Human sense of smell is faster than previously thought

Your nose may be more powerful than you think.

In a single sniff, the human sense of smell can distinguish odors within a fraction of a second, working at a level of sensitivity that is “on par” with how our brains perceive color, “refuting the widely held belief that olfaction is our slow sense,” a new study finds.

Humans also can discern between various sequences of odors – distinguishing a sequence of “A” before “B” from sequence “B” before “A” – when the interval between odorant A and odorant B is merely 60 milliseconds, according to the study, published Monday in the journal Nature Human Behaviour.

“We were astonished to observe that participants could distinguish between two odorants presented in one order and the reverse when the latency between the odorants was as short as 60 milliseconds,” Dr. Wen Zhou, lead author of the study and a principal investigator at the Chinese Academy of Sciences in Beijing, said in an email. Latency refers to the time between when each scent is delivered.

“For comparison, the duration of an eye blink is about 180 milliseconds,” Zhou added.

“Our apparatus could be used for therapeutic purposes, such as olfactory training for patients with olfactory loss,” Zhou said. “More broadly, our findings could guide the design and development of electronic noses and olfactory virtual reality systems, which could have significant clinical benefits.”

The researchers, from the University of Chinese Academy of Sciences and the Ohio State University, developed a sniff-triggered apparatus that included check valves – devices that allow odor to flow in one direction – and Teflon tubes, capable of delivering odors to the human nose with a precision of 18 milliseconds. The researchers asked 229 adults in China to wear this device and smell different odor mixtures: two odors presented in quick succession within a single sniff.

The odors included apple-like scents, sweet floral scents, lemon-like scents and onion-like scents. The latency between the two odors was carefully manipulated.

The researchers analyzed whether participants could distinguish between two odors presented in one order and the reverse at different latencies.

They found that, overall, two odors presented in one order and the reverse became “perceptually discriminable” when the two odors were only 60 milliseconds apart within a single sniff, Zhou said.

The researchers noted that they used only four odorants and that it would be beneficial to test a wider variety to determine whether the human sense of smell is more sensitive to certain odor dynamics or compounds.

“This could provide a deeper understanding of the computational principles underlying our olfactory experience,” Zhou said.

The new findings challenge previous research in which the timing it took to discriminate between odor sequences was around 1,200 milliseconds, Dr. Dmitry Rinberg, a professor in the Department of Neuroscience and Physiology at NYU Langone Health in New York, wrote in an editorial accompanying the study in Nature Human Behaviour.

“The timing of individual notes in music is essential for conveying meaning and beauty in a melody, and the human ear is very sensitive to this. However, temporal sensitivity is not limited to hearing: our sense of smell can also perceive small temporal changes in odour presentations,” he wrote. “Similar to how timing affects the perception of notes in a melody, the timing of individual components in a complex odour mixture that reaches the nose may be crucial for our perception of the olfactory world.”

The ability to tell apart odors within a single sniff might be an important way in which animals detect both what a smell is and where it might be in space, said Dr. Sandeep Robert Datta, a professor in the Department of Neurobiology at Harvard Medical School, who was not involved in the new study.

“The demonstration that humans can tell apart smells as they change within a sniff is a powerful demonstration that timing is important for smell across species, and therefore is a general principle underlying olfactory function. In addition, this study sheds important light on the mysterious mechanisms that support human odor perception,” Datta wrote in an email.

“The study of human olfaction has historically lagged that of vision and hearing, because as humans we think of ourselves as visual creatures that largely use speech to communicate,” he said, adding that the new study helps “fill a critical gap in our understanding of how we as humans smell.”