You rate them on a scale, with negative values denoting whether you disliked the smell, and positive if you liked it.
But what are you, and the other participants smelling, and what did the researchers want to learn from this experiment ?
This experiment was performed in 1975, at about the time when a lot of researchers became interested in whether human being produced pheromones like other mammals do*. So this experiment was part of a grander push, to single out what role odour plays in human interactions.
So the researchers wanted to know whether people "liked" the odours they had presented. The researchers didn't tell them until after the trial, although many of the participants has their own beliefs on what they were being tested on.
To quote the article :
Several observers spontaneously told us we were studying either deodorizing products, cheeses, or preservatives for food such as turkey or fish
But this was not the case. The observers were in fact being asked to smell vaginal secretions.
The researchers had recruited four volunteers, we are calling them A B C and D. The samples were taken every other day throughout each volunteers menstrual cycle using a tampon. They did this for four cycles, all while recording their sexual activities.
The researchers also had other requirements for the volunteers:
Use of vaginal deodorants or douches was prohibited during the study, as was the eating of asparagus, garlic, and onions. The eating of broccoli, brussel sprouts, cabbage, chili, curry, kale, pineapple, and sauerkraut was discouraged.
The researchers then put the used tampons in the bottles, to place under the noses of unsuspecting volunteers.
Here are the results that the researchers found:
The top graph shows intensity, and the bottom graph shows pleasantness. These values are based on the ratings of the volunteers, who gave negative values to the smells they disliked. You may also wish to note that there were no positive values on the pleasantness graph, or as I prefer to refer to it, the "least unpleasant" graph. On the day in which the smells were rated the "least unpleasant" also happened to be the days in which the volunteers marked them as the least intense. However, these all appeared to occur during the 3rd phase of the menstrual cycle, the ovulatory phase.
But we are only scratching the surface here. Let us look at how the volunteers rated each individual donor. throughout the study.
Here, we can actually see that there is a lot more variation in how the respondents actually perceived the odors, with volunteers A and B managing to get positive scores on the pleasantness scale. But as the respondents progressed through the study, their odours were judged to be less pleasant. This may be a side effect of the researcher's sampling strategy i.e. tampons really are not meant to be used for nearly every day of the week.
The first graph appears to completely shoot that down the idea of human pheromones, with smells obtained from all points of the cycle scoring below the pleasantness scale**.The fact that they only used four volunteers, and that they didn't see any gender specific effect really suggests that no pheromones were present. I don't know about you, but I think something smells funky about this.
Doty R., Ford M., Preti G. & Huggins G. (1975). Changes in the intensity and pleasantness of human vaginal odors during the menstrual cycle, Science, 190 (4221) 1316-1318. DOI: 10.1126/science.1239080
* Many mammal species possess a special pheromone sensing organ within their nose known as the "vomeronasal" organ. The organ is much reduced in humans to the point where it is likely vestigial. I haven't had the chance to delve into the literature yet, but it seems to be a general consensus that humans don't use pheromones, unless they want to sell a specific brand of perfume.
** Respond in the comments if can guess why this data, encompassing the data from all of the women from the entirety of the experiment might actually have been skewed downwards.