Hysterical aphonia is a functional disorder. It is not organic laryngeal paralysis. Patient with hysterical aphonia can not adduct the vocal cords when attempting to speak. Psychogenic condition subh as emotional may cause aphonia. The patient hopes to be relieved of an unpleasant duty through loss of his voice.  We can take an example ; if the amateur speaker is unable to prepare his topic,he will become aphonia. This condition make he able to cancel his speech without embarrasment.

What is mental retardation? It is the failure to develop normal mental capacities. We can use test of intelligence such as the Wechsler Preshool, the Standfor- Binet IQ and Primary Scale of Intellgence-Revised to classify mental retardation. Normal IQ is 100 and have standard deviation of 15.