ABSTRACT
The evolution of a theory or changes in it is not necessarily an indication that its original formulation was incorrect. In the Packman and Attanasio 3-factor causal model of moments of stuttering, the three factors that are proposed as the necessary and sufficient conditions to cause a moment of stuttering are a neural processing deficit that renders the speech production system unstable, triggers, which are inherent features of spoken language that increase motoric demands on the deficient speech neural processing system, and internal factors that vary and determine the thresholds of the triggers. Extended GODIVA model is a well-documented example of the evolution of theory over time. In 2013, Brocklehurst, Lickley and Corley published a paper that described their newly formulated Variable threshold release (VRT) hypothesis. The authors described the VRT as a combination of Bloodstein's anticipatory struggle hypothesis (AS) and the 2003 version of Howell's EXPLAN hypothesis.
