You Smell (Better Than You Thought)
Dec. 17, 2006 — -- Down on all fours, blindfolded, noses to the ground, a group of college students found their way across a field by sniffing out a chocolate-scented trail.
No, it wasn't a fraternity hazing. It was part of a scientific study that yielded new insights into the human sense of smell.
Scientists have long understood the benefits of two eyes and two ears, but the need for two nostrils remained a mystery. They were so close together that surely one, two, or three holes would be of little consequence for picking up scents.
"We debunked that," Noam Sobel, the professor at the University of California, Berkeley who headed the study, told the Associated Press.
The study, which will be published in the January issue of Nature Neuroscience, indicates that each nostril receives independent information about smells and space.
The Berkeley research team conducted five experiments. The first involved suiting up participants with thick gloves, knee pads, and blindfolds to assure that all they had left was the use of their nose. Under these sensory-deprived conditions, 66-percent of the 32 undergraduates tested made it from one end of the 30 foot chocolate twine trail to the other. This demonstrated that humans, much like dogs, can track scents.
The second experiment tested whether the smellers could improve with a little training. After two weeks of sniff-practice, the participants were, on average, more accurate and faster. Could humans then be trained to scent-track as well as dogs?
The answer: probably not. People aren't exactly used to crawling on all fours. And, while humans sniff about once per second when tracking, dogs sniff four to six times a second.
From Two Nostrils to a Robotic Nose
Next, scientists went into the lab to visualize the air flowing into the nose.
"When you take a sniff, you're not just getting one big diffuse cloud. You're actually getting two distinct air streams," explained Jess Porter, the lead author of the study.
Finally, the researchers put their nostril theories to the test by going back to the field for more scent-tracking, but with new conditions: one nostril taped shut, and a device to confine the nostrils to a shared air stream. Without their noses in tact, the sniffers were slower and less accurate.
Thus two nostrils, it seems, are better than one. And humans might just be better smellers than anyone bothers to notice.
"There is a lot of comparison of our sense of smell to other species, like dogs," Porter said. "People are quick to say we stand upright, our nose isn't on the ground, we have good eyes and sense of hearing and we don't need a good sense of smell anymore."
But it's not that people can't smell well, it's that they don't always try.
"Loss of the ability to smell is a loss of demand we place on our nose," Porter added.
The new nostril information could pave the way to new technology -- even a robotic nose. Sobel is interested in the development of electronic noses, which could eventually replace animals in such dangerous tasks as mine-clearing.
For the full study, visit: http://www.nature.com/neuro/journal/vaop/ncurrent/index.html.