How can you tell if a person is male or female just by their voice? In general, men have deeper voices than women. However, according to a study conducted by Lal Zimman, a doctoral student at The University of Colorado - Boulder at the time of his research, the style of speech can impact perceptions of a person's gender as well, not simply the pitch of his or her voice. In fact, the letter "S" can, on its own, impact people's perception of the speaker's gender.

Zimman studied 15 transgender individuals in the San Francisco Bay Area who were in the process of transitioning from female to male. As part of the transition, Zimman's participants received the hormone testosterone in order to lower the pitches of their voices. Zimman recorded the participants, taking care to measure the frequency of the letter "S". In order to determine the effect that the letter had on 10 listeners, he digitally manipulated the frequency of the speaker's voice, sliding the pitch higher and lower. The listeners then had to assess whether the speaker was male or female.

Zimman found that the speaker could talk with a higher-pitched voice and still be considered as perceived as male if the person pronounced the letter "S" at a lower frequency, which is achieved by moving the tongue away from the teeth as the letter is pronounced. "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," Kira Hall, Zimman's doctoral advisor and an associate professor in linguistics and anthropology at the University of Colorado-Boulder, said in a statement. "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, or whether it appears that the voice comes from the head or the chest, also impacted the perception of gender. It is the result of both practice and biology. For example, people with deeper resonance are born with their larynxes sitting lower in their throats, but children learn to manipulate their placement from early ages. In general, boys learn to push them down when they are young, while girls learn to push them up.

Zimman's study will be presented at the annual meeting of the Linguistic Society of America.