4 Diagnosing Dysarthria in Adults responsible for phonation, articulation, and prosody, including intonation, rhythm, and speech rate (tempo). Speech planning has to be seen as distinct from execution, and this distinction is crucial in accounting for speech disorders of the dysarthria type. Dysarthria is defined as a disorder of speech production resulting from organic causes. Speech planning, i.e. selecting words or constructing sentences, is therefore not affected in dysarthria; nor are language comprehension, vocabulary resources, or the functioning of the semantic memory (unless dysarthria is accompanied by other disorders, such as aphasia or dementia, which can cause additional problems with comprehension, attention, speech planning, and production). Rather, the pathological symptoms characteristic of dysarthria manifest themselves in speech motor production, specifically including impaired articulation, problems with producing nasal/oral features of speech sounds, problems with rendering prosodic features of an utterance, such as intonation, stress, speech rate (which can become accelerated, decelerated or varied), shortened phonation time (i.e. voicing production), possible breathing disorders (such as shortened breath or loud inspiration/expiration), or various voice disorders, such as diminished intensity or qualitative disorders, including hoarseness, lack of sonority, flat sound, etc. Before I discuss the dysarthria-related pathological changes in speech production in detail, however, let us first review the most essential aspects of speech production in general. 1.2. VOCALIZATION AND PRODUCTION OF SPEECH SOUNDS Speech production involves five independent physiological processes, i.e. articulation, breathing, phonation, resonance, and prosody. The physiological actions underlying speech production therefore involve collaboration among a number of different organs. Articulation engages the tongue, lips, lower jaw, palate, larynx, and respiratory muscles. Phonation also usually requires an appropriate airflow, proceeding from the lungs, bronchial tubes, and trachea, to the larynx, which amplifies the voice’s fundamental frequency, and the pharynx, nasal and oral cavities—all responsible for the timbre of the voice and for producing specific speech sounds (Minczakiewicz 1990, Ichikawa & Kageyama 1991). Breathing itself is the work of the lungs, thoracic cage, diaphragm, and abdominal muscles. For breathing to take place, central control has to be exercised over the respiratory muscles. The respiratory system carries the
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