may seem strange to read that the goal of vision is a "description."After all, we don't walk around muttering a play-by-play narration ofeverything we see. But Marr was referring not to a publicly spokendescription in English but to an internal, abstract one in mentalese.What does it mean to see the world? We can describe it in words, ofcourse, but we can also negotiate it, manipulate it physically and mentally,or file it away in memory for future reference. All these featsdepend on construing the world as real things and stuff, not as the psychedeliaof the retinal image. We call a book "rectangular," not "trapezoidal,"though it projects a trapezoid on the retina. We mold our fingersinto a rectangular (not trapezoidal) posture as we reach for it. We buildrectangular (not trapezoidal) shelves to hold it, and we deduce that it cansupport a broken couch by fitting into the rectangular space beneath it.Somewhere in the mind there must be a mental symbol for "rectangle,"delivered by vision but available at once to the rest of the verbal and non-