LACY GRIGSBY                   Paul Robeson High School
                               6835 S. Normal Avenue
                               Chicago, IL 60621

Objectives: 1)  To have the student to observe and experiment with 
                  visual after images.

              2)  To have the student observe white light and its 
                  component color spectrum.

              3)  Introduce the student to the basic colors and their 
                  complements within the visual system by demonstration.

              4)  Introduce the basic parts of the eye.

              5)  To demonstrate how the optical path and focal system 

              6)  To demonstrate how an image is projected upon the
                  retinal network.
              7)  Show feature analysis of illusions produced by after 

              8)  To show the student how to derive any given color.

Materials:      Candle, convex lens, overhead projector, color light box, 
                  3 by 5 index cards, envelopes, small triangles (red, blue,
                  green, and yellow), drawings or pictures, matches, and model  
                  of the human eye.

Strategies:     Pass out envelopes containing four different colored triangles
                  and an index card.  see below
                                                                  .    ..
                     _______________________________________     ..   . .
                     =          __                         =    . .  .  .
 PA                  =       =      =                      =   .  . .   .
                     =     =          =                    =  .   .......
                     =    =      =     =         =         = ......     .
                     =    =            =                   =      .    ..
                     =     =          =                    =     ..   . .
                     =       =  __  =                      =    . .  .  .
                     =                                     =   .  . .   .
                     _______________________________________  .   .......

                  Have the students in the class place a red triangle in the
                  center of the circle.  (Make sure that the student 
                  concentrates on looking at the triangle for at least
                  45 seconds).  When the time is up have them stare at the dot 
                  on the other end of the card. 

                  You should ask them if they see anything unusual as they are
                  staring at the dot. ans.  (A blue after image). Wait six 
                  minutes then have them try another color on the card.
                  Each time they should see an after image of the 
                  complementary color(s). If you have students that don't
                  seem to see the after image, show them the handouts I
                  gave you or pictures from Human Information Processing
                  page 216a thru 216d.  This may them to see the phenomena
                  and identify the colors.

 Light box=PA     The color light box should be used at this point. Show 
                  the complementary colors, and the white color produced 
      &           when the three basic colors of light are added together.  
                  The triangle of colors should be put on the overhead 
 Triangle=        also, to show the student to derive the other colors 
    chalkboard    and their complements. NOTE The room should be dark.

                  Take the candle and put it about two feet in front of 
 Image=PA         the object you would like to project your image upon.
                  Light the candle. Take the convex lens and move it back
                  and forth between the candle and the screen until you
                  find the focal point. (The candle image should now be
                  projected on the screen in full living color, upside
                  down). This is the time to pull out the model of the
                  eye and show them how the eye works.

                  These PA's should lead to all sorts of wonderful 
                  discussions about photochemicals and proteins, eye
                  structure and function, images and after images, 
                  component colors of white light, and colors and their

References      Lindsey, Peter, and Norman, Donald. Human Information
                 Processing.  New York:  Academic Press, 1973.

                  Otto, James, and Towle, Albert.  Modern Biology  New
                  York:  Holt, Rinehart and Winston, 1977.
Return to Biology Index