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Our Nostrils Share A Rivalry Too

August 20, 2009

Your nostrils may seem to be a happy pair, working together to pick up scents. However, a study published online on August 20th in Current Biology, a Cell Press publication, reveals that there can actually be a kind of rivalry between the two.

“The two nostrils of a person typically have similar olfactory experience at any given time,” said Denise Chen of Rice University. “But in a laboratory setting in which each nostril simultaneously receives a different smell, subjects experience an olfactory illusion. Instead of perceiving a constant mixture of the two smells, they perceive one of the smells followed by the other in an alternating fashion, as if the nostrils were competing with one another.”

Chen and her colleague Wen Zhou call this duel between nostrils binaral (meaning “two-nostril”) rivalry.

In fact, this sort of rivalry of the senses has been observed before. Most of our sensory organs come in pairs: eyes, ears, and nostrils. Typically, the two eyes form slightly different retinal images of the same object, the researchers explained. There are likewise small differences in time and intensity between a sound arriving at one ear versus the other, as well as between a smell arriving at one nostril versus the other. Most of the time, our brain integrates these minor differences and generates one stable and accurate representation of the world around us.

But that kind of harmony can only go so far. “When the eyes simultaneously view two different visual images, one for each eye, we perceive the two images in alternation, one at a time,” Chen said. Similarly, when alternating tones an octave apart are played out of phase to each ear, most listeners experience a single tone oscillating from ear to ear.

The new study shows that the same is true of our sense of smell. Chen says the finding tells us that although both smells are equally present, our brain primarily attends to them one at a time.

The strength of this effect came as something of a surprise to the researchers, especially given that the sense of smell is generally considered less prominent in human perception than our ability to see and hear. Chen says the discovery will undoubtedly stimulate new research on the workings of the olfactory system and olfactory awareness.

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