Dysarthia refers to a group of disorders, in acquired or developmental form, which result from damage to the movement control systems of the central or peripheral nervous system. Aspects of speech production affected in dysarthia include respiration, phonation, articulation and prosody. Unlike apraxia, dysarthia involves weakness of muscles and incoordination. Causes of dysfluency difficult to discern. Organic theories relate dysfluency to some genetic or physical disposition which is triggered by environmental stress.
Psychoneurotic theories relate dysfluency to some aspect of the subject's personality.
Of course there is also the possibility that dysfluency is caused by a combination of organic and functional factors, thus it is difficult to decide between competing theories. Agnosia is a disorder, developmental or acquired, in which the ability to perceive sounds and objects is intact, while the ability to recognize them is impaired. Dyslexia refers to difficulty with reading, writing and spelling. It may be developmental or acquired. Conversely, the ability to pronounce regular words and non-words is unimpaired.