which is generated by the brain, with little attachment to the real world. In this sense, what she experiences is no different from dreaming, drug trips, or hallucinations.
HOW FAR IN THE PAST DO YOU LIVE?
It is not only vision and hearing that are constructions of the brain. Theperceptionof time is also a construction.
When you snap your fingers, your eyes and ears register information about the snap, which is processed by the rest of the brain. But signals move fairly slowly in the brain, millions of times more slowly than electrons carrying signals in copper wire, so neural processing of the snap takes time. At the moment you perceive it, the snap has already come and gone. Your perceptual world always lags behind the real world. In other words, yourperception of the world is like a “live” television show (think
Saturday Night Live
), which is not
actually
live. Instead, these shows are aired with a delay of a few seconds, in case someone uses inappropriate language, hurts himself, or loses a piece of clothing. And so it is with your conscious life: it collects a lot of information before it airs it live. 49
Stranger still, auditory and visual information are processed at different speeds in the brain; yet the sight of your fingers and thesound of the snap appear simultaneous. Further, your decision to snap
now
and the action itself seem simultaneous with the moment of the snap. Because it’s important for animals to get timing right, your brain does quite a bit of fancy editing work to put the signals together in a useful way.
The bottom line is that time is a mental construction, not an accurate barometer of what’s happening “out there.” Here’s a way to prove to yourself that something strange is going on with time: look at your own eyes in a mirror and move your point of focus back and forth so that you’re looking at your right eye, then at your left eye, and back again. Your eyes take tens of milliseconds to move from one position to the other, but—here’s the mystery—you never see them move. What happens to the gaps in time while your eyes are moving? Why doesn’t your brain care about the small absences of visual input?
And theduration of an event—how long it lasted—can be easily distorted as well. You may have noticed this upon glancing at a clock on the wall: the second hand seems to be frozen for slightly too long before it starts ticking along at its normal pace. In the laboratory, simple manipulations reveal the malleability of duration. For example, imagine I flash a square on your computer screen for half a second. If I now flash a second square that is larger, you’ll think the second one lasted longer. Same if I flash a square that’s brighter. Or moving. These will all be perceived to have a longer duration than the original square. 50
As another example of the strangeness of time, consider how you know when you performed an action and when you sensed the consequences. If you were an engineer, you would reasonably suppose that something you do at timepoint 1 would result insensoryfeedback at timepoint 2. So you would be surprised to discover that in the lab we can make it seem to you as though 2 happens before 1. Imagine that you can trigger a flash of light by pressing a button. Now imagine that we inject a slight delay—say, a tenth of a second—between your press and the consequent flash. After you’ve pressed the button several times, your brain adaptsto this delay, so that the two events seem slightly closer in time. Once you are adapted to the delay, we surprise you by presenting the flash immediately after you press the button. In this condition, you will believe the flash happened before your action: you experience an illusory reversal of action and sensation. The illusion presumably reflects a recalibration of motor-sensory timing which results from a prior expectation that sensory consequences should follow motor acts without delay. The best way to calibrate
HOW FAR IN THE PAST DO YOU LIVE?
It is not only vision and hearing that are constructions of the brain. Theperceptionof time is also a construction.
When you snap your fingers, your eyes and ears register information about the snap, which is processed by the rest of the brain. But signals move fairly slowly in the brain, millions of times more slowly than electrons carrying signals in copper wire, so neural processing of the snap takes time. At the moment you perceive it, the snap has already come and gone. Your perceptual world always lags behind the real world. In other words, yourperception of the world is like a “live” television show (think
Saturday Night Live
), which is not
actually
live. Instead, these shows are aired with a delay of a few seconds, in case someone uses inappropriate language, hurts himself, or loses a piece of clothing. And so it is with your conscious life: it collects a lot of information before it airs it live. 49
Stranger still, auditory and visual information are processed at different speeds in the brain; yet the sight of your fingers and thesound of the snap appear simultaneous. Further, your decision to snap
now
and the action itself seem simultaneous with the moment of the snap. Because it’s important for animals to get timing right, your brain does quite a bit of fancy editing work to put the signals together in a useful way.
The bottom line is that time is a mental construction, not an accurate barometer of what’s happening “out there.” Here’s a way to prove to yourself that something strange is going on with time: look at your own eyes in a mirror and move your point of focus back and forth so that you’re looking at your right eye, then at your left eye, and back again. Your eyes take tens of milliseconds to move from one position to the other, but—here’s the mystery—you never see them move. What happens to the gaps in time while your eyes are moving? Why doesn’t your brain care about the small absences of visual input?
And theduration of an event—how long it lasted—can be easily distorted as well. You may have noticed this upon glancing at a clock on the wall: the second hand seems to be frozen for slightly too long before it starts ticking along at its normal pace. In the laboratory, simple manipulations reveal the malleability of duration. For example, imagine I flash a square on your computer screen for half a second. If I now flash a second square that is larger, you’ll think the second one lasted longer. Same if I flash a square that’s brighter. Or moving. These will all be perceived to have a longer duration than the original square. 50
As another example of the strangeness of time, consider how you know when you performed an action and when you sensed the consequences. If you were an engineer, you would reasonably suppose that something you do at timepoint 1 would result insensoryfeedback at timepoint 2. So you would be surprised to discover that in the lab we can make it seem to you as though 2 happens before 1. Imagine that you can trigger a flash of light by pressing a button. Now imagine that we inject a slight delay—say, a tenth of a second—between your press and the consequent flash. After you’ve pressed the button several times, your brain adaptsto this delay, so that the two events seem slightly closer in time. Once you are adapted to the delay, we surprise you by presenting the flash immediately after you press the button. In this condition, you will believe the flash happened before your action: you experience an illusory reversal of action and sensation. The illusion presumably reflects a recalibration of motor-sensory timing which results from a prior expectation that sensory consequences should follow motor acts without delay. The best way to calibrate
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