New research reveals remarkable sensitivity of human sense of smell
What's the story
Contrary to what we previously believed, recent research indicates that the human sense of smell is extremely sensitive and can detect the order of odors at intervals 10 times shorter than previously thought.
The finding refutes Charles Darwin's claim that our sense of smell is "of extremely slight service" to humans.
Scientists have long underestimated our olfactory abilities, deeming them rather sluggish.
Olfactory research
New study challenges traditional perception of smell
Dr. Wen Zhou, the Chinese Academy of Sciences co-author of the research, compared each sniff to "taking a long-exposure shot of the chemical environment."
She said that when a smell is detected, it usually comes across as one scent instead of a distinguishable mixture of odors arriving at different times.
Additionally, she said sniffs are usually spaced by seconds.
Smell experiment
Innovative research reveals rapid olfactory response
Including Zhou, the research team has found that our sense of smell works way faster than we had imagined.
They propose that humans are as sensitive to rapid changes in odors as they are to rapid changes in color.
The difficulty, as Zhou says, has been to create a setup where different smelly substances can be presented in a precise sequence within a single sniff.
Smell apparatus
Researchers develop apparatus to test olfactory sensitivity
In their study published in the journal Nature Human Behaviour, Zhou and her team reported creating an apparatus that let them present different scents in a precise sequence within a single sniff.
The apparatus featured two bottles with different scents connected to a nosepiece with tubes of varying lengths.
These tubes were fitted with miniature check valves that opened when the participant took a sniff.
Olfactory test
Experiment reveals rapid discrimination of odours
The apparatus enabled the two scents to hit the nose at slightly different times during a single sniff, with a precision of 18 milliseconds.
The team experimented with 229 participants, showing them an apple-like odor and a floral scent.
Participants were asked to sniff twice and report whether the order of the odors was the same or had been reversed.
Test results
Participants successfully identify odour sequence
The results revealed that participants correctly identified the order of the odors in 597 out of 952 trials, or 63% of the time.
Similar results were observed when another group of 70 participants carried out the trials with lemon-like and onion-like odors.
Further tests revealed that participants could discriminate between two odors presented in one order and in reverse even when they arrived at the nose just 40-80ms apart.
Perception influence
Odour order shapes perception, study finds
While participants could detect a change when the order of odors was switched, they struggled to identify which scent came first.
They were only successful in identifying the first scent for lemon and onion-like smells when the odors reached the nose with an average time difference of 167ms.
Zhou indicated that distinguishing between two temporal mixtures does not rely on accurately identifying the sequence of the individual odorants.