From: w.p.coyne@newcastle.ac.uk
Newsgroups: sci.bio
Subject: Mental Models (was "Falling" Asleep)
Date: 24 Jan 93 13:44:52 GMT
Reply-To: w.p.coyne@newcastle.ac.uk
Organization: Chemical & Process Engineering Dept, University of Newcastle, UK.


  I have renamed this as it is getting of the Subject header onto
a slightly different topic.  So unless it is renamed some  of those
interested in it might miss it.  My contribution comes after 
Mickey Rowe's.

rowe@pender.ee.upenn.edu (Mickey Rowe) writes:
       under the Subject: Re: "Falling" Asleep

>In article <C137I6.6Fy@iat.holonet.net> ken@iat.holonet.net 
>     (Ken Easlon) writes:

>>On the other hand, if we perceive the scene to be a part of the
>>gravitationally oriented environment, then we make an extra effort to keep
>>the scene oriented properly with respect to gravity, and perceive our head
>>to be at an angle.

>I'm not sure why I didn't think of bringing this in before, but there
>is a set of experiments that you might find interesting wrt this
>subject.  I can't remember the name of the person who did it, but he
>was at one time a student of George Gerstein's, so I could find out
>pretty easily.  In any case, the experiment was aimed at demonstrating
>how we use some sort of efferents copy in the conversion of visual
>information from an eye centered coordinate system to a head or body
>centered coordinate system.

>This is how the experiment was performed.  A human subject was
>strapped (lying on his back) to a table which could be rotated to
>pitch the head up or down.  During the experiment the room lights were
>turned off, and the subject fixated on a small LED positioned such
>that the subject had to hold his extraocular muscles in tension to
>maintain fixation.  Under the supervision of an anesthesiologist, the
>subject was curarized.  Curare blocks transmission at the
>neuromuscular junction, so the patient had to be respirated and had
>little ability to communicate anything during the experiment.  The
>point of the curare (and the experiment) was that in order to hold the
>eyes fixated on the target, the signals from the oculomotor neurons
>had to continually increase to offset the effects of the curare
>(otherwise the eyes would drift back to their neutral position).

>What the subject experienced during this experiment was that the
>target drifted further and further away from straight ahead position
>even though in fact the target was stationary.  The interpretation is
>that the subject's brain used the oculomotor signal to determine the
>position of the eyes in the orbit, and hence the direction of gaze and
>the position of the target.  One would guess that our brain similarly
>keeps track of a lot of information about head and body position in
>determining the orientation of any visual scene.  Since one of the
>defining features of REM sleep is the chaotic (though, I think,
>primarily horizontal) eye movements, I'd guess that dream "imagery" is
>disconnected from this apparatus.

>Mickey Rowe     (rowe@pender.ee.upenn.edu)

An even simpler experiment anyone can do which demonstrates the 
existence of internal models is as follows. (Sorry can't remember
     the reference. Hopefully it's clear enough an explanation).

   Use your finger to gently press on your eyelid to exert pressure 
   on the side of your eyeball.  This causes the object you are 
   looking at to appear to move.

      The explanation I read was that the brain has a copy of the
   image you are looking at.  If the copy and the image disagree
   this implies something in the image has moved.
   Before your brain isssues a command to 
   move your eyes it creates a model of what you should
   see after the eye has moved.  It can then compare this model
   with the actual image to judge by how much your eyes actually
   moved.

        In the eyeball experiment the brain has issued no eye
   movement commands so its copy is the original image.  The 
   pressure of your finger causes the image coming thru the 
   lens of the eye to change.  The brain "knows" you are not
    moving so it interprets the image as the outside moving.

                                         W.P.Coyne@newcastle.ac.uk 
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