Course:PHYS341/2022/Project8

Background

The time graph of different sounds in English; note how they have the same fundamental frequency. In a tonal language, the fundamental frequency will differ to create pitch that distinguishes different sounds.

Throughout human evolution, communication has been an indispensable part of every civilization. Every culture has its own unique way of using the human voice to communicate ideas and emotions, notably through speech and singing. Similarly, body postures are also a means of expression during communication and our head and neck posture can fundamentally alter our voice. Our voice’s fundamental frequency (F0), defined as the lowest frequency component of a complex sound wave like human speech or music; it is also known as the "first harmonic" of a sound. In the context of human speech, it is defined as the rate of vibration of vocal folds in the context of speech [4]. Generally, F0 is 100-120 Hz in males, 200-240 Hz in females, and could reach up to 300 Hz in children [7]. F0 is an important of property that distinguishes lexical categories in tonal languages [4] and affects intelligibility of speech [2]; it also plays an important role in non-speech activities like singing.

Muscles involved

To increase the F0 and the pitch of one's sound, the vocalis muscles would contract and stiffen and vocal folds. The intrinsic laryngeal muscles cricothyroid (CT) and thyroarytenoid (TA) muscles can increase and decrease F0 [3]. It is thought that the activation of the CT and TA muscles changes the length or stiffness of the vocal fold cover layer, thereby increasing the F0 [3]. In this case, the CT muscle is mainly responsible for elongation of the vocal fold, but the function of the TA muscle is not entirely understood. According to a study by Chhetri et al. in 2014, the TA muscle is critical for moderating F0 and changing voice registers. In other words, activation of TA muscle allowed for an expanded F0 range. Working in conjunction with the CT muscle and lateral cricoarytenoid plus interarytenoid muscle complex, the TA muscle can contribute to the stiffness of the vocal fold or modify its shape, increasing F0 [3]. It is worth noting that this study was conducted in a canine model, hence the effects of each muscle on modulating F0 in humans may be different.

The muscles of the larynx

Extrinsic laryngeal muscles (suprahyoid, sternocleidomastoid, geniohyoid) can also modulate F0 by increasing muscle tension and elevating the larynx (Vilkman et al., 1996). The combined muscle activation of intrinsic and extrinsic laryngeal muscle activation, as well as increased airflow and glottal abduction will further raise F0 [8].

Other aspects that can influence the fundamental frequency

Since the activation of the CT and TA muscle will affect F0, then will posture of the head and neck complex change the activation levels of these muscles and modulate F0 as a result? The effect of neck posture on the activity of the intrinsic laryngeal muscles and voice quality have not been specifically investigated, but there are some researches that show that abnormal postures can affect the human voice. Angsuwarangsee & Morrison proposed that an abnormal head and neck posture can result in abnormal laryngeal postures. A combination of hyperlordosis of the cervical spine, head extension, and kyphotic hump in the upper thoracic spine can result in the poor laryngeal posture, making phonation more difficult and increases muscular tension around the larynx [1]. Chronic symptoms of the poor laryngeal posture may include persistent tensing of the laryngeal muscles [1]. Knowing how important laryngeal muscles are in controlling F0, increased resting tone and tension of them may significantly impact a person's voice characteristics. Although, the change in laryngeal muscles tension observed in this study is a result of chronic abnormal head and neck position, temporary change in position may not have the same effect.

A study by Kooijman et al. showed that postures that result in posterior weight bearing and hypertonicity of the sternocleidomastoid muscles will significantly increase vocal strain and decrease quality of voice. As well, hypertonicity of the geniohyoid and CT muscle, and anteroposition of the head as a result of abnormal laryngeal position also contributed to the increased strain [5]. It is clear that posture can significantly impact the quality and health of a person's voice. Therefore, those who frequently use their voices, such as lecturers or singers, may need to examine their posture to avoid vocal straining and chronic changes to laryngeal muscles.

The leftmost posture and rightmost posture were shown to increase vocal strain and disability in this study.

However, the effect of neck posture on the activity of the intrinsic laryngeal muscles and voice quality have not been specifically investigated. Therefore, it could be beneficial to examine the relationship between various pre-defined neck postures, intrinsic laryngeal muscles activity, and voice quality. This will shed light on the mechanisms of F0 modulation by the intrinsic laryngeal muscles in conjunction with the entire head and neck complex, rather than examining the CT and TA muscles as isolated units like in previous studies

Why this is important

F0 is a fundamental component of phonation and understanding the mechanisms that control it is critical as it influences the perception of all human sounds, including speaking, singing, or even speech recognition programs. But most importantly, advancing our understanding of the role of intrinsic laryngeal muscles and their collaboration with the head and neck complex in controlling F0 during human phonation can be useful for the study of speech and music alike. It is natural for humans to adopt different postures or neck muscle tension when performing vocal tasks, therefore, it would be important to learn about how these natural actions affect their voices, as well as what benefits or harms there these actions may bring.

References

Angsuwarangsee, T. and Morrison, M. (2002). Extrinsic laryngeal muscular tension in patients with voice disorders. Journal of Voice, 16(3), 333-343.
Brown, C.A. and Bacon, S.P. (2010). Fundamental frequency and speech intelligibility in background noise. Hearing research, 266(1-2), 52-59.'
Chhetri, D.K., Neubauer, J., Sofer, E. and Berry, D.A. (2014). Influence and interactions of laryngeal adductors and cricothyroid muscles on fundamental frequency and glottal posture control. The Journal of the Acoustical Society of America, 135(4), 2052-2064.
De Cheveigné, A. and Kawahara, H. (2002). YIN, a fundamental frequency estimator for speech and music. The Journal of the Acoustical Society of America, 111(4), 1917-1930.
Kooijman, P.G., De Jong, F.I.C.R.S., Oudes, M.J., Huinck, W., Van Acht, H. and Graamans, K. (2005). Muscular tension and body posture in relation to voice handicap and voice quality in teachers with persistent voice complaints. Folia phoniatrica et logopaedica, 57(3), 134-147.
Vilkman, E., Sonninen, A., Hurme, P. and Körkkö, P. (1996). External laryngeal frame function in voice production revisited: a review. Journal of Voice, 10(1), 78-92.
DPA Microphones. (2021, March 3). Facts about speech intelligibility: Human voice frequency range. DPA. Retrieved April 8, 2022, from https://www.dpamicrophones.com/mic-university/facts-about-speech-intelligibility
Hirano, M. (1974). Morphological structure of the vocal cord as a vibrator and its variations. Folia phoniatrica et logopaedica, 26(2), 89-94.