Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!tdatirv!sarima From: sarima@tdatirv.UUCP (Stanley Friesen) Newsgroups: comp.ai.philosophy Subject: Re: CoOntinuous vs discrete Message-ID: <191@tdatirv.UUCP> Date: 10 Apr 91 19:19:30 GMT References: <91082.223501DOCTORJ@SLACVM.SLAC.STANFORD.EDU> <1991Mar25.141743.21124@news.larc.nasa.gov> <19175@ogicse.ogi.edu> Reply-To: sarima@tdatirv.UUCP (Stanley Friesen) Organization: Teradata Corp., Irvine Lines: 34 In article magi@utu.fi (Marko Gronroos) writes: >32 bits? Integer? Not floating point? > How about sight? You can see the Sun, which is -27 magnitudes, and a >galaxy that is +6 magnitudes. The brigthness difference is 32 >magnitudes ==> approx. 10^13 ==> 10 000 000 000 000. 32 bits is only >4 294 967 296. > Ok, ok, neurons don't fire 10 000 000 000 000 times as fast when >watching the Sun than when watching a star, but this is just an example >of dangers of using fixed-range numbers. How about using floats?? This is an invalid argument. It is easily established that human sensitivity to light (and to most other stimuli) is *logarithmic* is nature. This is why the magnitude scale is logarithmic. Thus the brain hardly needs to encode such large 'values' as 10,000,000,000,000, it need only encode, say 13 (or perhaps 27). And indeed this appears to be what it does, the values I suggested fall within the observed range of variation in firing rate of neurons. Thus it appears that a single *byte* would be sufficient to encode the data transfered by a single neuron! Essentially the brain seems to use about one digit of mantissa and about three or four digits of exponent. A sort of 'short float' format. >Yes, of course! What a scientific breakthrough! WOW! But exactly >becouse of this they use a rotated '8' - symbol in mathematics and >exponents for smaller numbers. B-> Quite, and this is also essentially what a neuron does. Each neuron has a resting firing rate that could be said to represent an exponent of zero, with a depressed rate representing a negative exopnent and an increased representing a positive exponent. The maximum firing rate, determined by the refractory period of the neuron, represents machine infinity (i.e. MAXVALUE) -- --------------- uunet!tdatirv!sarima (Stanley Friesen)