The famous Stroop Effect is named after J Ridley Stroop who discovered this controversial phenomenon in the early twentieth century. This experiment consists of the individual reading the color or ink of the word instead of the word. A good quality example is the word "RED" printed in yellow ink. The individual should say yellow instead of red. This exercise becomes so tricky for the mind due to the fact that the words themselves have a strong effect on your ability or effectiveness to say the word. The interference or confusion between the information your brain receives causes a great confusion. Due to this great confusion two main theories have been developed the theory of speed processing and selective attention theory. The speed processing theory consists of the fact that words are identified and processed quicker than color so when you are instructed to read the color your brain processes the information slower. The other theory that was developed due to this effect consist of the confusion occurring because it requires more attention to identify colors and name them than just reading words, this theory is known as the Selective attention theory. As the mind becomes more developed and reading becomes more of a daily activity, this experiment confuses the mind even more. If this experiment were to be conducted on an illiterate person or a child that does not know how to read at a decent level this experiment would come very easily to them since colors are easier for them to recognize than words.The confusion in the brain occurs in the cingulate area. This area of the brain lies between the left and right portions of the frontal brain and is responsible for some of the thought process and emotional responses.

Source: "Neuroscience for Kids" / http://faculty.washington.edu/chudler/words.html