The optic disk is where axons of a retina's cells come together
to form the optic nerve. The optic nerves of each eye meet at the
optic chiasm. For each optic nerve, temporal-side axons continue
along on the same side of the brain to the Lateral Geniculate Nucleus
(LGN), while nasal-side axons cross over at the optic chiasm to
the other side of the brain, on their way to the LGN on that side of the brain.
From both halves of the LGN, the connections continue on to visual
cortex, where vision occurs.
Because there are no receptors where the optic disk is located, we
have a blind spot in each of our eyes. This experiment will help you
to map your blind spot for each eye.
1.) Start by clicking on the 'Start Experiment' button below. A new frame will
pop up. (Note: if you are using Netscape on HP-UX, you should not resize the
new frame. If you are using MS Internet Explorer or a PC version of Netscape,
you may want to resize your new frame to be about as big as
your monitor's screen - but not bigger. Also, if you are using either MS
Internet Explorer or a PC version of Netscape, you will need to click your mouse
somewhere inside the new frame to get things rolling for either of these 2
platforms.)
2.) When the new frame pops up, you will see fixation crosses on either
side of the frame. To map the blind spot of the right eye, close your left eye
or cover it with a patch and fixate your right eye on the cross on the left
side of the screen. To map the blind spot of the left eye, close your right eye
or cover it with a patch and fixate your left eye on the cross on the right
side of the screen.
Sit about arm's length from the monitor.
3.) There will be 200 trials. On each trial a white dot will be displayed.
Your task is simply to press the number '1' on the keyboard if you see the
white dot. If you don't see the white dot, press the number '0'.
Pressing '1' or '0' records your response for the trial and brings up the
next trial automatically.
4.) When finished with the experiment, click 'Plot' in the 'File' menu. You
will see a rectangular grid of white dots, but some of the white dots will
be missing from this grid. The white dots displayed represent the white
dots you saw during the experiment, while the missing ones represent the white
dots you didn't see - thus mapping the blind spot of your eye.