Let us take this old woman/young girl illusion.
This has been a popular optical illusion that has been circulating for (would you believe?) almost a hundred years. Just like the spinning lady optical illusion, your perception of this image may shift from seeing a young girl, that one would want to take out on a date, to an old sad woman who looks like she could use some comforting.
Through mind-conditioning, two people can see different images from the same picture. Stephen Covey, in his "7 Habits of Highly Effective People," gives a very good example on how a conditioned mind affects how we perceive things.
In a class discussion, Covey presented half of the class with this picture:
Exhibit A
The other half received this:
Exhibit B
Then the participants were shown the "Lady Picture" and each was asked what they see.
True enough, those who received "Exhibit A" saw an old woman in the "Lady Picture," and those who were given "Exhibit B" saw a lovely young girl.