The Stroop Effect

The Stroop Effect is one of the most-studied phenomena in psychology. The test is easy to administer, and works in a variety of contexts. The simplest way to see how it works is just to look the following two lists. Don’t read them, instead say the color each word is displayed in, as quickly as you can:

If English is your native language, you should be much quicker at naming the colors of the first list than the second list. Why? Even though the task is to identify the colors, proficient readers can’t stop themselves from reading the words, which slows color identification in cases where the color is different from the word.

But recently, Amir Raz and colleagues noticed that they could reduce and even eliminate the Stroop Effect by hypnotizing participants and suggesting to them that the words were in a foreign language, so they could focus solely on color. In a new experiment, Raz and three other researchers attempted to see if the hypnosis itself was necessary.

Research has shown that hypnosis is only effective when the person being hypnotized is already susceptible to hypnosis. In order for hypnosis to work, the person being hypnotized must be highly suggestible. But what if highly suggestible individuals are offered suggestions without first being hypnotized? Raz’s team reasoned that perhaps the same effect would result.

The team identified 25 highly suggestible individuals, then divided them into two groups. Each group practiced the Stroop task for a few minutes: a word was flashed on the screen, and participants had to press a key on the computer corresponding to the color it was displayed in. Then one group was hypnotized, but the other was not. After hypnosis (or a break lasting the same amount of time), each group received the same suggestion:

Very soon you will be playing a computer game. When I clap my hands, meaningless symbols will appear in the middle of the screen. They will feel like characters in a foreign language that you do not know, and you will not attempt to attribute any meaning to them. This gibberish will be printed in one of four ink colors: red, blue, green, or yellow. Although you will only be able to attend to the symbols’ ink color, you will look straight at the scrambled signs and crisply see all of them. Your job is to quickly and accurately depress the key that corresponds to the color shown. You will find that you can play this game easily and effortlessly. When I clap my hands twice, you will regain your normal reading abilities.

For half the task, they operated under the influence of the suggestion, and for the remainder of the time, they did the standard Stroop task, with no suggestion (half the participants were given the suggestion for the first half of the task, and for the other participants, the order was reversed). This chart shows the level of Stroop Effect for each condition:

Whether or not participants were hypnotized, all showed a diminished Stroop Effect when it was suggested that the words were gibberish. There was no significant difference in the results between hypnotized and non-hypnotized participants.

While the Stroop effect was not completely eliminated in this task, Raz’s team argues that this experiment demonstrates that reading is not entirely involuntary. The experiment is an example of a simple way that individuals who have not been hypnotized can voluntarily reduce the tendency to automatically read the word they are looking at.