September 26, 2022

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Around the world, people like (and dislike) the same scents

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TO THE SWEDES, there are few odours more delectable than the scent of surströmming, a type of fermented herring. To most non-Swedes there are probably few odours more repulsive—the fish has been described variously as smelling like rancid cat litter, vaguely faecal or even corpse-like. In determining which scents people find pleasant and which they do not, surströmming suggests culture must play a sizeable part.

New research, however, suggests that might not be the case. Artin Arshamian, a neuroscientist at the Karolinska Institute in Sweden, and Asifa Majid, a psychologist at the University of Oxford, began with the expectation that culture would play an important role in determining pleasant smells. This was not just because of examples like that of fermented herring. They had noticed from their own previous work that people from different cultures described odours differently. They also knew from past experiments by other researchers that culture was important in determining which sorts of faces people found beautiful. Thus, they expected to see a similar phenomenon with smells.

To study how scent and culture relate, Dr Arshamian and Dr Majid collaborated with researchers from around the world to present nine different groups of people with ten odours. These varied from pleasant-smelling vanilla extract to isovaleric acid, the chemical responsible for the revolting scent of stinky socks. More intermediate odours, which the team thought might split opinions, included octanoic acid with its mildly rancid smell; the sweet-smelling eugenol, which comes from cloves; and the musty octenol, a scent found in many mushrooms.

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The cultures doing the smelling varied widely too. They included hunter-gatherer communities along the coast of Mexico, subsistence farmers living in the highlands of Ecuador, shoreline foragers, swidden horticulturalists living in the tropical rainforests of Malaysia, and city folk from Thailand and Mexico City. All 235 participants were asked to rank odours according to pleasantness. The team compared their results to earlier work on New Yorkers who had been exposed to the same scents.

Writing in Current Biology this week, the researchers noted that pleasantness rankings of the odours were remarkably consistent regardless of where people came from. The smell of isovaleric acid was reviled by the vast majority of the participants, only eight giving it a score of 1 to 3 on the pleasantness scale (where 1 was very pleasant and 10 was very unpleasant). On the other hand, more than 190 people gave vanilla extract a score of 1 to 3 and a tiny minority, only 12 people, found it revolting enough to rate 8 to 10. Overall, the chemical composition of the odourants that the researchers presented explained 41% of the reactions that participants had. In contrast, cultural upbringing accounted for just 6% of the results. Dr Arshamian and Dr Majid point out that this is very different from how visual perception of faces works—in that case a person’s culture accounts for up to 50% of the explanation for which faces they find beautiful.

Even so, while culture did not shape perceptions of odours in the way that it is known to shape perceptions of faces, the researchers did find an “eye of the beholder” effect. Randomness, which Dr Arshamian and Dr Majid suggest has to be coming from personal preferences learned from outside individual culture, accounted for 54% of the variance in which smells people liked. “Olfactory bulb of the beholder” does not slip off the tongue too easily but it too appears to be a real phenomenon.

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