The onset of stuttering in previously fluent adults, without history of any stuttering during childhood, is usually seen in neurologic disease, but also can occur in psychogenic disturbances. These acquired stutterers have dysfluencies throughout their sentences, including the beginning, middle and ending of words as well as phrases. Further, unlike developmental stutterers, acquired stutterers seldom improve with singing, loud broadband noise, or repetitive reading of the same passage. Acquired stutterers usually have small lesions within either hemisphere of the brain, anteriorly or posteriorly. Developmental stutterers usually have a disturbed affect associated with their dysfluent speech, whereas acquired stutterers are usually not bothered by their abnormal speech.
Several researchers suspect auditory dysfunction in stutterers.
The motoric aspect of persons with developmental stuttering has gained increasing research attention. Kinematics, acoustic and aerodynamic studies of individuals with dysfluent speech has furnished data suggesting that developmental stutterers may have subtle motor disruptions even when they are fluent, exhibit muscle synergies such as co-contraction of agonist and antagonist muscles which are incompatible with efficient organization of movement, and have both temporal and spectral deviations from the intended target as the immediate cause for repetitive oscillatory behavior. Functional neuroimaging is another promising avenue of future research, but thus far has had controversial results. Psychiatrically-oriented therapies are ineffective. Recently, newer pharmacologic medications have been employed to help stutterers.