For Diagnosing Motor Speech Disorders, Perception is Reality
Speech-language pathologists work with patients having a wide variety of disorders that arise from complications in different structures of the brain and/or muscles. For example, a person can have an articulation disorder due to an enlarged tongue or shortened frenulum. Persons can also have disorders of the language structures of their brain affecting their comprehension or expression of a spoken, written, or signed message. These types of disorders are often measured by different validated tests to show areas of deficits on a standardized scale. However, for neurological motor speech disorders (MSDs), the most common and reliable source of assessment is the highly trained ear of the speech-language pathologist (SLP). The perceptual method of evaluating motor speech disorders relies primarily on auditory discrimination of the patient’s speech output. Thanks to the work of Darley, Aronson, and Brown, the auditory-perceptual method of assessment has been shown to be effective in discriminating between the various types of dysarthria and understanding their differing features according to the site of lesion. “They [perceptual methods] are the gold standard for clinical diagnosis, judgments of severity, many decisions about management, and the assessment of meaningful temporal change” (Duffy, 2013).
As part of training, SLPs must learn to identify perceptual aspects of speech motor control that are indicate of underlying neuropathology. Using a well-trained ear and clinical expertise, the SLP can assess the functioning of various systems that contribute to speech production, including the respiratory, phonatory, articulatory, and velopharyngeal systems. Often times, dysarthria or apraxia of speech “announce” the onset of degenerative diseases such as progressive supranuclear palsy or corticobasal syndrome. As such, SLPs oftentimes play a critical role in determining differential diagnoses for diseases that cause the motor speech disorder.
Though perceptual methods are of most importance, instrumental methods have played a vital role in understanding and complementing the use of perceptual qualities in diagnosing MSDs. There are essentially three types of instrumental methods, which are as follows: acoustic, physiologic and visual imaging. Acoustic methods measure the frequency, intensity and temporal components of a speech signal. This provides tangible data to support the clinician’s perception. Current research exists that could lead to an increase in acoustic methods used more widely. Acoustic technology has also become more affordable and accessible. Physiologic methods focus on the sources that generate sound including muscle contractions, movements of speech structures, temporal parameters and temporal relationships. These methods help link pathophysiology with perceptual aspects of motor speech disorders. They also help determine where the breakdown in the hierarchy of speech is occurring. One example would be deciding if the issue at hand is a motor planning versus motor programming issue. Determining this using solely perceptual aspects is extremely difficult. Visual imaging methods are primarily used to view the upper aerodigestive tract during speech. Some common examples of visual imaging methods are videofluoroscopy, nasoendoscopy and laryngoscopy. These also aid in evaluating swallowing disorders, or dysphagia, which is seen in many of the patients with a MSD.
In summary, an SLP with highly trained perceptual listening skills is essentially irreplaceable. In guiding diagnosis and management of MSDs, the use of perceptual evaluation is not a matter of clinician’s preference, but rather of need. Despite technological advancements, acoustic, physiologic, and imaging measures remain adjunctive tools to the perceptual speech evaluation. As summarized by UF Professor Emeritus Dr. J. Rosenbek: “the ear may be the final arbiter in detecting apraxia of speech and dysarthria” (Duffy, 2013).
Duffy, J. (2008, November 1). Motor Speech Disorders and the Diagnosis of Neurologic Disease. Retrieved September 15, 2015, from http://leader.pubs.asha.org/article.aspx?articleid=2288080
Duffy, J. (2013). Defining, Understanding, and Categorizing Motor Speech Disorders. In Motor Speech Disorders: Substrates, Differential Diagnosis, and Management (Third ed., pp. 7-9). St. Louis, Missouri: Elsevier Mosby.