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From: David E. Weldon, Ph.D. <David.E.Weldon@DaytonOH.ATTGIS.COM>
Subject: Re: Chaos and Computation
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References: <3pvmlm$o1v@ns1.CC.Lehigh.EDU>
Date: Mon, 29 May 1995 06:55:36 GMT
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}==========x011@Lehigh.EDU, 5/24/95==========
}
}In article <3pj7gc$5u5@remus.reed.edu>, tcarpent@reed.edu 
}(jfaludi) writes:
}>In article <D8MqGE.6on@intruder.daytonoh.attgis.com>
}>David E. Weldon, Ph.D. 
}<David.E.Weldon@DaytonOH.ATTGIS.COM> writes:
}>
}>> There is a facinating relation between "alpha" wave frequency 
}(10 Hz) and
}>> serveral perceptual phenomena that suggest that our brains 
}sample the
}>> environment every 100 msec. and process the sample during 
}that period.  The
}>> brain, in short, freezes the world every 100 msec., taking in 
}frames of
}>> information, along with additional data on motion in the visual 
}field.
}>
}>
}>Pardon me, but this seems fishy.. could you post/email your 
}sources?
}>
Glad to...The phenomenon is called the "Perceptual Moment" and the seminal
article is by Stroud (1956); i.e., Stroud, J.  The fine structure of
psychological time.  In H. Quastler (ed.), INFORMATION THEORY IN PSYCHOLOGY. 
Glencoe, Ill:  Free Press, 1956
An article which argues against the "Perceptual Moment" hypothesis is:

Kolers, P. A. The illusion of movement.  SCIENTIFIC AMERICAN, 1964, vol. 211,
98-106.

There are reasons why Kolers' paper is flawed, but I can't go into it here. 
Send me an e.mail message and I'll give you all the info I've got right now.

}>...You see, if we sampled data at a rate of 100msec, that would 
}only be
}>a sampling frequency of 10KHz.  Considering that we can hear 
}sounds up
}>to 22KHz, and that you need to have your sampling frequency be 
}at least
}>twice the frequency of whatever you want to accurately sample, 
}this
}>would seem to say we must intake information at at least 44KHz.
}>  ..Or were your studies just talking about visual information? (I
}>assume the different sense organs input at different rates.  But I
}>would also assume that visual input would need to be faster than 
}any
}>other input, considering how much we rely/ed on it for moving, 
}hunting,
}>etc...)
}>  But perhaps the example that I'm thinking of (how normal 
}computers
}>input sound) isn't relevant to the way we biologically input 
}sound, and
}>so it's not a problem.

The fastest neuron in the human body functions at 1000 hz maximum.  The 100
msec. (10 hz rate) period is a CNS phenomenon.

}>
}>   ---Jer
}>
In vision, our ability to see is dependent on the speed of recovery of the
rods and cones (the chemical transducers in the retina).  The speed of
recovery relates to the speed of the rhodopsin-vitamin A cycle, the background
illumination, and which visual system is dominant--scotopic or photopic.  As a
rough approximation, in a totally dark room you can see roughly 3 flashes per
second when the flashes are at threshold luminosity ).  In bright daylight,
you can detect flashing (instead of a steady light) up to 50 flashes per
second; after that, the light appears to be a steady light.  Interestingly
enough, subjects in these experiments never report seeing more than 10 flashes
per secong which is consistent with the CNS' Perceptual moment.  Incidently,
the point at which the flashes become a steady light is called, "the Critical
Flicker Frequency" or "the Critical Fusion Frequency" (the CFF).

So at the level of signal transduction, we can possibly see up to 50 changes
in the visual stimilation every second, but at the CNS level, this granularity
is reduced to 10 per second.  The reference for this is, "Harter and White
(1969).  I'm sorry, I don't have the full reference.


