When aromatherapy was starting to show up on the fragrance industry’s radar back in the 1990s, there was much interest in “objective” ways to measure mood response to scent. This was driven in part by the analytical chemistry mentality of corporate R&D departments. They demanded tangible evidence—a GC trace or a weighable reaction product qualified, mood questionnaires did not.
The upshot was a modest bunch of papers on reactions to fragrance using heart rate, blood pressure, Galvanic Skin Response (sweaty palms), EEG (brainwaves) and other methods from the psychophysiologist’s toolbox. The results were sometimes suggestive but they never evolved into the corporate marketer’s dream: a precise and accurate picture of what consumers thought when smelling a given scent. (It turns out that the best way to assess a person’s mood is just to ask him using standardized scales. Try telling that to a chemist.)
I was reminded of all this by an excellent new study from the University of Dresden. The Dresden team used an infrared pupillograph to measure a test subject’s pupil as he smelled various aromas. Pupil diameter is a sensitive and reliable index of activity in the sympathetic nervous system. For example, the pupil dilates in response to painful stimulation.
The main experiment smells were carefully selected. Phenylethyl alcohol smells like roses and is a “pure” olfactory stimulus. In other words, no matter how high the concentration it does not activate trigeminal nerve endings in the nose, those fibers responsible for sensing irritation or pain. Carbon dioxide is a “pure” trigeminal stimulus. It has no discernable odor, yet at sufficient concentration can tickle or even sting the nasal tissues via activation of the trigeminal nerve endings.
In the Dresden experiment each test subject sat with his head on a chin rest and stared at a spot about five feet away. Stimuli were delivered directly into his nose by a computer controlled olfactometer while the pupillograph recorded the diameter of his pupil. After the eyeball session, subjects rated the smells for intensity and pleasantness using standard 11-point rating scales (“just ask him”).
The results showed that the pupil responds to odor intensity but not odor quality. Pupil dilation was greatest in response to a higher level of carbon dioxide and least in response to any level of rose alcohol. The stronger the odor intensity, the faster the pupil changed size. The perceived pleasantness or unpleasantness of the stimulus made no difference to pupil dilation or response speed.
This is well done study that will set a new standard in the somewhat messy field of olfactory psychophysiology. It’s another reminder that we respond rapidly and unconsciously to nasal stimulation. But even though it’s a clean and satisfying scientific result, I’m afraid it will not set any fragrance marketer’s hair on fire. (“The new Calvin Klein—now with 17% more pupil power!”) But it ought to be enough to keep the chemists quiet.
1 comment:
cool.
i tend to think aromatherapy, as it exists now, is a bit muddled by hippies and magickal thinkers, both of whom i like and neither of whom i rely on for factual information.
that being said, perfume, the synthetic kind, has certainly elevated my mood of late.
though maybe it's just having something interesting to mess with/think about.
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