Many types of speech disorders have either physical or psychological causes. They often involve leaving out, adding, distorting, or substituting sounds. Some of the most common include stuttering, cluttering, dysarthria, voice and speech sound disorders, apraxia, and muteness. Speech sound disorders are much more common in children than in adults.
Stutterers constantly and involuntarily interrupt their flow of speech, prolong vowel sounds, repeat other sounds, and make unnaturally long pauses. Its cause is unknown, but many stutterers exhibit low self-esteem, nervousness, or an aversion to producing certain speech sounds. Cluttering is similar, but it is more of a language disorder than a speech disorder. The person speaks so rapidly that it is difficult to comprehend what is said, transposes sounds, and makes mistakes in both grammar and vocabulary.
Lisping is another form of speech disorder. Interdental lisping is most common, such as pronouncing the words "sink" and "think" alike. There is also the lateral lisp, or "slushy s," and the palatal lisp in which the speaker tries to produce sounds with the tongue on the palate.
Dysarthria is characterized by weakness of the speech muscles. It is often due to brain or nerve damage caused by a stroke, cerebral palsy, or amyotrophic lateral sclerosis (ALS), commonly referred to as Lou Gehrig’s disease. In extreme cases, air does not pass the vocal chords, prohibiting the formation of sound.
Muteness and abnormal speech patterns can also be caused by neurological disorders. In some cases, the area of the brain that controls speech may be malformed or speech organs may have developed improperly. Muteness may also be the result of trauma. Many persons with autism also do not speak or display abnormal speech patterns, such as answering "yes" by repeating the question.
There are also many less common speech disorders. Among them are Parkinson's speech, essential tremor, palilalia, spasmodic dysphonia, selective mutism, and social anxiety. One of the rarest of all speech disorders is dysprosody, or pseudo-foreign dialect syndrome. The speaker with this disorder has difficulty with pitch and timing.
Treatment for speech disorders depends upon the cause. If it is psychological, the patient should be taught how to overcome the mental state that is responsible for the disorder. A speech therapist might be able to help with the problem. If the cause is physical, treatment may involve nerve or brain surgery. In either case, medicine may be prescribed.