October 17, 2013
Elephants And Humans Share Similar, Yet Distinct, Vocal Abilities
Michael Harper for redOrbit.com - Your Universe Online
With the natural passing of an African elephant in Berlin Tierpark Zoo in 2010, the researchers were able to recover the larynx and bring it into the lab for studying. In their paper released last year the researchers explained how similar an elephant's vocal system is to those used by humans.
Lead researcher Christian Herbst didn’t stop studying the larynx once the paper was published, however, and now says while similar, there are key differences between the way an elephant makes sounds and the way humans make sounds. Herbst’s new research can be found in The Journal of Experimental Biology.
Just like a human’s, the elephant’s larynx produces sound when air is passed through two vocal folds. Herbst and his team were able to recreate sound in the larynx by holding it in the ready position and blowing warm, humid air through these folds. Yet while similar, Herbst now says the folds in the elephant larynx are situated at a very acute angle in relation to the air stream, blocking two-fifths of the folds from the stream of air. Furthermore, and understandably so, an elephant’s vocal cords are exponentially longer and thicker than those found in a human’s larynx.
Herbst observed these differences as he conducted CT-scans on both the recovered larynx and those found in human volunteers. Next he filmed the way the elephant’s vocal cords moved as the humid air was blown through them. Just as it was observed before, Herbst says the vocal cords vibrated passively with the airflow. These vibrations are capable of producing sound in what’s known as the infrasonic range, anywhere below 20Hz. Unlike a human’s voice, however, the elephant’s cords don’t begin to produce a sound until later in the process.
Herbst explains the difference this way: “In humans, most of the sound is created when the vocal folds clap together, but we observed that in the elephant, interestingly, most of the sound was generated when the vocal folds separated."
In another observed difference, the vocal fold vibrations in the elephant larynx varied from those in humans. The human vocal folds produces two transverse traveling waves when air is flowing through them. The two oppositely traveling waves are superimposed on one another and create a standing wave. In elephants, however, only one wave was observed when one vocal fold was held taut. This single wave moved back and forth along the folds.
“Looking at transverse traveling waves offers us an alternative way to study and appreciate the physical phenomenon that is going on in voice production,” says Herbst.”
By understanding how elephants make sound, Herbst says researchers may one day be able to better understand the ways humans make sound and how capable our own vocal folds can be in creating different sounds.