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Advances in Physiological Measures in Speech Research

Understanding Childhood Apraxia of Speech

Christopher Moore, Ph.D.

One of the most difficult challenges in understanding Children’s Apraxia of Speech (CAS) is identifying its primary characteristics. It may be that there are core features that can be observed at a number of levels in the speech production chain, including the behavioral level (what a listener might describe about a child’s speech), the acoustic level (what we can analyze instrumentally from speech sounds), the programming level (what we can infer about how the speech process is controlled by the nervous system), and the physiologic level (what we can observe as the movements by the speech structures, including the respiratory system, the larynx, and the articulators). Of course these levels all interact, but observations of one may reveal characteristics not seen in others. Descriptions of CAS have historically reflected the technologies available. As is typical for emerging diagnostic categories, anecdotal description has expanded to incorporate more formalized description (e.g., relying on standardized tests), and more elaborate instrumental methods. The scientific standard for acceptable clinical evidence in speech-language pathology continues to mature from speculation and limited observations of one or several children, to studies of larger populations using rigorous experimental methods.

Striking advances in the measurement of speech physiology have arisen largely from the rapidly expanding power of computation. Our capacity to analyze speech digitally, to track movement using digital video, and to analyze long periods of behavior have surged as the cost and availability of digital methods have improved. I only wish that I could adapt (Gordon) Moore’s Law, which states that the maximum possible number of transistors on a computer chip will double every two years, to (Chris) Moore’s Law, which would state that our understanding of speech motor control would double every two years. Unfortunately, our questions remain largely the same, while our tools become increasingly powerful:

  • How do the speech movements of a child with impaired speech differ from those of a child whose speech is developing more typically?
  • Are there differences in strength, breathing patterns, voice use, or sensation?
  • How do we measure muscle tone or sensorimotor integration?
  • How can we measure treatment efficacy objectively?
  • Does treatment in one area translate to improvement in a very different area (e.g., non-speech drill as a way to improve speech)?
  • Are reflexes a relevant part of speech production?

What is most encouraging now is that it is possible to evaluate large groups (e.g., in the hundreds) of children, whereas until relatively recently it had only been possible to study a few subjects at a time. Scientific limits because of small samples or limited observational methods are no longer accepted. This advancement is especially important in CAS, as the differences among children with CAS greatly outnumber the similarities. Discovery of the common features of CAS will enhance our understanding of what CAS is, what the most appropriate treatment approaches are, and what prognoses can be anticipated.