When it comes to smell, humans can hunt with the big dogs

December 18, 2006|By Jeremy Manier | Jeremy Manier,CHICAGO TRIBUNE

CHICAGO -- Since the most ancient humans lifted their noses from the ground and stood upright, humanity's sense of smell has dwindled to second-class status, a talent we gladly leave to drug-sniffing dogs.

But a new study suggests that buried in each person's olfactory lobe lurks enough tracking skill to make a bloodhound bay with resentment.

If the results are surprising, that might be because no one ever tried putting a bunch of college undergraduates in a field wearing blindfolds and sound-muffling headphones, then having them crawl in the grass after a scent.

When researchers at the University of California, Berkeley did try that, they found that most of the students could follow a 30-foot trail of chocolate perfume; they even changed direction precisely where the invisible path took a turn. What's more, the subjects were able to smell in stereo: When researchers blocked their ability to smell independently with each nostril, the students' scent-tracking accuracy dropped off drastically.

By revealing how noses locate smells, the scientists hope to lay the groundwork for electronic noses that could detect hazards such as land mines. Their work, published online yesterday in the journal Nature Neuroscience, was funded in part by the U.S. Army Research Office.

Other experts say the findings will help rebut the misconception that people stink at following scents.

"What this study highlights most for me is that the human sense of smell is a lot better than many people think it is," said Jay Gottfried, a professor of neurology at Northwestern University.

"It's true that our lives are taken up by visual and auditory streams of consciousness," Gottfried said. "But if you paid more attention to smell, it would become a more prominent aspect of your life."

To focus on the students' olfactory ability, the researchers put together an outfit that one likened to a mobile sensory deprivation chamber. The subjects wore taped-over goggles, earmuffs and thick work gloves to block anything but smell from guiding their way. They also wore devices over their noses to control how much scent each nostril could take in and to measure how fast they were sniffing.

A major reason the scientists studied human subjects is that people are more willing than animals to put up with all the extra equipment the study required.

To create a scent trail, the scientists soaked a line of string in the chocolate scent and embedded it in the grass. The people were set loose on the ground about nine feet away from the trail, then had to find the scent and follow it.

Faced with a tracking task that virtually no person ever has to do, the humans quickly adopted some of the same habits dogs use, zigzagging as they tracked the smell.

Although no one knows for sure why zigzagging is important, one theory is that tracking animals, including people, try to keep a sense of where the boundary of the smell is so they don't lose the trail.

A key observation was that the people did better at tracking when they could sense distinct smells in each nostril. When the subjects wore a device that channeled the same air into both nostrils, their performance lagged.

The researchers said the contribution of the two nostrils is similar to the effect of having two ears.

"When someone drops a coin on the ground, you immediately know where to turn," Gottfried said. "That's because your brain computes the difference in when the sound arrives at each ear and extracts information about where the coin fell."

Gottfried said the brain might use the odor "images" from each nostril to build a spatial picture of the scent trail.

Jeremy Manier writes for the Chicago Tribune.

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