Speech production represents a complicated series of events between multiple inputs and outputs, offering several possibilities for breakdown and error. The various nested loops underlying speech production can malfunction in many ways. Different stutterers can stutter for different reasons, an often unrecognized fact that accounts for much of the conflicting data in the speech literature. Further, that which causes stuttering need not be that which maintains it. Until recently, most research has concentrated on the phenomenology of prolongations, repetitions and pauses rather than integrating this data into underlying feedback control systems.
Recent studies demonstrate that stutterers have an abnormal speech-motor control system.
These abnormalities are manifest by the inability to produce appropriate motor adjustment at the rate required for normal speech. It is not known why stutterers have this abnormality. It may reflect compromise at different levels of the neuraxis, in different individuals. Interdisciplinary research should provide a better understanding of the stutterer's speech abnormalities, leading to more successful therapies. Unfortunately, until recently research on stuttering did not lie within the domain of neuroscience.