Excerpt from the article:
It’s a smelly, complicated world out there. Most of the scents we encounter in nature are actually amalgamations of dozens to hundreds of different odiferous compounds— the “scent” of a rose is composed of over 275 unique molecules. And while we have clearly defined boundaries for human vision (390-750 nanometer wavelengths on the electromagnetic spectrum) and hearing (20-20,000 hertz), it’s proven much harder to gauge the limits of our sense of smell.
That’s exactly what the researchers behind the original Science paper set out to do. They first devised an experiment to determine the resolution of our sense of smell. How far apart do two smells have to be for the human nose to register them as different?
To find out, the authors made a bunch of different mixtures of 10, 20 or 30 odiferous compounds, drawn from a collection of 128 odorants that included familiar scents like orange and spearmint. The mixtures varied in their degree of similarity to one another. The researchers then asked 26 volunteers to perform a sniff test on three vials—two with identical substances, and one with a different mixture—and identify the outlier. Each subject performed this outlier test hundreds of times.
From these 26 subjects, the researchers found that, on the average, mixtures that contained more than half the same odorants tended to smell the same, while mixtures containing less than half the same odorants tended to smell different.