The optical illusions below illustrate how what is perceived is not always reliable. In trading, this can translate into what is known as "confirmation bias"
i.e., seeing what one wants to see. For this reason, visual techniques (alone) should not be the basis for technical analysis.
Look at these grey circles. They look bent, right? Like somebody put a ring in a vice and squeezed it?
Actually, it's just an optical illusion. Both circles are perfectly round.
The picture below is comprised of perfect black and white squares - Really! Test it by aligning the straight edge of a piece of paper with a horizontal line on the image.
Stare at the picture below and you'll see illusory streaks of light at 45 degree angles
Count the black dots...
Focus on the center dot and move your head forward and backward relative to the screen. If you think the picture is animated, print it out and repeat the process looking at the paper.
Get relatively close to the screen and concentrate on the "+" at the center. The green dot will erase the violet dots. The REALLY weird thing about this one is that there is no green dot at all!
The blue lines form three perfect squares - Guaranteed!
These are also perfect squares