Transcript vocal folds
Phonation + Vocal Fold Physiology Feburary 6, 2013 Average Everydayness • Production exercise comments and grades were e-mailed shortly before class; • I’m sending the second one out tonight. • Will be due next Wednesday… • Today: • The Wonderful World of the Larynx! • But first: a completely random linguistic detour... The Kiki/Bouba Experiment • Originally devised by psychologist Wolfgang Köhler in 1927. • Updated and replicated in 2001. • Look at these two figures: • Which one is bouba and which one is kiki? • ~95% of both English and Tamil speakers thought the shape on the left was “kiki”, the one the right “bouba” Where Were We? • Air squeezed out of the lungs travels up the bronchi... • Through the trachea (windpipe) • To a complicated structure called the larynx. • ...where phonation happens. The Larynx • The larynx is a complex structure consisting of muscles, ligaments and three primary cartilages. 1. The Cricoid Cartilage • The cricoid cartilage sits on top of the trachea • from Greek krikos “ring” • It has “facets” which connect it to the thyroid and arytenoid cartilages. cricoid cartilage 2. The Thyroid Cartilage • The thyroid cartilage sits on top of the cricoid cartilage. • from the Greek thyreos “shield” • The thyroid cartilage has horns! • Both lower (inferior) and upper (superior) horns • The lower horns connect with the cricoid cartilage at the cricoid’s lower facet. • The upper horns connect to the hyoid bone. Thyroid Graphic thyroid cartilage cricoid cartilage Thyroid Angles • The two broad, flat front plates of the thyroid--the laminae--meet at the thyroid angle. • The actual angle of the thyroid angle is more obtuse in women. • ...so the “Adam’s Apple” juts out more in men. 3. The Arytenoid Cartilages • There are two arytenoid cartilages. • from Greek arytaina, “ladle” • They are small and pointy, and sit on top of the back side, or lamina, of the cricoid cartilage. arytenoid cartilages cricoid cartilage The Vocal Folds • These three cartilages are connected by a variety of muscles and ligaments. • The most important of these are the vocal folds. • They live at the very top of the trachea, in between the cricoid and thyroid cartilages. • The vocal folds are a combination of: • The vocalis muscle • The vocal ligament • The vocal folds are enclosed in a membrane called the conus elasticus. Vocal Fold View #1 • Just above the true vocal folds are the “false” (!) vocal folds, or ventricular folds. • The space between the vocal folds is the glottis. Vocal Fold View #2 • The vocal ligaments attach in the front to the thyroid cartilage. • ...and in the back to the arytenoid cartilages. • The glottis consists of: • the ligamental glottis • the cartilaginous glottis Things Start to Happen • Note that the arytenoid cartilages can be moved with respect to the cricoid cartilage in two ways. #1: rocking #2: sliding The Upshot • The arytenoids can thus be brought together towards the midline of the body. • Or brought forwards, towards the front of the thyroid. • The rocking motion thus abducts or adducts the glottis. • The sliding motion shortens or lengthens the vocal folds. • Check out the arytenoids in action. • When the vocal folds are abducted: • air passes through the glottis unimpeded and voicelessness results. • The posterior cricoarytenoid muscles are primarily responsible for separating the arytenoid cartilages. • Voicing may occur when the vocal folds are adducted and air is flowing up through the trachea from the lungs. • Two muscles are primarily responsible for adducting the vocal folds. • The first is the lateral crico-arytenoid muscle. • Note that the lateral cricoarytenoid muscles only adduct the ligamental glottis. • The transverse arytenoid muscles pull together the arytenoid cartilages themselves. • Thereby closing the cartilaginous glottis. The Consequences • The combined forces drawing the vocal folds towards each other produce adductive tension in the glottis. • Adductive tension is increased by: • lateral cricoarytenoid muscles • transverse arytenoid muscles • Adductive tension is decreased by: • posterior cricoarytenoid muscles • Adduction vs. abduction determines whether or not voicing will occur. • But we can do more than just adduce or abduce the vocal folds... Controlling F0 • Question: why do women have a higher F0 than men? • A: Shorter vocal folds open and close more quickly. • In men: • Ligamental glottis 15.5 mm • Cartilaginous glottis 7.5 mm • Total glottis length 23 mm • In women: • Ligamental glottis 11.5 mm • Cartilaginous glottis 5.5 mm • Total glottis length 17 mm Factor Two • F0 also depends on the longitudinal tension in the vocal folds. • I.e., tension along their length, between the thyroid and arytenoid cartilages. • Higher tension = higher F0 • Lower tension = lower F0 • Q: How can we change longitudinal tension in the larynx? • A: We can rotate the thyroid cartilage up and down on its connection with the cricoid cartilage. • ...like the visor of a knight’s helmet. • This either stretches or relaxes the vocal folds. Contradictory? • No, just complicated. Note: • Lengthening (stretching) the folds results in higher tension • ...which results in higher F0 • Shortening the folds results in less tension • ...which results in lower F0 • “Higher” and “lower” F0 have to be understood relative to the speaker’s normal F0 range. • still lower for men • still higher for women For the Record • Contraction of the cricothyroid muscle pulls down the thyroid cartilage. • Interestingly: researchers often study the activity of this muscle using EMG. Fun Stuff (= tracheotomy) Peter Ladefoged: “To record the pressure of the air associated with stressed as opposed to unstressed syllables we need to record the pressure below the vocal folds. A true recording of the subglottal pressure can be made only by making a tracheal puncture.This is a procedure that must be performed by a physician. A local anesthetic is applied both externally and inside the trachea by means of a fine needle. A larger needle with an internal diameter of 2 mm can then be inserted between the rings of the trachea as shown in figure 3.3” Figure 3.3 “As you can see from my face it is not at all painful. But it is not a procedure that can be carried out in fieldwork situations.” For the Record, part 2 • Longitudinal tension can also be reduced by the thyroarytenoid muscles. • Which connect the thyroid to the arytenoid cartilages. • These muscles are inaccessible to EMG vocal folds Check it out! • Let’s look at some pitch shifting laryngoscopy videos.