markh@csd4.csd.uwm.edu (Mark William Hopkins) (04/11/90)
In order to reconstruct the underlying architecture of the brain, the ultimate goal of AI, you need to perform tests to determine its functional behavior. In that regard, the brain is just like any other physical system and should be treated as such. It's suprising how far one can go with simple "black box" experiments to test the brain like one would test a transistor or circuit. All you're really doing in the process is a kind of "debugging", only here you don't have the source code or specification. That's a process called Reverse Engineering: by which one derives the design of a system from its functional behavior. We're all aware of the various cycles that we experience (such as the sleep-wake cycle). And based on such experiences we may easily conclude that there is some kind of biological clock in our bodies. One time in my Biology class in high school, our teacher wanted to prove to us that our sense of time was unreliable. What he did was have the entire class time off 300 seconds upon hearing the "GO!" from him. He simultaneously timed off 300 seconds from his watch. The students were asked to raise their hand upon reaching 300. What he suspected was that most everyone would raise their hand prematurely, as was the case. On that basis he would demonstrate just how innacurate we innately were. There was one interesting exception though. When I reached 300 and raised my hand it occurred at exactly the time the teacher said "STOP!". The impulse to raise it actually occurred just BEFORE the teacher said stop, the hand went up just after. To this day I still don't know whether he ignored me or just didn't notice... Now that I thought more about it, it seemed to me that I must have timed off 5 minutes right down to the last 1/10th of a second. This would not be suprising considering that I had lots of practice doing this (with feedback from an actual clock). So that prompted a couple questions: * Is there a clock in the human brain? I mean a clock which behaves like a counter/timer peripheral as it would for a CPU. and * Can you *program* a clock into your brain? Now these questions can be fairly easily resolved by a few simple experiements. I set up such experiments by configuring a microprocessor to clock input signals from a push-button (which had already been installed for another project). The microprocessor was capable of clocking the interval between two push-button signals down to the last instruction cycle (1 microsecond). The signal delay was a small fraction of an instruction cycle. The only non-repeatible deviation lie in my internal clock and in the control of my hand, so I had complete "control" over the deviation. This is a very simple experiment to set up: it only took a few minutes to program the machine in question and to whip up a simple driver program to process statistics, display results and drive the process. If you have a processor at hand, it is something you may want to try yourself. The first experiement was to determine how well the brain could resolve time. The means to do this was to try and clock off intervals from the push button as close to a predetermined number of machine cycles (600,000) as possible. The time was kept small for this experiment (600,000 cycles is about 0.6 seconds). A feedback loop was established by displaying the error (Actual time clocked off minus the target time), and a running average and RMS deviation were continually displayed. The goal was both to determine how well time could be resolved (using the RMS deviation as an indicator), and to determine how well the brain could be TRAINED to resolve time (using the feedback). The way averages and RMS deviations were computed were as "decaying" averages. The effect of each trial decayed exponentially with subsequent trials with a "time-constant" set so that the "half-life" would be 10 trials. This enabled me to observe the trend in the RMS deviation (and average) while still allowing the averaging to take place in a meaningful manner. The result: initially I was able to clock off intervals with an RMS deviation of around 40,000 cycles (microseconds). With about an hours' practice I managed to establish control to within a 25,000 microsecond deviation. This value varied widely and heavily depended on my degree of concentration. It was very easy to "let go" and let the value slip back up to the 40000 to 50000 range. However, there were times in which I could (somewhat inconsistently) establish control to within 5000 microseconds. The tentative conclusion of this part of the experiment was that (1) The brain could be trained to resolve time, and that (2) with enough practice this resolution could ultimately be carried down to a plus-or-minus 5000 microsecond figure at which point one runs into a biological limit. That is consistent with the assumption that there is a 100Hz clock in the brain. The second experiment was to determine how well the brain could clock units of time over a longer period. The cycles were set to 1 second, and the period in question was set to 5 seconds. The goal was to train an internal second counter to achieve the accuracy of a clock. This would establish that there is an oscillator in the brain which can be used to drive a clock. The same feedback control and statistical technique was used here as in the previous experiment. This experiment was cut off before completion (it is difficult to establish that many trials with a 5 second cycle time), so the results are tentative. Initially, by counting to 5, I could establish control to within about 500,000 cycles (1/2 second). With practice, I managed to get this RMS deviation down to around 150,000 cycles. Maximum concentration allowed me to tentatively establish control to under 50,000 cycles, but this was difficult to maintain for any length of time. There were a definite subjective experiences that correlated with the increased control. Gradually, this sense of being able to "see" intervals like spans. Also, the ability to "hear" the interval elapsing (a continuous sound that lasted a given duration marked an interval), evolved. It is interesting that I could achieve much better control when using these indicators and "feeling the wait", instead of counting off the cycles. of spatial distance emerged. OTHER QUESTIONS: There are interesting experiences of mine that have prompted other related issues about internal counter/timers in the brain. I've classified them as follows: (1) CROSS-TALK: How many counters (not necessarily running at the same period) can you have "running" in your brain at once without interference? I've succeeded in getting two to run at once on different occasions. This brings up a related point. There are often times when I may be thinking of a musical sequence when suddenly a song appears on TV or the radio. All of a sudden, I find myself completely incapable of continuing the sequence I had in mind originally due to the interference. How many strands of music can one have running in the mind at once without mutual interference? How far can this skill be developed? As you know, this is what is involved in learning to play both the upper and lower registers on a piano; it's what is involved in composing intricate harmonies, like those of Bach. (2) SUBLIMATION: There have been occasions in which I have "set up" an internal counter in my mind and I would forget all about it. Moments later I'd suddenly become aware of going "...756, 757, ..." and realise that I forgot to "shut off" the timer. If you can sublimate that counter/timer like this, then what's controlling the process when it's completely unconscious? Where's the "oscillator"? And just how far can this "sublimation" be carried out?
wcalvin@milton.acs.washington.edu (William Calvin) (04/11/90)
Re human timing experiments: 10 millisec is pretty
good for jitter, about the limit of the motor neurons that run the
muscles. But there are occasions when one can do much better, as in
throwing a ball, timing the release to less than a millisecond (you
can work backward from the physics to estimate a launch window).
So how can the system perform better than the most precise of
its individual elements? Averaging. In sound localization, you can
detect interaural arrival times down about 10 microseconds. That's
because you can average over hundreds of repetitions of the waveform,
taking many milliseconds before arriving at the judgment of sound direction.
But for throwing, you can't average that way: you must use an ensemble
average, averaging the recommendations of hundreds of timers that are all
trying to accomplish the launch window time. To cut the jitter in half,
you just use four times as many timers. Given the intrinsic jitter of
the best of individual neurons (when acting as pacemakers, rather than
merely reacting to an input) in the 10 millisecond range, you need a
ten-fold reduction to get the jitter under 1 msec -- and that means a hundred
such timers.
If your library has the JOURNAL OF THEORETICAL BIOLOGY, see my
article on throwing in the September 1983 issue. Or Mile 144-155 of my
book THE RIVER THAT FLOWS UPHILL (Sierra Club Books 1987). Or Ch.10 in
my new book THE CEREBRAL SYMPHONY: SEASHORE REFLECTIONS ON THE STRUCTURE
OF CONSCIOUSNESS (Bantam, 1989).
William H. Calvin wcalvin@u.washington.eduthornley@cs.umn.edu (David H. Thornley) (04/11/90)
In article <3376@uwm.edu> markh@csd4.csd.uwm.edu (Mark William Hopkins) writes: > > In order to reconstruct the underlying architecture of the brain, the >ultimate goal of AI, you need to perform tests to determine its functional >behavior. In that regard, the brain is just like any other physical system and >should be treated as such. It's suprising how far one can go with simple >"black box" experiments to test the brain like one would test a transistor or >circuit. All you're really doing in the process is a kind of "debugging", >only here you don't have the source code or specification. That's a process >called Reverse Engineering: by which one derives the design of a system from >its functional behavior. > ... > One time in my Biology class in high school, our teacher wanted to prove to >us that our sense of time was unreliable. What he did was have the entire >class time off 300 seconds upon hearing the "GO!" from him. He simultaneously >timed off 300 seconds from his watch. The students were asked to raise their >hand upon reaching 300. > > What he suspected was that most everyone would raise their hand prematurely, >as was the case. On that basis he would demonstrate just how innacurate we >innately were. > > There was one interesting exception though. When I reached 300 and raised my >hand it occurred at exactly the time the teacher said "STOP!". The impulse to >raise it actually occurred just BEFORE the teacher said stop, the hand went up >just after. To this day I still don't know whether he ignored me or just >didn't notice... > > Now that I thought more about it, it seemed to me that I must have timed off >5 minutes right down to the last 1/10th of a second. This would not be >suprising considering that I had lots of practice doing this (with feedback >from an actual clock). I doubt the teacher could possibly have been that accurate. Without great care, you can't use a watch to time more accurately than about a second. There is no reason that the biology teacher would take such care for this demo. I suspect that the GO!-STOP! delay could best be described as 299-301 seconds. Therefore, the precision of your response was either partly chance or some other synchronization mechanism was in effect. > > So that prompted a couple questions: > > * Is there a clock in the human brain? I mean a clock which behaves like a >counter/timer peripheral as it would for a CPU. > >and > > * Can you *program* a clock into your brain? > >[description of interesting experiment omitted] > >OTHER QUESTIONS: > > There are interesting experiences of mine that have prompted other related >issues about internal counter/timers in the brain. I've classified them >as follows: > >(2) SUBLIMATION: > There have been occasions in which I have "set up" an internal counter in >my mind and I would forget all about it. Moments later I'd suddenly become >aware of going "...756, 757, ..." and realise that I forgot to "shut off" the >timer. > If you can sublimate that counter/timer like this, then what's controlling >the process when it's completely unconscious? Where's the "oscillator"? And >just how far can this "sublimation" be carried out? Back in my bachelor days, I broke my kitchen timer. I then discovered that I could tell myself how long to cook something, put it in the oven, and then I would have an impulse to look at my watch at the desired time. This impulse occurred no matter how involved I was in any other project, and was sufficiently reliable so that I did not need to replace my kitchen timer for years. The impulse when I was most fully absorbed in something else was typically no more than a minute off what I had "set." What's controlling the process and where's the oscillator? Beats me! How far can this "sublimation" be carried out? The "timer" worked regardless of how occupied my conscious mind was, and in fact seemed to work slightly better when I forgot about it. David Thornley