The Stroop Test is an exercise that measures attention. The premise is pretty simple. The word for a color is written in a color that may or not be congruent with the word itself...
The objective is to identify the actual color of the text. In this case, it's red, even though the text says "green." Sometimes the color matches the text; sometimes it doesn't. In the test, participants are asked to repeat this process over and over, and there's a tally of how many correct responses are given. If you'd like to give it a try, you can do so here.
Semantic processing, your understanding of the word, happens automatically. It takes attention to work through whether the actual color of the text is congruent with what the text says. In an effort to be as quick as possible when performing the exercise, the conflict between reading the word and seeing the color produces errors.
But not if you're hypnotized.
When subjects are hypnotized and given the suggestion that they can't read the text ("These words are written in a language you don't understand.") the people in the study only recognize the color, and they get the color responses correct. The only catch is that the people who have succeeded in the studies are highly hypnotizable. The low hypnotizable subjects didn't fare as well. Here is one of those published studies.
This is a great example of how hypnosis can actually change brain function. In this case, the simple suggestion that they couldn't read the words turned off that function in their brain and allowed them to focus on the colors. This encourages us to look at hypnosis as related, to some extent, to attention and how we allocate brain space and usage to attention.