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Scientists Use Post-Hypnotic Suggestion on the Stroop Effect

Tuesday, September 22, 2009 by: Steve G. Jones, Ed.S.
Tags: hypnosis, health news, Natural News

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(NewsTarget) The field of psychology uses various instrumental studies to examine cognitive processes. These processes are either controlled or automatic. Further, automatic processes can either be innate or learned. When a process is automatic, it is performed automatically and unintentionally by the brain. An example of an automatic process is reading. Psychological studies use hypnotic suggestion to determine the connection between the brain and automatic processes.

One such instrument is the Stroop task. When words of colors appear with a congruent color ink, it is easy for the brain to process it because reading is an automatic process. For example, when the word RED is written in red ink, both the meaning of the word and the color of the ink are automatically processed.

The Stroop task asks participants to ignore the meaning of the word and focus on the color of the ink. When presented with the word BLUE in red ink, the brain wants to automatically process what it reads instead of ignoring the color. When the word and ink color are incongruent, it is more difficult to process and is more likely to be inaccurate.

Hypnotic and post-hypnotic suggestion have been used to study the Stroop effect and automatic processes. Raz et al. (2002) studied both highly suggestible and low suggestible participants after using a post-hypnotic suggestion that told them they would have difficulty reading the words. Results showed that the low suggestible participants were not influenced by the post-hypnotic suggestion. However, the highly suggestible participants were better able to process the incongruent examples of the Stroop test. It was also concluded that the post-hypnotic suggestion does not alter vision; for example, it does not cause blurring or tell the participant to focus on a different location (MacLeod & Sheehan, 2003).

In a separate study, Raz et al. (2005) studied the Stroop effect on functional magnetic resonance imaging (fMRI) and electrical scalp recordings (ERPs). The resulting brain images showed that when participants had received a post-hypnotic suggestion, there was less conflict-related activity in the anterior cingulate cortex area of the brain.

When looking at the occipital cortex (processes visual information) in the back of the brain, the activity is drastically different depending on whether the post-hypnotic suggestion is given or not. Raz concluded that when a post-hypnotic suggestion is given before the Stroop task, the occipital cortex receives altered information and thus reduces activity in the anterior cingulate cortex. Eliminating the Stroop effect has important implications in the fields of neurology, psychology, and hypnosis.


MacLeod, C.M. & Sheehan, P.W. (2003). Hypnotic control of attention in the Stroop task: A historical footnote. Consciousness and Cognition, 12(3), 347-353.

Raz, A., Shapiro, T., Fan, J., & Posner, M. I. (2002). Hypnotic suggestion and the modulation of Stroop interference. Archives of General Psychiatry, 59, 1155-1161.

Raz, A., Fan, J., Posner, M. I. (2005). Hypnotic suggestion reduces conflict in the human brain. Proceedings of the National Academy of Sciences of the United States of America, 102, 9978-9983.

About the author

Steve G. Jones, Ed.S. has been practicing hypnotherapy since the 1980s. He is the author of 22 books on Hypnotherapy. Steve is a member of the National Guild of Hypnotists, American Board of Hypnotherapy, president of the American Alliance of Hypnotists, on the board of directors of the Los Angeles chapter of the American Lung Association, and director of the Steve G. Jones School of Clinical Hypnotherapy.
Steve G. Jones, Ed.S. is a board certified Clinical Hypnotherapist. He has a bachelor's degree in psychology from the University of Florida (1994), a master's degree in education from Armstrong Atlantic State University (2007), and is currently working on a doctorate in education, Ed.D., at Georgia Southern University. Learn more at:

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