I believe that the concept of an inhibitory or threshold mechanism in stuttering dates back to the early studies. This idea can be viewed through the lens of Sheehan’s “approach-avoidance conflict” theory, which suggests that stuttering results from the conflict between the desire to speak and the fear of speaking. Van Riper proposed that stuttering occurs as a reaction to the efforts to avoid it. Similarly, Johnson argued, “The greater the demand for fluency, or the more you fear or try to fix stuttering, or feel pressured about stuttering, the more likely you are to stutter.” Bloodstein’s Anticipatory Struggle Hypothesis suggests that people who stutter learn to believe that speech is difficult. This anticipation of difficulty speaking can lead to a self-fulfilling prophecy. I recommend checking Evan Usler's (PhD) [podcast](https://www.listennotes.com/podcasts/stuttering/why-stuttering-occurs-the-8vpnU5ENlA_/), or his [research study](https://alliedhealth.ceconnection.com/ovidfiles/00011363-202201000-00004.pdf) (PDF file), or [this ](https://www.youtube.com/watch?v=AES-7ARLYgg&t=9s&ab_channel=PaulBrocklehurst) video (that explains the threshold mechanism), or [this ](https://www.researchgate.net/publication/353636923_THE_VARIABLE_RELEASE_THRESHOLD_VRT_HYPOTHESIS_OF_STUTTERING)research study.