Dr. Schwartz discovered the physical cause of stuttering accidentally while using an ultrasound device to study throat movements in patients with cleft palate. He observed that the vocal cords would forcibly constrict just before every stutter. Further examination revealed that stuttering is caused by a locking of the vocal cords. Various stuttering behaviors, such as hesitations, repetitions, and prolongations, are learned reactions to overcome the locked vocal cords. Dr. Schwartz realized stuttering is a learned reflex triggered by a particular nerve impulse pattern when vocal cord tension reaches a locking threshold, believed to be an inborn reflex.