( subjects. He suggested this was done t...)Study shows humans have ability to track odors, much like bloodhounds

Since then, however, scientists have had difficulty replicating his experiments, according to Sobel. One explanation for this failure was that von Bekesy used chemicals that stimulate not only the olfactory nerve in the nose, but also a nasal sensory nerve, the trigeminal nerve. Most odors stimulate both, and some, like onions and ammonia, are stinging enough to bring tears to the eyes. Perhaps, some suggested, von Bekesy's subjects were localizing odors based on trigeminal nerve stimulation, not olfactory nerve stimulation.

To eliminate this confusion, Porter and Sobel used two odors with minimal trigeminal 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, which smells like banana. They delivered the odors through a specially designed 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 couldn't smell at all, a condition known as anosmia.

Normal subjects, 16 in all, were able to tell which nostril was receiving a squirt of scent, but anosmic volunteers could only localize the trigeminal odorants, Sobel said. This shows that humans are able to localize odors 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. Subsequent experiments not yet reported, however, provide additional support for their hypothesis that the ability to localize odors to one nostril or the other is realistic.

The experiments were conducted with the subjects' heads inside a functional MRI to
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Source:University of California - Berkeley