From: rowe@pender.ee.upenn.edu (Mickey Rowe)
Newsgroups: sci.bio
Subject: Re: "Falling" Asleep
Date: 21 Jan 93 21:35:53 GMT
Organization: University of Pennsylvania

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

>This brings up the complicating factor of "correct orientation with respect
>to the head".  I maintain that in waking consciousness, if the image is not
>viewed as being a feature of the earthly environment, we tend to orient it
>with respect to the head regardless of the orientation of the head.  

I think we could really use the input of some astronauts here...
Under most circumstances our brains keep track of our position and
orientation with respect to the ground or floor, so there aren't many
situations in which we can view things independent of the features of
the environment.

>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.

>In my dream experience, vertical alignment (standing up) is the predominant
>mode.  It seems to take a special kind of energy or stress to disorient my
>dream imagery to off-vertical.  

Last night I had a dream where I was on a beach.  Part of the time I
was reclining on the sand, part of the time I was floating on my
stomach, and part of the time I was swimming on my back.  This isn't
uncommon for me.

>Go to sleep upside down, and then see if the world
>looks upside down during the first fraction of a second after you wake up
>:-)

Aw, if only I were Batman :-)

But seriously, since we're back to a public forum, does *anybody* else
understand what it means to say that your "dream" head and your real
head are lined up?  My dreams don't seem to exist in the same space as
my waking life, which is why I've lost track of what this is supposed
to mean...

>Ken Easlon

Mickey Rowe     (rowe@pender.ee.upenn.edu)
Newsgroups: sci.bio