J. Bradford DeLong
delong@econ.berkeley.edu
http://www.j-bradford-delong.net/

July 2001


When I was fifteen I played in a football game on Mt. St. Albans, the highest point in Washington, D.C. It began to thunder and rain. We huddled under the eaves of the St. Albans School and looked back across the field. There was a blinding, dazzling flash as a lightning bolt struck a tree some 500 feet away. Then for two-thirds of a second there was total silence, save for the soft sound of the rain. Only then did the crack of the thunderstroke shake us, and the rolling echoes of the thunder wash over us.

This morning I bent down to touch my toes. I watched as my outstretched fingers made contact, and at that very instant I felt the pressure of my toes on my fingers, of my fingers on my toes. But I have been told that the speed of nerve signal transmission is limited: 75 m/s for the thickest, myelin-sheathed nerves, with added time for jumping synapses. The gap in time between my optic nerve's reporting that my fingers have touched my toes (and my brain state reaching its new pattern as a result) and my spinal column's reporting that yes, there is pressure (and my brain state reaching its new pattern as a result), is an appreciable fraction of the gap between the lightning bolt and the thunderstroke back on Mt. St. Albans.

This morning at dawn I walked the dog along our road. The dog ran to the right, down the hill, to try to eat wild blackberries. The dog ran to the left, up the hill, to sniff out where the deer had slept and the raccoons had walked, and to eat god-knows-what. I ambled along, looking at the dog, watching the dawn light paint fresh colors into the world, and watching my shoes make contact with the asphalt of the road. With each step I could see my shoe hit the asphalt and feel--instantaneously--the pressure of the ground transmitted through the sole of my shoe into the shole of my foot.

I looked left at the dog and felt my left foot my left foot squarely hit the asphalt and felt my right my right foot lose contact as it lifted into the air and... Pain. Pain. Pain in my left ankle. No pressure underneath the outer two-thirds of my left foot. Falling. Falling. My left knee hit the ground. More pain. I rolled. I grabbed, cursing, for my twisted ankle.

But I had felt my left foot hit the ground squarely. For more than a fifth of a second my brain had continued in its normal-walking configuration, and I had continued to feel the normal sensations of walking forward. Only then did nerve signals reporting lack of pressure underneath the left foot, nerve signals reporting sharp pain in the left ankle, and nerve signals from the inner ear reporting downward acceleration wipe the sensations of normal-walking out of my brain and shift its pattern of action from a normal-walking to an "Oh f***!" configuration.

Last week I was driving down the road. I saw, a couple of hundred yards ahead, a hound dog sitting by the side of the road. Its coat was grey, mottled with black. It had the long hound-dog floppy ears. I saw its haunches. I thought maybe its tail was wagging. All in all, it looked remarkably like my mother's dog, Beauty, who is 3000 miles away. "How odd," I thought, as I glanced into the rear view mirror, "that that dog looks so much like Beauty." I looked back: no dog, only a grey garbage bag.

These cracks in my consciousness show me that I--the I that is writing this, at least--do not live in the real world. The sensations that I feel and the objects that I see do not necessarily correspond to things that exist in the external world beyond or even within my skin. Something--let's call it Arnold--stands between my sense organs and myself, and because of its actions the things I think I perceive are not necessarily the things that my sense organs perceive. My eyes see a garbage bag; I perceive a dog. My skin feels an absence of pressure: I feel that my feet are planted on solid ground.

Oh, Arnold is benevolent and useful. It would, one presumes, be confusing and counter to one's reproductive fitness if one always had to consciously compensate for the fact that our brain's reports of our sense perceptions are always more than a quarter second in the past. It is better, one presumes, for Arnold to extrapolate what it thinks one will feel in a quarter of a second and feed that to me now--and then to suddenly and discontinuously correct itself if its extrapolation from current to future sense-data turns out to have been wrong. It is almost always better, for a short time, to see an animal that isn't really there than to not see an animal that is really there--particular if the animal is a large vulpine carnivore. And it would, once again, be disconcerting if at any one instant I could see clearly only the image that is at my fovea, instead of the illusion of comprehensive vision that Arnold paints for me--even though Arnold's interference is what makes magicianship possible, a propensity to be fooled by sleight-of-hand does not diminish one's reproductive fitness unless one plays too many poker games.

But it is philosophically disconcerting to have this gatekeeper-cum-signal-processor standing between me and the world I live in...