Effect of Eye Position on Perception

[P3D Ronald W Doerfler <doerfler@xxxxxxxxxxxxxxxxxxxx>]

Hi all,

I just saw this news item and thought it was interesting, particularly
the last line:

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        SAN FRANCISCO, April 9 (UPI) -- Italian and U.S. researchers say  
conventional wisdom on how you see things is wrong. 
        It has long been thought that the perceived location of objects in  
relation to the observer depends only on the image reflected in the 
eye's retina -- but the latest evidence shows that's just not so. 
        It also depends on the direction of the gaze. To ensure that the  
visual world remains stable as we look around us, in addition to the 
retinal image, the brain must also take into account the movements of 
the eyes and head. 
        In two reports in the British journal Nature Wednesday, researchers  
from the Istituto di Neurofisiologia del CNR in Pisa and the Universita 
di Roma ``La Sapienza'' in Rome and the University of California, Los 
Angeles, say there's a lot more to seeing things than meets the eye. 
        David Burr of the Pisa center says, ``Conventional wisdom has it that  
the perceived spatial relationship between visual stimuli depends on 
retinal information alone -- and does not require any extra information 
about eye position or the direction of the gaze. Conventional wisdom is 
wrong.'' 
        The teams show that the perceived alignment of objects in the visual  
field is systematically shifted in the period immediately before the so- 
called ``saccades'' -- the sudden movements of the eye that alters the 
position of the entire visual field. 
        Says John Schlag of UCLA, ``In this way, information about eye  
position can modify not only the perceived relationship of the entire 
retinal image to the observer but also -- and this is the surprising part 
-- the relationship between elements within the image itself!'' 
                
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Perhaps one aspect of this is the observations made on this list that
we unconsciously move our head back and forth to find depth information
when we are looking at a scene far away.  This was something I had
never thought about, or had unconsciously assumed to be just trying
to get a better look, until I joined this list several years ago.

(Another similar phenomenon in such a case is squinting when looking
far away, which I believe provides a better focus by decreasing the 
aperture of the eye--the things we do without thinking about them!).

Anyway, the above news item also has implications for viewing through
a stereo viewer, if it indeed refers to depth information.  Certainly,
I find people unconsciously tilt a viewer up or down to mimic the
viewpoint of the camera when the picture was taken.  I don't know
about any confusion relating to a fixed view regardless of gaze
or head position.

Ron Doerfler
rdoerfler@xxxxxxxxxx


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