Science: We Hear What People Look Like

Can you hear what a person looks like? A growing body of research suggests so.

“The mere sound of a person’s voice contains important, embedded biological information,” says Susan Hughes, assistant professor of psychology at Albright College in Reading, Pa., who has researched vocal attractiveness and body symmetry. In her latest study, she finds a relationship between voice quality and another important biological marker: digit ratios. “The ratio of the second (index) finger to the fourth (ring) finger – the 2D:4D ratio – is an indirect measure of prenatal sex hormone exposure,” she says.

The development of digit formation is influenced by a surge of sex hormones during the first trimester of prenatal development – around the same time that vocal cords and the larynx are developed. “If the index finger is shorter in length than the ring finger, it’s a sign of greater prenatal testosterone,” she explains. “A longer index finger is a sign of greater prenatal estrogen exposure.”

“We found that women’s voices that were rated as more mature or as dominant had shorter index fingers relative to ring fingers,” she says,” This is a sign that they had greater prenatal testosterone than their female counterparts.”

“We weren’t able to find that correlation in our previous studies of vocal attractiveness,” she says. “It’s surprising; since voices tend to change during puberty, you would expect any prenatal effects to be washed away, but it turns out women, at least, still have them.”

The study, “The Sound of Symmetry Revisited: Subjective and Objective Analyses of Voice,” which appears in the June issue of the Journal of Nonverbal Behavior, is a follow-up to previous research she has conducted investigating vocal attractiveness and body symmetry.

Body symmetry – traits that are bilateral – are a sign of genetic fitness. “We are blue printed to develop perfectly symmetrical, but changes may occur during prenatal development that could affect our symmetry,” she says. “This physical trait is associated with increased genetic, physical and mental health and is an important factor in mate selection.”

“In my previous work we found that individuals with voices rated as attractive had bilateral body traits that were more symmetrical,” she says. “Here we found that other voice ratings – for approachability, sexiness, warmth or intelligence – were also related to body symmetry.”

Hughes, along with co-authors Dr. Gordon Gallup at the State University of New York at Albany, and Dr. Matthew Pastizzo at the State University of New York at Geneseo, asked volunteers to listen to recorded voices and rate them on nine different traits shown to be important in mate selection: approachability, dominance, healthiness, honesty, intelligence, likelihood to get dates, maturity, sexiness and warmth.

“We then tried to look at the elements of voice to find features about them that could identify what element made up an ‘attractive’ voice or an ‘approachable’ voice, but couldn’t break it down into individual components,” she says.

This was done in a process called spectrogram analysis, which measured voice samples for pitch, pitch range, number of voice breaks, intensity and duration of sample. Voices were also measured for “jitter” and “shimmer” – characters that give a voice a hoarse quality.

“Voices are a complex combination of several qualities,” she says. “It may be the unique combination of features together that conveys information that potential mates can use to make assessments regarding mate quality and fitness.”

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