A trivia presentation to boggle the mind of the sleepy training participants. Can be given before or during the lecture or session. This is my personal presentation I gathered from an old Reader's Digest.

1. Can you trust your own eyes?
Don’t be so sure. Check out these
optical illusions and see if you fall
for their trick.

2. 1. Do all of these horizontal lines
actually bend?
The lines are all straight – and parallel. They appear to curve because of
a trick played on neurons in the visual centre of your brain. The retina
sends signals to the part of your brain where edges and lines are
created. But the shapes and shadings of this “café wall” illusion play
havoc with the signals by both exciting and depressing the brain cells. In
trying to interpret the muddled message, the brain decides the lines are
bent.

3. 2. Which step in this staircase is
lowest?
Look for that lowest step and you just go round and round, getting nowhere.
When your eyes and brain take in those straight, two-dimensional lines that
form the staircase, they turn them into three dimensions. But they can only do
this for one part of the picture at a time-say, a corner where the stairs turn and
descend – not for the whole image at a glance. So you keep seeing pieces that
make sense, even though the staircase itself is impossible.

4. 3. Do the lines here form a spiral
The spiral you see doesn’t exist. Instead it’s a series of complete circles. Try
tracing one with a pencil and you’ll see. The slanted black and white
segments that make each line look like twisted cords. Those segments cause
the visual neurons in your brain to signal that the circles slant inwards,
creating a false spiral.

5. 4. Are there dots at the intersection
of the white lines?
No. Your visual neurons are being duped once more, this time by the play of
light and dark. The precise spacing here between the blue corners of the
squares and the white intersections gives the neurons the double whammy.
Some cells are stimulated while others mellow out. The result: grey dots that
seem to appear and then vanish if you look right at them.

6. 5. Which one of the red ball is
smaller?
The red balls are exactly the same size. But the one on the left looks smaller
because we tend to make visual judgments – color, brightness, distance, size
– by comparing nearby objects. In this case, the mind is fooled because one
red ball is small compared to those surrounding it, while the other is large
next to those around it.

7. 5. Which one of the red ball is
smaller?
The red balls are exactly the same size. But the one on the left looks smaller
because we tend to make visual judgments – color, brightness, distance, size
– by comparing nearby objects. In this case, the mind is fooled because one
red ball is small compared to those surrounding it, while the other is large
next to those around it.