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The Body Has a Mind of Its Own

Think of a still lakeside inlet fringed with rushes and dotted with lily pads. Consider how this scene looks very different to different kinds of animal -- say, a fron, a hippo and a sparrow. Each takes in the scene instantly as an array of affordances. Both the frog and the hippo see it as something they can swim through and sumberge themselves in; but the affordances of swimmability and submersibility do not even occur to the sparrow. The frog and the sparrow see the lily pads as potential platforms - that is, as things that afford sitting; the hippo sees them only in terms of their swallowability, with sittability not entering its mind for a nanosecond.

You also perceive the world through an automatic filter of affordances. Your perception of a scene is not just the sum of its geometry, spatial relations, light, shadow, and color. Perception streams not just through your eyes, ears, nose and skin, but is automatically processed through your body mandala to render your perceptions in terms of their affordances. This is generaly true of primates, whose body mandalas have grown so rich with hand and arm and fine manipulation mapping, and even more so for you, a human animal.

Consider a blue jay perched on your windowsill, looking in at your workspace. In one sense you and the bird see the identical scene. The bird has extremely keen vision, probably even keener than yours. But despite this, in a crucial sense, the bird doesn't see the same chair or coffee mug or keyboard that you see, and the reason comes down to affordances. We tend to think of visual understanding of an object to be all about edges, angles, textures, colors, shadows, and so forth. That's the basic part of vision; but there's a lot more that goes on in your brain after those low-level features are analyzed. As visual information makes its way up the cortical visual hierarchy, more abstract or complex features are inferred from it, such as detecting motion, identifying body parts or faces and knowing what objects belong where. At even higher stages, it gets handled by multisensory areas including , crucially, the body maps of the posterior parietal and frontal motor cortex. We are less directly aware of this higher visual processing, but it is extremely important. When you see a chair, you "see" its sittability, its stand-upon-to-reach-the-high-shelf-ability, and other uses that your human body can make of it and when you see a coffee cup, you see its graspability, its volumetric capacity, its drink-holding-ness. These are body- and action-based concepts, but they are automatically evoked by the sight of the chair and coffee cup. The blue jay, meanwhile, does not see any of these affordances, though it may see different ones. It may see the coffee cup as affording head-insertability, where it could conceivably find something worth eating. It certainly sees the top of your chair's backrest as an affordance for perching, which isn't something that occurs naturally to you.

A region of your premotor cortex has several indispensable functions. One of them is transforming visual and semantic information (knowledge based on something's meaning or general use) about an object directly into a motor command that shapes your hand appropriately. For example, as you reach for a coffee cup, your hand picots to vertical and your fingers hook just right so that you can pick it up in a way that affords drinking. When you reach for a fork, your hand assumes a different shape en route to making contact with it, so that you end up with a perfect grip for scooping pasta into your mouth. In short, some of the neural circuitry in your frontal lobe, along with a similar region in the parietal lobe, contributes to your ability to perceive and use tools correctly. Graspability, pushability, typability, pokeability, steppability, climbability, cursor controllability -- all kinds of usability are perceived automatically at a preconscious level through these higher-order body and space maps.

The Body Has a Mind of Its Own

How Body Maps in Your Brain Help You Do (Almost) Everything Better

By Sandra Blakeslee and Matthew Blakeslee

p.106-7

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