Stuttering is generally not a problem with the physical production of speech sounds (see Voice disorders) or putting thoughts into words (see Dyslexia, Cluttering). Despite popular perceptions to the contrary, stuttering does not affect and has no bearing on intelligence. Apart from their speech impairment, people who stutter are normal. Anxiety, low confidence, nervousness, and stress therefore do not cause stuttering, although they are very often the result of living with a highly stigmatized disability.
The disorder is also variable, which means that in certain situations, such as talking on the telephone, the stuttering might be more severe or less, depending on the anxiety level connected with that activity. In other situations, such as singing (as with country music star Mel Tillis or pop singer Gareth Gates) or speaking alone (or reading from a script, as with actor James Earl Jones), fluency improves. (It is thought that speech production in these situations, as opposed to normal spontaneous speech, may involve a different neurological function.) Some very mild stutterers, such as Bob Newhart, have used the disorder to their advantage, although more severe stutterers very often face serious hurdles in their social and professional lives. Although the exact etiology of stuttering is unknown, both genetics and neurophysiology are thought to contribute. Although there are many treatments and speech therapy techniques available that may help increase fluency in some stutterers, there is essentially no "cure" for the disorder at present.