What have psychologists learned about perception from optical illusions ?

Explanation:

That an optical illusion somehow interferes with the way we see things. Even simple illusions can completely fool us. If you search out the term, you'll see all kinds of them.

Most critically we see one thing and know another to be true. But knowing the truth doesn't help us. We still see and believe the truth of the illusion.

The correct answer to this open question is the following.

Psychologists learned about perception from optical illusions that the response of the senses, when faced with optical stimuli, is different and can be measured because the human can interpret an optical stimulus as being real.

Gustav Fechner (1801-1887) was a German physicist who developed the science that studied quantitative relations of stimuli and sensations. It is called psychophysics. In 1860, he published the book "Elements of Psychophysics," in which he studies how the perception determines the sensory input.