Helen - Dr Martie Haselton is Assistant Professor at UCLA and she works on the changes we see in behaviour when women are at their most fertile. We have Martie on the phone now. Hi Martie. As well as sending out valentines cards what other ways do we broadcast our fertility?
Martie - We found in several studies there are cues in the fertility cycle. There are subtle ways that women might be revealing when they are in the fertile window of their cycle. Whether they are near ovulation, the time when a woman is likely to conceive. In one study we found that women wore more fashionable clothing during that time. In another study that was just published that women voices became more feminine on high fertility days.
Helen - How do you mean more feminine?
Martie - Specifically we recorded the women's voices at two points in the cycle: one during the fertile window during ovulation and several days beforehand and then another period shortly before that but before menstrual or premenstrual days. We did hormone tests to verify that women in their high fertility window were in fact close to ovulation. We took our vocal clips and submitted them to acoustical analysis to see what the differences were between them.
Helen - We have a couple of those recordings now. Shall we have a listen to those and see what they actually came out like? First we have one that came at the low fertility part of the cycle.
"Hi, I'm a student at UCLA" during a low fertility part of the menstrual cycle.
Helen - We should point out, actually, that we've changed the voices a little bit so you can't recognise who that is. It's a little bit robotic but that's just to keep their identity hidden. Shall we listen to the same person at a different, more fertile time of the cycle?
"Hi, I'm a student at UCLA" during a high fertility part of the menstrual cycle.
Martie - That's a great example. The thing we found that differentiated high fertility voices for most was vocal pitch. Women's voices are higher in pitch than men's. This is one of the things that differentiates the sound of a male and female voice. Hormones are associated with the onset of those sex differences. When girls go through puberty their voices begin to sound more feminine. Particularly they become higher in pitch relative to boys of the same age. We suspected that oestrogen might play a role in this and it might show differences across the cycle because oestrogen varies across the cycle along with other sex hormones, which is precisely what we found.
Helen - It seems it could be these hormones that are changing our voices. I presume, are we aware of this at all? I don't suppose we are...
Martie - No, I don't think we're aware of any of these subtle clues of ovulation. In another study that we did we found that women reported feeling sexy and more attractive on high fertility days in their cycle. They didn't know, we weren't asking them, "it's a high fertility day of your cycle, how do you feel?" Instead we just asked them questions repeatedly, over a series of 35 days and we found that they reported a slight upswing on near ovulation and how attractive they felt. It's possible there are many cues that are linked with attractiveness including vocal femininity that change across the cycle.
Helen - A lot of women these days are on the pill which means that their hormones aren't moving up and down in the same way and we don't have those peaks in fertility because our bodies are being convinced that they are actually fertile all the time. Do we know if that's having any effect? Are women on the pill putting out different signals?
Martie - One of the clues in the voice study was that women on the pill - around menstruation there is thought to be a phenomenon of vocal hoarseness. Professional singers report this. There's also some suspicion that women on the pill, professional singers, suffer from a detriment in their vocal ability. It's possible that by taking the pill these cues that we naturally vary across the cycle are blunted and removed. The voices might be overall slightly less feminine. We don't know that from our research but that was some of the speculation that led us to do the study.