# Exploring the Age Effects on European Portuguese Vowel Production: An Ultrasound Study
## 1 Introduction  
Aging involves changes at physiological, cognitive, psychological, and social levels. Age impacts the human body in a plethora of ways, entailing changes to the musculoskeletal, the cardiovascular, the respiratory, and the central nervous systems [1], and the speech production system is no exception [2]. Thus, the aging process causes specific alterations in the speech organs (e.g., decreased lung capacity, weakening of respiratory muscles and atrophy of facial, mastication, and pharyngeal muscles) [3; 4; 5], and all these changes are expected to play an important role in speech production. Although limited research has been carried out specifically to ascertain what changes occur in the supralaryngeal structures (particularly in the tongue) with aging, modifications in these structures could considerably affect the speech production [6].  
Although age-related variations on the acoustic properties of speech have been extensively investigated over the years [4; 5; 7], its underlying articulatory adjustments have not been well understood. Due to the fact that the vowel formant values are suited toarticulatory interpretations (i.e., formant frequencies reflect the length and configuration of the vocal tract [8; 9; 10; 11; 12]), formant measurements have been used in the study of speech production. Thus, the first (F1) and second (F2) formant frequencies reflect primarily tongue position and lips rounding [13]. As for age-related changes on vowel formant frequencies (mostly F1 and F2), the results across studies are highly inconsistent [4; 5; 11; 14]. In addition, European Portuguese (EP) vowels presented a different pattern of formant frequencies variation with age and gender [15; 16; 17]. [PERSON] et al. [16; 18] observed that vowel formants tend to decrease mainly in females and to centralize in males with aging, and these changes might be related to specific articulatory adjustments of the older speakers during speech.  
Unlike acoustic studies, for articulatory studies, there are only a few that examine the effects of aging on tongue position and strength during speech production [1; 19; 20; 21; 22]. Ultrasound (US) tongue imaging synchronized with audio can be used to investigate the physiological differences between old and young adult speech [19; 23], as approached in our previous work with four female speakers [22]. Nonetheless, US tongue image processing and the inter-speaker comparison are challenging [22]. Targeting the main limitations of our previous study, the main purpose of this work is to perform a larger study of the age-related articulatory differences in EP vowels with US imaging and to investigate normalization procedures. Additionally, since there is a paucity of literature on EP oral vowels production, and the available data were collected mainly for acoustic studies [15; 16; 24; 25] or for articulatory studies of nasal vowels [26; 27; 28], this study also provides valuable insights for the accurate articulatory description of EP oral vowels with US.  
The data obtained will allow infering preliminary results of the age effect on EP vowel production, which is essential for the development of automatic speech recognition (ASR) systems suitable for older speech and for clinical assessment and treatment of speech disorders.