Two ears locate a sound by comparing them, and the received view is that two nostrils do not work that way for smell. Testing it needs the nerve kept out of the way, because a pungent odor stings as well as smells and the sting is locatable. So blindfolded participants hunted an odor source at two meters and at 0.4 meters, with both nostrils open or only one, using a pure smell and a pungent one.
The second nostril helped, for the pure smell only. With , a relatively selective olfactory stimulus, more localization trials were completed correctly using both nostrils than one. With cineol, which has a strong trigeminal component, the number of correct trials did not differ. In the condition people located the source in 72 to 80 percent of trials regardless, and accuracy was better close up.
Hearing locates a source by comparing two ears. For smell, the general view has been that humans cannot do the equivalent. Any apparent ability was credited to the trigeminal nerve, which senses irritation rather than odor and whose endings give a locatable sting.
Separating the two requires two stimuli. Phenylethyl alcohol is a relatively selective olfactory stimulus with little irritant quality. Cineol has a strong trigeminal component. Blindfolded young participants had to locate a source at two meters, the far-field condition, and at 0.4 meters, the near-field condition, with either both nostrils open or only one.
The results split along exactly that line. For cineol, with its trigeminal properties, the number of correct trials did not differ between one nostril and two. For phenylethyl alcohol, more localization trials were correctly completed with both nostrils than with one.
Distance mattered separately. In the near-field condition correct localization was possible in 72 to 80 percent of trials, irrespective of odorant or number of nostrils. Accuracy measured as from the source was significantly higher close up than far away, independent of the odorant. The authors conclude that odor localization in the open field is difficult but possible, and that humans do seem to exploit a two-nostril advantage as the task gets harder.
wat. Two nostrils beat one at finding a pure smell, and made no difference for a pungent one the nerve endings can feel.
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It corrects a textbook claim rather than adding to it. Humans do appear to exploit a two-nostril advantage, and it only becomes visible once the task is hard enough and the stinging component is removed.
How do we know?
Welge-Lüssen and colleagues tested blindfolded young participants locating phenylethyl alcohol or cineol at two meters and at 0.4 meters, with two nostrils open or one, recording correct trials and spatial deviation from the source.
What is still unknown
Young participants in an open-field laboratory task with two odorants. Localization was difficult throughout, so this establishes a small advantage rather than a usable ability to track smells.
Learn something?
Where to next
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