We're In Stereo

From Nature, via 3quarksdaily:

If you think only hounds can track a scent trail, think again: people can follow their noses too, a new study says. And they do so in a way very similar to dogs, suggesting we're not so bad at detecting smells — we're just out of practice.

Scientists have found that humans have far fewer genes that encode smell receptors than do other animals such as rats and dogs. This seemed to suggest that we're not as talented at discerning scents as other beasts, perhaps because we lost our sense of smell when we began to walk upright, and lifted our noses far away from the aroma-rich earth. A team of neuroscientists and engineers, led by Noam Sobel of the University of California, Berkeley, and the Weizmann Institute of Science in Rehovot, Israel, decided to test this conventional wisdom.

The team first laid down a 10-metre-long trail of chocolate essential oil in a grass field (the scent was detectable but not strong or overpowering). Then they enlisted 32 Berkeley undergraduates, blindfolded them, blocked their ears and set them loose in the field to try to track the scent. Each student got three chances to track the scent in ten minutes; two-thirds of the subjects finished the task. And when four students practiced the task over three days, they got better at it.

Next, the team tested how the students were following the trails. They counted how many whiffs of air each student took while tracking the scent trail, and tested the effect of blocking one nostril at a time. The scientists found that humans act much like dogs do while tracking a scent, sniffing repeatedly to trace the smell's source. They didn't do so well with one blocked nostril, suggesting that the stereo effect of two nostrils helps people to locate odours in space.