Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site fortune.UUCP Path: utzoo!watmath!clyde!burl!mgnetp!ihnp4!fortune!rpw3 From: rpw3@fortune.UUCP Newsgroups: net.rumor Subject: Re: A Quick Question - (nf) Message-ID: <3663@fortune.UUCP> Date: Fri, 22-Jun-84 04:08:48 EDT Article-I.D.: fortune.3663 Posted: Fri Jun 22 04:08:48 1984 Date-Received: Sat, 23-Jun-84 02:43:03 EDT Sender: notes@fortune.UUCP Organization: Fortune Systems, Redwood City, CA Lines: 106 #R:isrnix:-18600:fortune:9700009:000:5219 fortune!rpw3 Jun 21 23:40:00 1984 Summary: Human brain store ~1000 gigabytes?? Come on! Humans max out well below 80 bits/sec, so no more than ~10-30 Gbyte is needed... (so maybe we got some spares, huh?) Discussion: Actually, quite a bit of work has been done on this by quite a few experimental psychologists. The classic paper on human "bandwidth" is, of course, G. A. Miller, "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information", The Psychological Review, 1956 Miller defines "processing capacity" in terms of "absolute judgments", i.e., the ability to discriminate among stimuli (e.g., "which of the N tones is this tone?"). The information per trial (e.g., correctly picking one of eight tones is 3 bits) is adjusted for error rate: "...the observer is considered to be a communications channel... The experimental problem is to increase the amount of input information and to measure the amount of transmitted information. If the observer's absolute judgements are quite accurate, then nearly all the input information will be transmitted and will be recoverable from his responses. If he makes errors, the transmitted information may be considerably less than the input. We expect that, as we increase the amount of input information, the observer will begin to make more and more errors; we can test the limits of accuracy of his absolute judgaments. If the human observer is a reasonable kind of communication system, then when we increase the amount of input information the transmitted information will increase at first and will eventually level off at some asymtotic value. This asymtotic value we take to be the 'channel capacity' of the observer; it represents the greatest amount of information that he can give us about the stimulus on the basis of absolute judgements..." Plotting many previous experimenters' data (plus some of his own), he shows that the human ability to discriminate stimuli for uni-dimensional stimuli (pitch only, or brightness only, or linear position only) is about 2.6 bits, or correctly picking one of six equally likely choices. The highest capacity channel observed was about 3.5 bits (10-15 choices), when picking pointer positions off a line. [Hmmm... like interpolating between gradations on a meter stick.] The lowest capacity was for taste intensities, about 1.9 bits. With multidimensional stimuli (i.e. pitch AND loudness AND duration, etc.), channel capacity goes up, but even with 6-8 dimensions the information per decision was not more than about 7 bits. By grouping items into sequences, the total information increases, although the information per item goes down, so that short-term memory recalls of 40 bits or so were demonstrated (with the aid of considerable re-coding). The really important contribution of the paper, I am skipping over -- the ability of humans to "re-code" or "chunk" their input, so as to handle more data. (In the memory test above, the "re-coding" was to use octal, hex, and base-32 numbers to remember strings of binary digits.) [Note: this paper has been used as a standard reference to show why, for example, function keys on a keyboard should be clustered in groups of four or five.] Instead, look at what this says about total human bandwidth. As an UPPER limit, let us assume that we can correctly and consistently and continually absorb and process input stimuli at 8 bits per event (higher than ANY shown in the lab!) at 10 events per second (faster than one event per reaction-time). The would put our input processing at 80 bits/second (which is FAR too high!). Note that this has little to do with reading speed, since estimates of the information content of English range as low as 1.1 bits/word, once the contextual environment is built up. (Try cutting every third word out of newspaper stories... you'll be surprised how much is left!) Also, due to re-coding, we are constantly editing our input to maximize the "quality" of those bits. (See Frank Herbert's "Destination Void" for a fascinating discussion of consciousness as mediator of perception. Watch your own mind sometime to see how things in the environment come into your awareness and disappear again, all the time.) Again, 80 b/s is a somewhat excessive upper limit. Try reading and REMEMBERING 10 char/sec of random text, continuously! Even so, at 24 hours a day (no sleep?), 100 years per life, remembering everything perfectly, one needs only about 30 gigabytes of long-term memory. Fits on a couple a Betamax cassetees, easy! [Note: 2 bits/Hz, 75% utilization of each scan line, a good Reed-Solomon code on top of rate-1/2 Viterbi, gives over 1.5 Gbyte per hour of play time ==> ~3.5 six-hour tapes.] (Actually, this makes the science-fiction ideas about personality/learning transfer seem almost attainable, if only...) In fact, the actual data rate and storage are probably far less. I would dare say less than ONE Beta tape! The trick is in coding ("chunking") the data. Anybody want to try and Huffman-code a lifetime? Rob Warnock UUCP: {ihnp4,ucbvax!amd70,hpda,harpo,sri-unix,allegra}!fortune!rpw3 DDD: (415)595-8444 USPS: Fortune Systems Corp, 101 Twin Dolphin Drive, Redwood City, CA 94065