Optical illusions happen when our brain THINKS it's seeing something different than what's actually there in front of us.
Is the lady young or old?
Optical illusions can also be very simple where the artist uses color and line to create the illusion of movement, space, or form. Victor Vasarely and Bridget Riley were some of the first people to use these techniques in their art work. This type of art is part of the movement known as Op Art.
Josef Albers was an American artist who helped us understand color better. He showed us how colors interact with each other. Below are some examples of how our brain can be "tricked" by color.
These blocks of color make us feel like transparent strips are laying on top of each other.
Here, he uses different blues to make the blue rectangles appear to be transparent and overlapping.