November 10, 2006 | David F. Coppedge

Brain Compensates for Eye Movements

Your eyes are continually jumping in little movements called saccades, yet your brain interprets the view as a steady image.  How can that be?  Scientists at the University of Pittsburgh are on the track of finding out “why our shifty eyes don’t drive us crazy.”  They’ve discovered that the signal that sends a command to the eye to jump also sends a compensatory signal to the receiving neurons to shift accordingly.  The circuit is thus complete, and your mind is not even aware of the jumpy eyeballs.  Saccades keep the object of attention centered for high-acuity processing (11/24/2005) and also protect individual rods and cones from saturation (03/29/2002).
    That’s not all.  The scientists say the results of this study will “also provide a framework for studying corollary discharge in other sensory systems, such as hearing: Even when you move your head around, you still hear sounds around you as coming from the same place.”

Though the study was conducted on primates and humans, undoubtedly this is a widespread phenomenon in the animal kingdom.  It probably works similarly, for instance, in birds that bobble their heads as they walk, enabling them to get a smooth picture that maximizes static views during forward motion (see 04/12/2004).
    Studies like this remind us that the optical design of the eyeball, amazing as it is, is just part of a much vaster sensory network.  Vision would be useless without the cooperation of signals, neurons, software and muscles, blood, repair mechanisms, and linkages to all the other systems of the body.
    The eyeball gave Darwin cold shudders, but that was with his coat on.  Piece by piece, with each new revelation, his theory has had to shed its cloak of explanatory power.  There’s not much left.  That’s why he is resorting to hot air to try to keep warm (10/27/2006).

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Categories: Amazing Facts, Human Body

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