According to a new small study by scientists from the University of California, Berkeley the brain is set up to pay attention to the difference between what the left and right nostrils sense, much the way it can localise sounds by contrasting input from the ears.
The researchers say that it has been "very controversial" whether humans have the ability to do egocentric localisation, that is, keep their head motionless and identify the spatial source of an odour.
"It seems that we have this ability and that, with practice, you could become really good at it," says study co-author Noam Sobel, associate professor of psychology at UC Berkeley.
For the experiment student volunteers were presented with odours to one nostril or the other. They could reliably discern where the odour was coming from, report the researchers, that tracked developments using functional magnetic resonance images of their brains.
The co-authors Porter and Sobel used two odours with minimal trigeminal (nasal sensory) stimulation - essence of rose (phenyl ethyl alcohol) and cloves (eugenol) - as well as two trigeminal odorants - propionic acid, which smells like vinegar, and amyl acetate, that resembles a banana smell.
They delivered the odours through a mask with an artificial septum that provided separate air flow to each nostril.
In addition, they conducted similar experiments on five volunteers who had no olfactory nerves and therefore could not smell at all, a condition known as anosmia.
The 'normal subjects', 16 in total, were able to tell which nostril was receiving a squirt of scent, but anosmic volunteers could only localise the trigeminal odorants, reported Sobel. This shows that humans are able to localise odours through the olfactory nerves alone.
"One possible objection is that the experimental set-up, with a mask that provides separate air flow to each nostril, is artificial. How behaviorally relevant is that?"said Porter.
But they underline that subsequent experiments not yet reported, however, provide additional support for their hypothesis that the ability to localise odors to one nostril or the other is realistic.
In future experiments, UC Berkeley biophysics graduate student Jess Porter and Sobel plan to train volunteers to track odours in the field and test the limits of odour localisation in humans.
Full findings are published in the 18 August issue of the journal Neuron.
Research on chocolate smells reported onearlier this month found that olfaction is uniquely a "dual" sense, in that the brain perceives the same smell molecule differently if it arrives through the nose rather than the mouth.
Researchers at Yale University in the US report the smell of chocolate activated different brain regions according to whether the odour was sniffed or tasted.