How science is giving voice to mummies such as Otzi the Iceman

Researchers recently managed to recreate the voice of 5,300-year-old Ötzi the iceman by recreating his vocal tract. The technology is promising and could be used to digitally produce the voices of other mummified remains. But how does it work and what else could it be used for?

When you make a vowel sound (aah, ee, oh, ooh and so on), three parts of your anatomy play important roles: your lungs, your larynx and the tube made from your throat and mouth. Your lungs provide the airflow that powers the sound. If the flow becomes too weak it will turn into a whisper instead.

Your larynx, or voice box, sits about midway between your lungs and your lips, just behind your Adam's apple. The part you can feel from the outside is the cartilage protecting and supporting the vocal folds (or vocal cords) inside. These are a pair of soft, lip-like structures that run from your Adam's apple to the back of your windpipe.

You can bring these folds firmly together across your windpipe to close it off completely – you do this when you cough or choke. You can also bring them across so they just touch, and if you do that and then breathe out they vibrate in much the same way your lips do if you blow a raspberry. These vibrating vocal folds are the source of sound for a vowel. If you say aah while you press your fingers gently either side of your Adam's apple you can feel the vibrations in your larynx.

Everyone's voice has a natural pitch based on the size of their larynx and in particular the length and thickness of their vocal folds. Your natural pitch is what comes out when your throat muscles are fairly relaxed and you don't try to speak too loudly. Women have shorter, thinner vocal folds than men and so they have generally a higher natural pitch.

If your windpipe ended just above the larynx then you would just be able to produce buzzing sounds. The lowest frequency in the buzzing sound is part of your natural pitch, but there is also energy at many higher frequencies included in that sound. It's the airway that shapes the buzz sound into a particular vowel.

We can think of this airway as a tube. You can change the length of that tube by protruding your lips, as you do when you say ooh, or by moving your tongue. When you say aah, your tongue rolls back out of your mouth and into your throat so the lower half of the tube is narrow and the upper half is wide, for example.

Every tube has a series of resonance frequencies that relates to its length and its cross-sectional area. These are the frequencies of sound that pass along the tube most easily and with least energy loss, so if we have a buzz sound generated at the larynx end of the tube, the sound at the lips' end will be the original buzz, but with the resonance frequencies of the tube sounding much louder than any other frequencies in the buzz.

When you listen to a vowel sound it's these resonance frequencies you are using to decide which vowel you are hearing. Changing the position of your tongue and lips changes the length and cross-section of the tube, which changes the resonances and ultimately the vowel you hear. Ötzi and his peers To know how Ötzi the Iceman sounded we need to know how long and how thick his vocal folds were – that tells us about the natural pitch of his voice. We also need to know how long his airway was and about the cross-sectional area to work out the resonance frequencies. His tongue and lips will have been preserved in one particular position which will only give us information about a single vowel sound. So if we are to work out how he sounded for other vowels we also need to know a bit about the size of his tongue and where it joined to his windpipe. Knowing this allows us to work out the other possible tube-shapes he could make and calculate their related resonances.

But how can you actually work all this out? It's pretty simple, all you really need is a CT scan, which uses X-rays to create detailed images of the inside of the body. This allows us to measure all these anatomical dimensions. We can then use that information to make a computer model to synthesise what his voice might have sounded like.

The first use of X-rays to explore mummified remains is thought to have been by Walter Konig in 1896, very soon after X-rays were first discovered. CT scans have been conducted on mummies for more than 40 years, with the popularity of the technique increasing rapidly over the last decade or so. However, the study of Ötzi the Iceman seems to be the first time the CT data has been used to synthesise a voice.

In a study of 137 mummies published in the Lancet in 2013, CT scans were used to show that, contrary to much current thinking, disease of the arteries was common in many pre-industrial populations. For speech, the CT scanning technique could similarly provide us with valuable information about the dimensions of the vocal system for any mummified body. And with enough different sets of scans we might be able to track trends in voice over time, such as changes in the typical natural frequency due to nutrition and body size.

One of the big open questions about speech is exactly when the ability to communicate in this way evolved, and there is quite a controversy about whether Neanderthals, for example, could speak. Sadly the CT scanning techniques can't help us with this as they rely on the preservation of soft tissue. The earliest hominid remains are fossilised which means only the bone structure has survived. The absence of lung, larynx, airway or tongue information in these fossils makes our ability to predict their capacity for speech very much less certain. At about 5,300-years-old Ötzi is the earliest European mummy in existence, but deliberately mummified bodies as old as 7,000 years have been found in South America. Spirit Cave Man, found in North America in 1940, has been dated at 9,000-years-old, so if CT scans were made, even older voices than Ötzi's could perhaps be heard one day.
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Reference:

Phys.org. 2016. “How science is giving voice to mummies such as Otzi the Iceman”. Phys.org. Posted: October 3, 2016. Available online: http://phys.org/news/2016-10-science-voice-mummies-otzi-iceman.html

Pronunciation of 's' sounds impacts perception of gender, CU-Boulder researcher finds

A person's style of speech — not just the pitch of his or her voice — may help determine whether the listener perceives the speaker to be male or female, according to a University of Colorado Boulder researcher who studied transgender people transitioning from female to male.

The way people pronounce their "s" sounds and the amount of resonance they use when speaking contributes to the perception of gender, according to Lal Zimman, whose findings are based on research he completed while earning his doctoral degree from CU-Boulder's linguistics department.

Zimman, who graduated in August, is presenting his research Jan. 5 at the annual meeting of the Linguistic Society of America in Boston.

"In the past, gender differences in the voice have been understood, primarily, as a biological difference," Zimman said. "I really wanted to look at the potential for other factors, other than how testosterone lowers the voice, to affect how a person's voice is perceived."

As part of the process of transitioning from female to male, participants in Zimman's study were treated with the hormone testosterone, which causes a number of physical changes including the lowering of a person's voice. Zimman was interested in whether the style of a person's speech had any impact on how low a voice needed to drop before it was perceived as male.

What he found was that a voice could have a higher pitch and still be perceived as male if the speaker pronounced "s" sounds in a lower frequency, which is achieved by moving the tongue farther away from the teeth.

"A high-frequency 's' has long been stereotypically associated with women's speech, as well as gay men's speech, yet there is no biological correlate to this association," said CU-Boulder linguistics and anthropology Associate Professor Kira Hall, who served as Zimman's doctoral adviser. "The project illustrates the socio-biological complexity of pitch: the designation of a voice as more masculine or more feminine is importantly influenced by other ideologically charged speech traits that are socially, not biologically, driven."

Vocal resonance also affected the perception of gender in Zimman's study. A deeper resonance — which can be thought of as a voice that seems to be emanating from the chest instead of from the head — is the result of both biology and practice. Resonance is lower for people whose larynx is deeper in their throats, but people learn to manipulate the position of their larynx when they're young, with male children pulling their larynxes down a little bit and female children pushing them up, Zimman said.

For his study, Zimman recorded the voices of 15 transgender men, all of whom live in the San Francisco Bay area. To determine the frequency of the "s" sounds each participant made, Zimman used software developed by fellow linguists. Then, to see how the "s" sounds affected perception, Zimman digitally manipulated the recording of each participant's voice, sliding the pitch from higher to lower, and asked a group of 10 listeners to identify the gender of the speaker. Using the recordings, Zimman was able to pinpoint how low each individual's voice had to drop before the majority of the group perceived the speaker to be male.
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References:

EurekAlert. 2013. “Pronunciation of 's' sounds impacts perception of gender, CU-Boulder researcher finds”. EurekAlert. Posted: January 4, 2013. Available online: http://www.eurekalert.org/pub_releases/2013-01/uoca-po010413.php

Speech lab: Unlocking the secrets of the human voice

It's an unusual performance. As James Wilkes reads aloud one of his poems, he slurs, stutters and stammers, struggling to get the words out. It's a far cry from his usually fluent readings of the material he knows so well. But today, James is taking part in an experiment at University College London's Speech Communication Lab. As he reads, his voice is played back to him through headphones just a fraction of a second later. And it is remarkably disruptive. He says: "It's a very, very odd experience. "It's like you are not saying words you have just said, so you are waiting for them to come. "The concentration involved is huge." Two cultures The writer has just taken up a poet-in-residence role at the Institute of Cognitive Neuroscience where the speech lab is based. He is hoping to get a creative insight into the science behind speech. "Everyone speaks, but it is something that is also really complex and strange," he explains. "The work they are doing at the lab is shedding some kind of light on that complexity and strangeness. And as a poet I really want to be part of that." The experiment that James has just taken part in is called Delayed Auditory Feedback (DAF), which is also known as speech jamming. Professor Sophie Scott, who heads the research group, says that it's a simple test that is helping to identify the mechanisms of speech. She explains: "What this is telling us is that when we speak, we make a noise, and if we fiddle around with that noise, it can make speech production difficult. "So it is telling us something interesting about how we use the sound of our own voice to guide speech output." Brain waves How we produce - and perceive - speech is the focus of research at the lab. Professor Scott says: "Speech is incredibly complex. "In fact, as a sound, speech or the human voice talking is comfortably the most complex sound you encounter on a day-to-day basis." She explains that just by hearing a few words, you start to build up an image of what a person might be like. "Our voices convey an awful lot of information about us, whether we want them to or not," she says. "If you couldn't see me, but hear me, you'd probably have a good guess at my sex, my age, where I come from, aspects of my mood and my socio-economic status - all of this is expressed in my voice. "But all sorts of other stuff too, like my aspirations and my hopes and what I'd like you to think of me. "I can guarantee to you that I sound different to talking to you here because I am trying to come across like a serious academic than if I was buying something a the market." The team is investigating the science behind speech in a variety of ways, from comparing recordings from around the world to see how communication varies across continents, to MRI scans that allow the researchers to identify which parts of the brain are activated as volunteers speak and listen to speech. And of course, as with any self-respecting cognitive neuroscience lab, behavioural experiments such as speech jamming feature too. In another test, Professor Scott asks James to read a text with her, out loud. It seems deceptively simple, but as they begin to read they have to synchronise everything: pauses, rhythm and even breathing to keep in time. Prof Scott explains that the simple experiment helps to reveal more about the complexities that exist in conversations. She says: "If you actually look at people together, they will start to coordinate their behaviour a lot to make conversation. "People will start to pronounce words in the same way, they'll coordinate their breathing. "Speech is actually a very, very complex social behaviour." James, who is spending several months with the speech team, is organising performances and events, such the Voices series of talks that will take place at UCL in April and May, to share what he is learning at the lab. But he also thinks it will have an impact on his own poetry. "[With speech jamming ] I found it changed the texture and the surface of what I was doing. I was slurring and stuttering, and those extra bits are really interesting to me as a poet," he explains. "It's something that is disruptive, it's unnecessary, excessive - and that to me is the material I want to work with." Prof Scott also thinks the poet's presence could have an impact on the way her team approaches their research. "You always learn something new from working with people who've got a different perspective," she says. "Psychologists tend to deal with speech as a disembodied language system, but the actual sounds of your language are incredibly important and have a lot to do with how you understand and interpret what people are saying to you. "And I think poets have a great deal of insight into that and a lot to say about the way we deal with the sounds people make around us." ________________ References: Morelle, Rebecca. 2012. "Speech lab: Unlocking the secrets of the human voice". BBC News. Posted: April 23, 2012. Available online: http://www.bbc.co.uk/news/science-environment-17790595