1. Read all the words from right to left, down the chart. Do that now.
That was pretty easy and I bet you did that pretty fast.
2. Now, say out loud the color of the letters of the word. Don’t worry about what the word is, just its color. Go!
I bet you found that to be surprisingly difficult. You made pauses as you corrected yourself. The reason is that you are challenging your left (logical) brain that wants to read the words and your right (creative) brain that is trying to identify the colors. In this monumental battle,the brain that wants to read the words has a slight edge, because we read words so much more in our daily activities. This is why you have no problem reading them the first way, but a bit of a struggle when you try and say the colors.
The effect is named after John Ridley Stroop who first published the effect in English in 1935.
The best succinct way that I found to explain this was a taken from the following website: http://www.rit.edu/cla/gssp400/sbackground.html “Since the original study, the Stroop effect has been investigated in a variety of ways. One general finding is that the Stroop effect is very robust. For example, the Stroop effect extends to color-related words (e.g. sky and fire). It extends to non-words that sound like color words (e.g. wred and bloo). It occurs with the words are presented suboptimally (dim, faded, small, etc.). It is resistant to practice. In summary, the difficulty of removing the interference effect of the Stroop task has led some researchers to claim that the brain is wired to recognize words without effort. This explanation is called the “automatic word recognition hypothesis” (or automaticity hypothesis), and it is so widely accepted that it is often given, in psychology textbooks, as the only answer to the Stroop effect. According to this theory, reading is an automatic process, which cannot be turned off. In other words, people see the meaning or words without much effort or consciousness. On the other hand, naming colors is not automatic. It requires more effort than reading, thus creating interference in the Stroop task.”
There is so much information on the web if you would like to continue researching more about this. Here are 2 websites I recommend: