Childhood Apraxia of Speech (CAS) is a motor speech disorder that first becomes apparent as a young child is learning speech. For reasons not yet fully understood, children with apraxia of speech have great difficulty planning and producing the precise, highly refined and specific series of movements of the tongue, lips, jaw and palate that are necessary for intelligible speech. Apraxia of speech is sometimes called verbal apraxia, developmental apraxia of speech, or verbal dyspraxia. No matter what name is used, the most important concept is the root word “praxis.” Praxis means planned movement. To some degree or another, a child with the diagnosis of apraxia of speech has difficulty programming and planning speech movements. Apraxia of speech is a specific speech disorder. This difficulty in planning speech movements is the hallmark or “signature” of childhood apraxia of speech.
The challenge and difficulty that children with apraxia have in creating speech can seem very perplexing to parents, especially when they observe the skill of learning to speak developing seemingly without effort in other children.
How Does Speech “Happen”?
The act of speech begins with an intention to communicate. Next, an idea forms, outlining what the speaker wants to say. The words for the desired message are put in the correct order, using the correct grammar. Each word contains a specific sequence of sounds (also called phonemes) and syllables that must be correctly ordered together. All of this information is translated from an idea and information about order of sounds and syllables into a series of highly coordinated motor movements of the lips, tongue, jaw, and soft palate.
The brain must tell the muscles of these “articulators” the exact order and timing of movements so that the words in the message are properly pronounced. Finally, the muscles themselves must work properly with enough strength and muscle tone to perform the movements needed for speech. Amazingly, all of this happens in the blink of an eye.
When speech is developing in a normal way, children make word attempts and get feedback from people around them and from their own internal sensory systems regarding how “well” the words they produced matched the ones that they wanted to produce. Children use this information the next time they attempt the words and essentially are able to “learn from experience.” Usually once syllables and words are spoken repeatedly, the speech motor act becomes automatic and less effortful. The child doesn’t have to think about how to say the word or phrase they want to say. At this point, speech motor plans and programs are stored in the brain and can be quickly accessed and put together effortlessly when they are needed. Children with apraxia of speech have the most difficulty in this aspect of speech. It is believed that children with CAS may not be able to form or reliably access speech motor plans and programs or that these plans and programs are faulty for some reason. Unlike children developing typical speech, speech motor plans and programs for children with CAS fail to become automatic and easily accessed when they wish to speak.
Recent research also suggests that, to some degree or another, the sensory feedback loops needed for learning and acquiring accurate speech may not work well in children with apraxia of speech. There are several forms of feedback children use to learn speech and the complex series of movements underlying it. First, children use auditory information (through their hearing system) to judge whether their word attempt was correct. Researchers believe that the child’s speech processing system “couples” (or ties together) an auditory event – what they hear themselves say – with the movements of the oral structures needed to produce an utterance. Secondly, sensory feedback called proprioception is used so that the child knows where speech structures like lips, jaw, tongue, palate are physically located and how they relate spatially to one another during speech movement. So, for example, during speech attempts the child may not be aware of where their tongue is within the oral cavity or how its position relates to other structures like the lips. Sensory feedback is especially important during the learning of motor plans such as in early speech learning or speech acquisition. If these two feedback mechanisms are not working properly, speech intelligibility is affected.
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