Unintelligible speech is a descriptive term used subjectively by the listener. It can be due to a few minor consonant or vowel errors, oral-structural differences, oral-motor weakness, dysarthria or apraxia of speech.
However, another casual factor to unintelligible speech, which even many professionals miss, is that of the faulty perception of language. Children who have difficulty processing and comprehending spoken language, particularly children who exhibit autism spectrum disorders, may exhibit jargon (sometime called “gibberish,” or unintelligible speech).
It is important to uncover whether a child has an unusual capacity to memorize dialogue, which doesn’t necessarily hold any meaning for them and are reiterating it the way they perceive it, without attaching meaning. In this case, the more emphasis there is upon improving processing and comprehension skills, the more improvement will be seen in increased intelligibility. Whereas, unintelligible speech rooted in the fine-motor coordination aspect of talking would require motor-speech or verbal motor work.
Children may have both perceptual and motor-speech difficulties. If there are any questions regarding whether the child comprehends spoken language, attention should be given to comprehension and not necessarily motor-speech output.