Mutism, autism and dysphasia are among the severe impairments of communication abilities. Specific impairment of voice production may be due to laryngeal deficiency, artificial larynx, laryngeal palsy or from deficiencies in other speech organs. The indistinct speech that results may be characterized by drawling, mumbling, slurring, etc. Impairments of voice function include absent or irregular voice modulation, pitch, intonation or volume; and harsh or other deficient qualities. Impaired speech forms includes stuttering, stammering, and similar disorders.
As is generally known, speech disorders may have psychological causes. Thus, just as there are normal behavioural and speech ranges, atypical speech may be viewed as a disorder. In this class fall excessively copious and rapid speech, unusual speech patterning, phonation and resonation. This class of speech disorders may also include distorted grammar, lack of logical connection, sudden irrelevancies, interminable digressions, and answering off the point. Non-social speech, in this category, is talking, muttering or whispering out loud; and impaired conversation is exhibited by simultaneous talking or talking out of turn. Impaired speech content includes idiosyncratic uses of phrases and terms, neologisms, excessively recurrent punning, rhyming, joking or impaired humour, singing and irrelevant location.