Thursday, July 10, 2008

The Mask of Perception

We are told that "seeing is believing," but how good a witness is our perception, really?

Neurologists call the understanding of perception that most people have “the naïve view.” We’re inclined to think we normally perceive things in the world directly. We believe that the hardness of a rock, the coldness of an ice cube, the appearance of a face, and so on are picked up by our nerve endings, transmitted through the spinal cord like a message through a wire, and decoded by the brain. The naïve view assumes that the sensory data we receive from our eyes, ears, nose, fingers, and so on contain all the information that we need for perception. Yet, as scientists set about analyzing the signals, they found the sensory data to be radically impoverished.

The perceptions of our mind are extraordinarily rich. We can tell if something is liquid or solid, heavy or light, dead or alive. But the information we work from is poor - a distorted, two-dimensional transmission with entire spots missing. So the mind fills in most of the picture. Watching a dog as it runs behind a fence, our eyes receive only separated vertical images of the dog, with large slices missing. Yet somehow we perceive the dog to be whole, an intact entity travelling through space. The eyes receive slices of the picture, the mind fills in the gaps. Visual sensation augmented by mental perception.

The more we examine the actual nerve transmissions we receive from the world outside, the more inadequate they seem. You can get a sense of this from brain-anatomy studies. Writing in The New Yorker, Atul Guwande, an associate professor at Harvard Medical School, notes that if visual perceptions were primarily received from the eyes rather than constructed by the brain, you'd expect that most of the fibres going to the brain's primary visual cortex would come from the retina. Instead, scientists have found that only 20 percent do; 80 percent come downward from regions of the brain governing functions like memory. Richard Gregory, a prominent British neuropsychologist, estimates that visual perception is more than 90 percent memory and less than 10 percent sensory nerve signals.

Author Richard Dawkins reminds us that the human brain runs some first-class simulation software. Our eyes do not present a faithful photograph to our brains of what is out there, like some accurate movie of what is going on through time. Instead, our brains construct a continuously updated model: updated by coded pulses chattering along the optic nerves, but constructed nevertheless. Constructing models is something at which the human mind is very good.

This simulation software in the brain is particularly adept at constructing faces and voices. For evidence, consider this amazing video clip, or this one, or this. And so on. Seriously, check these out - they're really worth the minimal effort of clicking over.

These clips aren't trick photography and there is no trick in the construction of the masks. The trickery is all in your mind. The brain's simulation software receives data indicating the presence of a face, perhaps nothing more than a pair of eyes, a nose and a mouth in approximately the right places. Having received these sketchy clues, the brain does the rest. The face simulation software kicks into action and it constructs a fully solid model of a face, even though the reality presented to the eyes is a hollow mask.

All this is illustrative of the formidable power of the brain's simulation software. With just a little bit of data (10 percent visual sensation), the mind constructs what it is conditioned to perceive (90 percent perception). We live in a matrix of our own device.

In a 1710 “Treatise Concerning the Principles of Human Knowledge,” the Irish philosopher George Berkeley maintained that we do not know the world of objects, we know only our mental ideas of objects. “Light and colours, heat and cold, extension and figures - in a word, the things we see and feel - what are they but so many sensations, notions, ideas?” Indeed, he concluded, the objects of the world are likely just inventions of the mind. Berkeley recognized serious flaws in the direct-perception theory - in the notion that when we see, hear, or feel we are just taking in the sights, sounds, and textures of the world. For one thing, it cannot explain how we experience things that seem physically real but aren’t: dreams that can seem indistinguishable from reality; feelings of itchiness that arise from merely thinking about ants on our skin; rotating faces on the hollow sides of masks.

The mind stores the templates for our perception in its memory, and is conditioned to first apply those templates which suggests a threat. Thus, we are more inclined to mistake a shadow for a burglar than a burglar for a shadow. A false positive might be a waste of time - a false negative might be fatal. Secondly, we apply those templates that we find pleasurable. All of those templates in between for neutral perceptions - that which are neither threatening nor pleasurable - are generally ignored. Thus, if we really want to know the world around us, we must first know our own minds.

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