Articulation disorders, also known as phonetic disorders, affect more children and adults than most people realize. In fact, only about 10 percent of the general population exhibits perfectly “normal” speech in terms of being completely free of tonal imperfections or articulation and phonological disorders. In children, articulation disorders are most frequently associated with neurological disorders due to birth complications or genetically inherited medical conditions that can affect speech, such as neurofibromatosis and cystic fibrosis. Adult speech, on the other hand, most commonly becomes altered later in life due to a stroke, brain trauma, or the onset of dementia. However, articulation disorders can also appear in both adults and children without any specific known cause.
The most common classification of articulation disorders is referred to simply as voice disorders. Although voice disorders include a greater range of problems than articulation, some of these difficulties can impact speech quality as a secondary consequence. For instance, abnormal voice quality due to injury, disease, or surgical removal of the larynx will likely produce articulation disorders in addition to difficulties regulating speech volume, tone, and pitch.
Other general speech disorders that can negatively affect articulation include stuttering and cluttering, which are characterized by the involuntary repetition of words or a disordered rhythm of speech, respectively. These factors are significant since a large percentage of people who exhibit such disorders also display articulation disorders. In addition, those who have receptive language difficulties are likely to adopt incorrect phonetic patterns due to being unable to adequately process and learn sounds. This may be due to a hearing impairment, or due to an inability to distinguish differences between particular sounds. For example, children with articulation disorders frequently have trouble with certain consonants and may pronounce them all the same in way in a linguistic event known as a phoneme collapse.
Similarly, articulation disorders may stem from impaired comprehension of speech due to some form of injury to the brain, such as a stroke. In addition to speech recognition being affected in such cases, the inability to produce speech often occurs as well. This type of acquired articulation disorder is known as aphasia. However, if speech becomes labored specifically due to difficulty swallowing as the result of a stroke or neurological disorder, then the condition is referred to as dysphagia.
Dysarthria is another speech disorder that may also develop after a stroke or brain injury. However, dysarthria produces articulation disorders due to weakness or paralysis of facial muscles. Dysarthria also occurs in those with progressive neurological disorders, such as Parkinson’s disease, cerebral palsy, or amyotrophic lateral sclerosis, or Lou Gehrig's disease.
While articulation disorders may occur due to a variety of causes, scientists are making steady progress in identifying specific genetic factors. In fact, the Journal of Neurodevelopmental Disorders recently published the results of a study that was part of a 20-year program designed to investigate genetic causes of speech and language disorders. The study confirmed previous findings that such disorders are linked to gene KIAA0319 of Chromosome 6.