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Nostrils Compete to Relay Key Fragrance

THURSDAY, Aug. 20 -- The nose might know -- but sometimes one nostril detects scents slightly differently than the other, new research says.

Researchers say that subtle disparities in perception result from small differences in the time and intensity of a smell arriving at one nostril or the other. They call the difference a "binaural" (two-nostril) rivalry.

In the lab, researchers exposed each nostril of study participants to a different smell at the same time. Instead of the brain interpreting the two smells as a mixture of scents, participants reported perceiving the smells one after the other, "as if the nostrils were competing with each other," Denise Chen, of Rice University in Houston, said in a news release from Cell Press, which is publishing the study online Aug. 20 in Current Biology.

The researchers called this an "olfactory illusion."

"The two nostrils of a person typically have similar olfactory experience at any given time," Chen said. "But in a laboratory setting in which each nostril simultaneously receives a different smell, subjects experience ... one of the smells followed by the other in an alternating fashion."

Prior research has shown that perceptual rivalry occurs with other senses, such as vision and hearing. Humans have pairs of most sensory organs, including eyes, ears and nostrils.

Each eye forms subtly different retinal images of the same object, while each ear "hears" differently based on minor disparities in the time and intensity of sound waves reaching the ear.

Typically, the brain integrates the minor differences into a single representation.

But sensory cooperation has its limits. "When the eyes simultaneously view two different visual images, we perceive the two images in alternation, one at a time," Chen said.

The same is true for the sense of smell. When faced with two equally-strong scents, the brain perceives them one at a time.

Given the nose's reputation as not being as critical a sense to human functioning as sight and hearing, researchers said they were surprised by the strength of the findings.

More information

The American Academy of Otolaryngology has more on the senses of smell and taste.

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Posted: August 2009