Researchers at New York University have conducted a rigorous experiment demonstrating that adults who stutter experience fluent speech when they believe they are alone. This confirms that perceived listeners—real or imagined—significantly influence speech fluency challenges.
Stuttering disrupts the normal flow and rhythm of speech, often involving repetitions of words or syllables, sound prolongations, or involuntary blocks that convey effort. It affects more than 70 million people worldwide on a daily basis.
Anecdotal reports have long suggested that stuttering diminishes during private speech, such as talking to oneself or an animal. However, until now, this phenomenon lacked laboratory confirmation, "mainly because it is difficult to create conditions in which people believe that they are truly alone," explains Eric Jackson, a speech-language pathologist and researcher at New York University.
Dr. Jackson and his team designed an innovative experiment to investigate this effect.
The study recruited 24 adult volunteers who stutter. Participants were audio- and video-recorded across multiple conditions: conversational speech, reading aloud, private speech (using deception to foster a sense of solitude), private speech+ (with real-time transcription directing them to speak the same words to two listeners), and a follow-up conversational speech condition.
For the private speech condition, participants tackled challenging computer coding tasks—activities known to prompt self-talk. They were assured no one would listen, though recordings captured everything. Remarkably, stuttering was virtually absent among all 24 participants.
“Stuttering was not observed in more than 10,000 syllables produced during the private speech condition, except for seven possible mild stuttering events presented by three of the twenty-four participants," the authors report. "Conversely, the frequency of stuttering was similar for the other conditions."
Published in the Journal of Fluency Disorders, these findings are observational. Future research will explore why solitude so profoundly enhances fluency. The researchers suspect that fear of judgment or evaluation plays a key role, though other factors are likely involved—many people who stutter also speak fluently on stage, while singing, or in theater performances.
Further studies could reveal when social pressures begin impacting young children who stutter.
