Stuttering, a speech disorder that affects the fluency of speech, has long been a subject of fascination and misconception. While our understanding of the condition has evolved significantly, one of the most enduring myths about stuttering is that it can be triggered or worsened by criticism. In this blog, we’ll explore the many possible causes of stuttering and delve into a controversial experiment from 1939 that aimed to prove that negative reinforcement could induce stuttering. Spoiler alert: the results were quite unexpected.

Stuttering is a complex and multifaceted condition with various potential causes. It can often run in families, suggesting a genetic component that affects the language center of the brain. Brain injuries, such as strokes or trauma, can also lead to stuttering. Moreover, many young children may stutter as a normal part of their language development but eventually outgrow the issue. In some rare instances, emotional trauma can be linked to stuttering. However, one thing that it’s not caused by is criticism.

The Infamous Stuttering Experiment

In 1939, Mary Tudor, a graduate student at the University of Iowa, along with her faculty advisor, speech expert Wendell Johnson, conducted an experiment that sought to prove that stuttering could be taught through negative reinforcement. For more than four months, 22 kids without parents were promised speech help, but instead, they were used in a study about stuttering. Shockingly, none of the children received actual speech therapy, and only about half of them were genuine stutterers.

The Four Groups

The children were divided into four groups:

  • Half of the stuttering children were given negative feedback.

  • The other half of stuttering children received positive feedback.

  • Half of the non-stuttering children were falsely told they were beginning to stutter and were criticized.

  • The remaining non-stuttering children were praised.

Surprising Results

The results of the experiment were eye-opening. The only group significantly impacted by the experiment was the third group – those non-stuttering children who were falsely criticized and told they were beginning to stutter. Strikingly, despite never actually developing a stutter, these children began to exhibit low self-esteem and adopted self-conscious behaviors commonly associated with stutterers. However, those who did stutter did not cease to do so, regardless of the feedback they received.


While the experiment from 1939 had significant ethical issues and failed to prove its hypothesis, it did highlight the power of perception and self-esteem. Today, we understand that stuttering has a complex set of causes, none of which include criticism as a primary trigger. Stuttering is a condition influenced by genetics, brain function, and various environmental factors. By debunking these myths, we can pave the way for a more compassionate and understanding approach to supporting individuals who stutter, emphasizing empathy, and acceptance over unfounded judgments.

Next: From Prisoners to Heroes: A Tale of Unsung Heroes


  • Rotter, Julian B., Shephard Liverant, and Douglas P. Crowne. “The growth and extinction of expectancies in chance controlled and skilled tasks.” the Journal of Psychology 52, no. 1 (1961): 161-177. [Paper]
  • Wilson, F. A., and E. T. Rolls. “Learning and memory is reflected in the responses of reinforcement-related neurons in the primate basal forebrain.” Journal of Neuroscience 10, no. 4 (1990): 1254-1267. [Paper]

By The Research Mind

We, researchers from the University of Oxford and University of Cambridge, are dedicated to sharing the latest updates, breakthroughs, and even the occasional blunders in Science & Technology. Stay tuned for some truly mind-blowing science experiments!

2 thought on “Controversial experiment on negative reinforcement & stutter”

Leave a Reply

Your email address will not be published. Required fields are marked *