“Her face was sad and lovely with bright things in it, bright eyes and a bright passionate mouth, but there was an excitement in her voice that men who had cared for her found difficult to forget: a singing compulsion, a whispered “Listen,” a promise that she had done gay, exciting things just a while since and that there were gay, exciting things hovering in the next hour.”

-The Great Gatsby, F. Scott Fitzgerald.

In the great novel The Great Gatsby, Daisy, one of the love interests of the book, has a beautiful voice. She's described otherwise, but you don't really remember what she looked like, you remember how she sounded. Fitzgerald describes her voice as musical, running up and down and the scales when she talks. And you know what he's talking about. You hear that voice in your head: light, breathy, utterly charming. You don't really know what she looks like, but from imagining her voice, you know she is beautiful.

What is it about this, or any voice, that makes it attractive? Is it the pitch? The tone? The firmness or breathiness of voice? And what is it about that voice, or any voice, that makes you know that someone is beautiful, handsome, masculine, feminine?

Xu et al. "Human Vocal Attractiveness as Signaled by Body Size Projection" PLoS ONE, 2013.

(Source)

The authors of this study wanted to see what makes a voice a VOICE. What acoustic factors make it most attractive to women and to men? To do this, they first took 10 young men, and had them rate the attractiveness of a female voice saying "good luck on your exams". The voice actor said the phrase without any emotion using three different sound qualities: normal, breathy, and pressed (more of a hard tone). They then took the recording of this voice and modified it up and down, to create the phrase in several different pitches and formats. Specifically, they modified it upward toward what they hypothesized to mean "small body size and happiness" or downward toward what they hypothesized to mean "large body size and anger".

They showed that while increasing the pitch (higher) did not increase the attractiveness of the voice, lowering it decreased the attractiveness. And increasing the breathiness of the sentence increased attractiveness. The authors believe that this means that lowering the voice, and presumably indicating a larger body size (larger body size in general means the normal voice will be lower), reduced how attractive the men found the voice.

But because the voice they heard was a real person, it was possible that differences in her speech could cause the differences. So from here on out they used only artificial voices. They then created the phrase "I owe you a yoyo" (romantic, no?), in male and female artificial voices, with variations in format, pitch, and breathiness, and presented them to men and women (n = 16 each) and asked them to rate attractiveness.

For the men, it was roughly the same, lower pitches became less attractive, and breathiness was more attractive. In theory, if the attractiveness of a male voice was opposite that of a female, the women surveyed should have judged low voices with no breathiness as the most attractive.

But it didn't turn out quite that way. While the women rated the lower pitched voices as more attractive, they also preferred the male voices slightly BREATHY. I can't really even imagine a male voice sounding breathy so I'm a little at a loss for how attractive this may have been. The authors hypothesize that this is due to the fact that a low pitched pressed voice might be seen as too aggressive, and the breathiness is needed to take some of the edge off, so to speak.

When participants were asked how HAPPY they thought the voice was, higher pitches and breathiness were always seen as happier, in males or females, while lower pitches and a flat done rated angry for both sexes.

The authors conclude that men rate as more attractive high-pitched, breathy voices, which indicate small body size, while women rate as more attractive low-pitched, breathy voices, which indicate large body size, but maybe less aggression.

While I'm very interested in the findings themselves, I don't know that I agree with the hypothesis the authors put forward as to WHY certain voice qualities are more attractive. The authors talk about voice quality being a type of secondary sex characteristic, and hypothesize that high voices mean smaller body size while low voices mean larger. By and large, this is certainly true, but I'm not sure that the voice quality itself is an evolutionarily selected trait. First off, because of the fact that voice arises from physiology (the size of the throat involved), you can't actually separate the voice from the body size. People with smaller bodies have higher voices. Does that mean that the voice is what we're after? Or that the SIZE is what we're after? I feel like the two have to vary concurrently, and while that doesn't mean the voice isn't important, it does make the question of size possibly as important.

Secondly, the voice you produce naturally is one thing. The voice you produce CULTURALLY is another. As the authors note, women speak in a higher pitch when talking to a male they find attractive. This isn't just then, though. Couldn't culture specify that women speak in higher voices than 'normal' ALL the time? After all, if that's deemed to be 'feminine'...certainly many cultures in the past and in the present have explicitly or implicitly trained young people in how they should sound, from the bellow on the battlefield to the delicate sighs of a lady. And this may mean that...voices lie. Men may strive for a lower voice that belies a smaller body size, while women seek higher, breathier realms. So while voice is a secondary sexual characteristic, I'm not sure it's an honest signal. And if it's not, is it really meaningful?

I also wonder about the artificial voice. The authors admit that maybe this affected their findings. I wonder if you could get rid of the potential variability of a single human voice by doing what is commonly done when looking at facial attractiveness: use a composite. I wonder if a composite of female voices (or male as the case may be) could produce an average sound that wouldn't be purely artificial (though of course lots of artificial modification would be required).

Finally, while this study looked at whether a voice was "attractive", and had people rank attractiveness...it never specified what that meant. I would be very interested to see this go the extra mile and have people, say, match the voice they hear with a projected body type or facial type. For example, if higher voices are supposed to be more feminine and are more attractive to men, would men associate them with other signs of attractiveness? I imagine that they would, and then it would be interesting to see how variations on pitch and breathiness affected the pairing.

But the next time you hear an attractive voice, stop to think a minute. What makes it attractive? And before you look, what do you think the person connected to the voice is like?

Xu, Y., Lee, A., Wu, W., Liu, X., & Birkholz, P. (2013). Human Vocal Attractiveness as Signaled by Body Size Projection PLoS ONE, 8 (4) DOI: 10.1371/journal.pone.0062397