138 Optical Illusions & Visual Phenomena by Michael Bach, who has compiled a great assortment, with some explanations.
The Stroop effect
Look at the chart below and say the COLOUR of the word, not the word itself.
Why is it so difficult? Because the right half of your brain is trying to say the color, while the left side of your brain is trying to say the word.
John Ridley Stroop, better known as J. Ridley Stroop, was an American psychologist whose research in cognition and interference continues to be considered by some as the gold standard in attentional studies and profound enough to continue to be cited for relevance into the 21st century. Wikipedia
Can you read this?
|fi yuo cna raed tihs, yuo hvae a sgtrane mnid, too.
Cna yuo raed tihs? Olny 55 plepoe tuo fo 100 anc. i cdnuolt blveiee taht I cluod aulaclty uesdnatnrd waht I was rdanieg. The phaonmneal pweor of the hmuan mnid, aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it dseno’t mtaetr in waht oerdr the ltteres in a wrod are, the olny iproamtnt tihng is taht the frsit and lsat ltteer be in the rghit pclae. The rset can be a taotl mses and you can sitll raed it whotuit a pboerlm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Azanmig huh? yaeh and I awlyas tghuhot slpeling was ipmorantt! if you can raed tihs forwrad it.
So what is this all about? Simply to demonstrate that you do not actually read words as a collection of letters but recognise them even if they are mis-spelt. Your brain recognises the word and strings its recognition together with the other words it has recognised and so “reads” the sentence without having to consider and work out what each jumble of letters means. This is common with many of the brains operations: it takes an input and then matches it against preexisting concepts stored in the brain and so decides what to deliver as a result.