August 24, 2009

Study: Nostrils alternate processing odors

A U.S. study finds when the nose encounters two different scents simultaneously, the brain processes them separately and alternately through each nostril.

Rice University scientists say their finding marks the first demonstration of perceptual rivalry in the human olfactory system.

Our discovery opens up new avenues to explore the workings of the olfactory system and olfactory awareness, said Assistant Professor Denise Chen, who co-authored the research paper with graduate student Wen Zhou.

For the study, 12 volunteers sampled smells from two bottles containing distinctively different odors. One bottle had phenyl ethyl alcohol, which smells like a rose, and the other had n-butanol, which smells like a marker pen. The bottles were fitted with nosepieces so that volunteers could sample both scents simultaneously -- one through each nostril.

During the sampling, all participants experienced switches between smelling predominantly the rose scent and the marker scent -- an experience Chen called 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. Although both smells are equally present, the brain attends to predominantly one of them at a time.

The study appears in the early online edition of the journal Current Biology and will appear in its Sept. 29 print issue.