Its definately cognitive. Fake your confidence till you make it, by forgetting you stutter. Stuttering is no more than a tunnelvision, and to get out you focus on the external world while speaking. You dont need to be convinced that you can talk fluently, you are born talking fluently and you are only scared. Prove yourself you dont have to be. Getting out of tunnelvision : multitask what u hear and see to forget ur thoughts. Then move up a level and add observing emotions to your multitasking so you can understand what you want to say without words. This is how regular people speak