Some Activities For Teaching the Mechanics of Vision

Charles T. Buzek                John Spry School                          
                                2400 S. Sacramento                          
                                Chicago Il 60653                       
                                (312)534-1700

Objectives:

   Students are to learn the relationship of light to vision, how light moves, 
how that affects what we see and some structural aspects of the eye.


Materials Needed:

   Small bowl, coin, and water
   3 by 5 cards
   soup cans with ends removed, aluminum foil, wax paper

Strategy:

   The following three activities will provide a good introduction to the
process of sight:
   Take the small bowl and place the coin in its bottom.  Place it in front of
a student at a distance that first renders the coin invisible to the student.
Pour water into the bowl and the student will be able to see the coin that was
invisible before.
   Each student should have a 3 by 5 card held lengthways and inscribed on one 
end with an X in the left corner and a dot in the right corner.  Students are to 
hold the card at arm's length, closing the left eye and staring at the X with 
the right eye.  Instructed to draw the card closer to their face the students 
will notice something interesting about the image on the right.  Change eyes and 
the phenomenon occurs on the left. 
   Each student should have two soup cans as described.  One can to have one end 
covered with aluminum foil held in place with a rubber band.  The other can to 
have one end covered with wax paper.  Using a pencil point make a small hole in 
the center of the aluminum foil then, holding the aluminum foil can outermost 
with the wax paper can directly behind it (wax paper facing into the other can),
place the cans in front of your eye and you will see an image appear on the wax 
paper. 

Performance Assessment:

   In the first activity explain that light travels in a straight line unless
interrupted by a material with a different molecular structure.  Given this,
can the students explain why the coin seems to mysteriously appear?
   The students must be able to describe the phenomenon and then come up with a 
theory to explain it based on their knowledge of ocular anatomy.  A little 
discussion beforehand wouldn't hurt.
   For the third activity the students must be able to describe the phenomenon
accurately and draw a diagram to explain it.

Conclusions:

   It should be stressed to the students that none of these experiments in any 
way changed the physical world.  The phenomena that we observed occurred only 
within our brains.  The coin did not move, images didn't really disappear or 
appear nor did an object invert itself.  We perceived these things to happen 
because of the nature of our eyes and the way we interpret the information that 
comes to us from them.