Scientists are thrilled about their latest discovery, which is a new smell, but you won’t be able to sense it until you can go to the laboratory to experience it for yourself.
The smell is dubbed “olfactory white,” because it is the nasal equivalent of white noise, researchers report today (Nov. 19) in the journal Proceedings of the National Academy of Sciences. Just as white noise is a mixture of many different sound frequencies and white light is a mixture of many different wavelengths, olfactory white is a mixture of many different smelly compounds.
In fact, the key to olfactory white is not the compounds themselves, researchers found, but the fact that there are a lot of them.
“[T]he more components there were in each of two mixtures, the more similar the smell of those two mixtures became, even though the mixtures had no components in common,” they wrote.
Almost any given smell in the real world comes from a mixture of compounds. Humans are good at telling these mixtures apart (it’s hard to mix up the smell of coffee with the smell of roses, for example), but we’re bad at picking individual components out of those mixtures. (Quick, sniff your coffee mug and report back all the individual compounds that make that roasted smell. Not so easy, huh?)
Mixing multiple wavelegths that span the human visual range equally makes white light; mixing multiple frequencies that span the range of human hearing equally makes the whooshing hum of white noise. Neurobiologist Noam Sobel from the Weizmann Institute of Science in Israel and his colleagues wanted to find out whether a similar phenomenon happens with smelling.
In a series of experiments, they exposed participants to hundreds of equally mixed smells, some containing as few as one compound and others containing up to 43 components. They first had 56 participants compare mixtures of the same number of compounds with one another. For example, a person might compare a 40-compound mixture with a 40-compound mixture, neither of which had any components in common.
This experiment revealed that the more components in a mixture, the worse participants were at telling them apart. A four-component mixture smells less similar to other four-component mixtures than a 43-component mixture smells to other 43-component mixtures.