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

214 J HOW THE MIND WORKSverbal mind. That mental symbol, and the mental propositions that capturethe spatial relations among objects ("book lying face down ion shelfnear door"), are examples of the "description" that Marr charged visionwith computing.If vision did not deliver a description, every mental faculty—language,walking, grasping, planning, imagining—would need its own procedurefor deducing that the trapezoid on the retina is a rectangle in theworld. That alternative predicts that a person who can call a slanted rectanglea "rectangle" may still have to learn how to hold it as a rectangle,how to predict that it will fit into rectangular spaces, and so on. Thatseems unlikely. When vision deduces the shape of an object that gaverise to a pattern on the retina, all parts of the mind can exploit the discovery.Though some parts of the visual system siphon off information tomotor-control circuits that need to react quickly to moving targets, thesystem as a whole is not dedicated to any one kind of behavior. It createsa description or representation of the world, couched in objects and 3-Dcoordinates rather than retinal images, and inscribes it on a blackboardreadable by all the mental modules.This chapter explores how vision turns retinal depictions into mentaldescriptions. We will work our way up from splashes of light to conceptsof objects, and beyond them to a kind of interaction between seeing andthinking known as mental imagery. The repercussions reach to the rest ofthe psyche. We are primates—highly visual creatures—with minds thatevolved around this remarkable sense.DEEP EYELet's begin with the stereograms. How do they work, and why, for somepeople, don't they work? Despite all the posters, books, and jigsaw puzzles,I have not seen a single attempt at explaining them to the millionsof curious consumers. Understanding stereograms is not only a good wayto grasp the workings of perception but it is also a treat for the intellect.Stereograms are yet another example of the marvelous contrivances ofnatural selection, this one inside our own heads.Autostereograms exploit not one but four discoveries on how to trickthe eye. The first, strange to say, is the picture. We are so jaded; by photographs,drawings, television, and movies that we forget that they are a