From: rclark@lpl.arizona.edu (Richard Clark x4971)
Newsgroups: rec.arts.sf.science
Subject: Re: Virtual reality, the brain, and high-speed modems.
Date: 10 Apr 92 11:45:22 GMT
Organization: Lunar & Planetary Laboratory, Tucson AZ.

In article <1992Apr7.182053.27694@cs.rose-hulman.edu> kempga@NeXTwork.Rose-Hulman.Edu writes:
>In article <1992Apr7.160153.13146@ux1.cso.uiuc.edu>  
>mjg51721@uxa.cso.uiuc.edu (Michael James Gebis) writes:
>> I have recently read a variety of stories concerning COMPLETE virtual
>> reality where the user has had an implant (or something, sometimes this
>> is not very clear) in his brain which totally simulates all sensory
>> input, and also receives all commands from the brain.
>> My question is....how much information is this?  How fast an interface
>> would be required?  Would a simple parallel port do, or are fiber-optics
>> more realistic?
>
>More information than you think.  Human vision consists of ~10^8 pixels  
>with 16 bits of color information per pixel (humans can distinguish ~14  
>million colors).  Images are processed at about 24 per second.  This comes  
>to about 20 gigabytes per second per person (very rough ballpark figure).   
>That's a whole lotta bits.  Today's best systems are still 1000x too slow  
>for this.  For now, the only way to move that much information is to look  
>at something and let your eyes do the seeing.
>
>> Mike Gebis   mjg51721@uxa.cso.uiuc.edu   OR   m-gebis@uiuc.edu
>--
>Greg Kemp
>inmate, Rose-Hulman Institute of Technology
>Internet: kempga@rosevc.rose-hulman.edu


This may reflect the amount of information that enters the eye but most of
it doesn't get past the retina. It get processed from low level (photons)
to high level (edges, surfaces, motion...). And human vision is pitiful at
absolute photometry, images get processed/compressed into relative brightness.
This processing is distributed from the retina through a couple of
intermediate neural structures before reaching the visual cortex. By this
point the data flow is almost manageable but represents high level information
about the world that the current state of the art in AI can't begin to deal
with.

Much of the dynamic range in scene brightness is achieved through a log
response rather than linear.

Contrasts in brightness/color across edges are handled very well in animal
vision but differences in non adjacent segments of a scene somewhat less so
and from scene to scene not well at all. The reason for this includes the
fact that photoreceptors have horizontal linkages to surrounding receptors
in the retina so that the hardwiring of the retina includes some moderately
complex filters. There is a hierarchy of scales on which different types
of differencing schemes operate. This is just the first stage of vision
processing that the retina does before the information enters the optic
nerve. The information compression just in the eye itself is... 10^6 comes
to mind but I can't find the reference. I think that would include brightness
+color+spatial+temporal compression. (most of vision operates at less than
24 frames/sec although motion rates are retained in the data stream with a
lower update rate than what the retina can respond to.

You can get away with the greatly reduced data flow by the later processing
of images into high level objects like trees, rocks, things with sharp teeth,
etc. So something like 1/3 of the brain is drawn on in one way or another in
vision processing.

Richard Clark
rclark@lpl.arizona.edu