Speech production is the crux of human communication both in typically and atypically developing populations. Individuals with Down Syndrome (DS) show many speech production deficits, which prevent them from achieving effective communication. This paper seeks to describe the major factors that affect speech in DS by reviewing current medical research and pertaining specific factors to certain phonological errors. Evidence regarding the anatomy, motor skills, and cognition of affected individuals highlights that macroglossia, dysarthria, and apraxia should be critically taken into consideration when examining the etiology of impaired speech production.
Atypical populations are characterized by various types of disabilities and disorders (genetic, congenital, neurodevelopmental, acquired, and neurodegenerative). Down Syndrome (DS) is an example of a genetic disorder that is caused by an abnormality of chromosome 21 and is considered to be the leading cause of intellectual disability . Apart from the cognitive impairments of populations with DS, there are language-specific deficits relating to syntax, semantics, pragmatics, phonology, and vocabulary acquisition. When phonology is put under the microscope, we realize that we need to shed more light on the production of speech and, more specifically, illuminate the factors that affect it. It seems that the most common variables influencing speech production fall under three categories: anatomy, motor skills, and cognition.
One of the major factors hindering typical speech development in individuals with DS is related to their tongue. In order to produce complex sounds like consonants, the tongue is required to move around the oral cavity and be placed onto or near specific regions, such as the alveolar ridge, the teeth, or the palate. Since deep grooves have been observed to be prevalent both on the tongue and on the lips, the so-called fissured tongue and lip fissures, which are two of the most common features in individuals with DS, play a role in misarticulation .
Macroglossia (macro = large, glossa = tongue) is also a medical term utilized to indicate the enlarged tongue of these individuals . However, recent studies show that they have relative macroglossia, namely a relatively large tongue . Their tongues appear larger when compared to the size of their oral cavity, where they have a high-arched and narrow palate (see Figure 1). This is why they fail to accurately articulate palatal and alveolar consonants . Moreover, this anatomical distortion of the hard palate occurs after the first year of life, a fact which is very medically relevant overall .
Another significant finding that influences the voice of children with DS is the fact that these individuals face problems with their airways, such as laryngo-tracheo-bronchial pathology, which is related to the hypothesis that DS is associated with a characteristic dysphonia . Dysphonia affects the voice of these individuals, causing them to have “[l]ow vocal pitch and a hoarse, harsh, or raucous voice” . Taking into account the aforementioned factors, namely relative macroglossia, the fissured tongue, the lip fissures, and the problems with the airways, it becomes evident that congenital abnormalities have a significant impact on defective articulation of speech.
Coordination motor skills play a pivotal role in properly combining sounds in order to articulate words and sentences. Diadochokinetic assessment is generally used to determine whether a person who has DS is unable to properly produce speech due to delayed neuromotor maturation . More specifically, oral-diadochokinetic (oral-DDK) rates tasks examine the speech motor skills of these individuals in terms of how fast they are able to repeat both monosyllables and sequences of different syllables . For instance, patients are required to repeat the syllables /ka/ and /ta/ on their own and then the sequence of the syllables /pa.ta.ka/. These tasks provide information about their motor skills as well as their accuracy in syllable production altogether.
Research that explores which specific sounds are mostly misarticulated has shown that vowels belonging to the close-open region (see Figure 2) are the ones that are most affected . As far as consonants are concerned, the most common misarticulations are found in the alveolar ridge (/r/ and /s/), the velum region (/k/), and the labiodental region (/v/) . When these phonological errors emerge from a motor speech disorder, otherwise described as dysarthria, scientists argue that it may be correlated with the generalized hypotonia found in DS, a condition characterized by decreased muscle tone . Others argue that these errors should be further examined from a neuropsychological perspective.
Many studies conducted have been unraveling the neuropsychological profile of DS. Long-term, short-term, and working memory have not been investigated in the early years of childhood, but only in later development, where weaknesses have been reported in social communication and learning skills . Speech articulation and perception abilities are influenced by the verbal (phonological) short-term memory, i.e., individuals with DS fail at speech production and segmentation because they have indistinct and poor phonological representations . Phonological representations refer to the sounds that are stored in the phonological-mental lexicon. When individuals with DS have to process information that is not already well acquired, then it is possible that they will not be able to produce it properly.
Apart from facing issues with their mental representations, phonological planning, the cognitive ability to sequence the proper phonemes in order to utter a word, is a major factor that needs to be critically considered . This disorder of motor programming is defined as apraxia, which in contrast to the aforementioned disorder of speech neuromuscular control (dysarthria), is pertinent to the cognitive skills required for speech production . In particular, both the memory processes that “store and retrieve [phonological] representations” and the transcoding processes that “plan and program the representations for the motoric gestures of manifest speech” are paramount concerns that hinder effective articulation.
Speech perception and production constitute the cornerstones in infants’ typical and effective language acquisition. When investigating the major factors that result in defective speech production in Down Syndrome, it becomes more and more challenging for researchers and clinicians to identify the reasons why speech is affected. It becomes incumbent on speech-language therapists to holistically examine the populations with DS by taking into consideration their anatomy, their motor skills, and their cognitive development.
I am a senior undergraduate student at Aristotle University of Thessaloniki (AUTH) and I study English Language and Literature. I teach English as a foreign langauge and I am a volunteer translator at TED. The field of Linguistics and more specifically Psycho- and Neurolinguistics have drawn my attention during my studies. When language is examined from different scientific perspectives, namely cognitive, social and neural, the evidence that arises sheds light on significant and hidden spots in the uncharted territories of psychology, sociology and neurology.