# Exploring the Age Effects on European Portuguese Vowel Production: An Ultrasound Study
## 1 Introduction
### Background  
#### 1.1.1 Aging Effects on the Articulatory Subsystem  
Noticeable anatomic and physiologic changes in the vocal tract or supralaryngeal system have been reported from young adulthood to old age [29]. During this period, facial bones continue to grow (3-5%) [29]. Additionally, a slight lowering of the larynx was observed, which is due to the atrophy of the head and neck muscles as well as the thinning of the intervertebral disks (more common in females), which leads to an increase of the length of the vocal tract [4; 5; 30; 31].  
In general, changes observed in the vocal tract include atrophy of the facial, the mastication, and the pharyngeal muscles, a decrease of the soft-palate volume, and loss of lip strength [3; 4; 5; 7; 29; 32; 33; 34]. The loss of elasticity and the thinning of the oral mucosa with the deterioration of attachments of the epithelium and connective tissue to bone are more apparent after age 70; however, these changes may happen earlier in life [29; 33]. Extensive degenerative changes occur in the temporomandibular joint (gradual reduction in size and reductions in blood supply), which controls the jaw movement during speech production [5; 7; 29]. In addition, a diminished accuracy of the lower lip and jaw when performing rapid movements has been reported with age [3; 32]. Furthermore, the shape of the oral cavity may change with the loss of teeth and the introduction of dentures [35].  
The salivary glands undergo acinar atrophy, ductal irregularities, and parenchymal replacement by fibrous and/or adipose tissue with aging, which causes a decline in salivary function [33; 34].  
Regarding the tongue, age-related muscular changes include muscle atrophy [36], decreased thickness of the lingual epithelium, reduced muscle fiber diameter, and fissuring of the tongue surface [29; 37]. Concerning the size of the tongue, contradictory findings have been reported in the literature [6]. While [PERSON] et al. [23] observed that the tongue of older people was reduced in thickness during rest, other studies have suggested that age-related changes in the tongue size are minimal to non-existent [6; 34; 37], which might be explained by the large increase of deposits of fatty tissue in the tongue to compensate the loss of muscle fibers [6; 36; 37]. On the other hand, [PERSON] [33] suggested an increase in tongue size because of two factors: muscle tone loss and the need to expand to fill the oral cavity space, as teeth are lost with aging.  
From a functional perspective, the older individuals have been reported to experience significant declines in tongue strength, although endurance remains stable throughout the major part of life [29; 38; 39]. [PERSON] et al. [40; 41] observed that the maximal tongue protrusion force decreases with age, while the tongue fatigability increases. In addition, drying of the tongue and of the oral cavity may lead to an increased resistance of tongue movement across the palate during speech movements [6].  
Furthermore, due to the loss of flexibility and muscular strength, aging can lead to deficits in speech motor control [1; 20; 42]. Previous studies about age effects in articulatory motor performance have demonstrated slower movements and reduced regularity in the rhythm of tongue movements, reduced tongue retraction, and smaller reductions in distance traveled by the tongue during fast speech rates with age [1; 6; 23; 37]. [PERSON] et al. [43] showed that the quality of the tongue muscles in healthy older speakers, assessed by the echo intensity of the tongue, is an indicator of tongue thickness at the middle and base of the tongue.  
All of these changes affect the vowel production [6; 7], as changes in vocal tract dimensions and in tongue motion may influence the resonance patterns in older speakers [7; 44].