Scientists once considered our sense of smell, also known as olfaction, slower and less precise than vision or hearing when studying the five senses. Part of this thinking was because the brain has a limited ability to detect rapid changes in odor during a single inhalation, making the human olfactory sense less accurate than others.
Now, new research led by Dr. Zhou Wen from the Institute of Psychology of the Chinese Academy of Sciences challenges this long held belief. Wen and his team say they have now shown that humans can perceive nuanced chemical differences from scents within just milliseconds of inhaling.
The new study, published in Nature Human Behaviour, demonstrates that human olfactory perception can process subtle shifts in chemical compounds in less time than it takes to blink. This remarkable discovery reshapes our understanding of how fast and sensitive our sense of smell truly is.
A Less Precise Sense
Past assumptions about the human sense of smell stemmed from the idea that because inhaling and exhaling takes several seconds, the brain could not effectively detect rapid changes in odor during a single inhalation. Unlike the sharp, instantaneous detection of light and sound, olfaction was thought to blend all airborne chemicals into a single odor throughout a breath, masking any fine temporal distinctions.
As a result, the nose was often considered a less refined sensory organ, capable only of broad, slow perceptions rather than detecting subtle chemical variations in real time.
Finding More Nuances in Noses
To discover the true power of our human sense of smell, Dr. Wen’s team developed a sniff-triggered device with unparalleled precision. The device controls the delivery of odors within 18 milliseconds—roughly the time it takes for a single frame to display on a standard LCD screen. Using this advanced device, the researchers created “temporal odor mixtures,” which involved presenting two different odors one after the other, separated by carefully measured delays.
Using the device, the team tested 229 participants across five experiments to see if they could distinguish the order of these odor mixtures. When the two odor compounds (labeled A and B) were presented in different sequences (A before B or B before A), the participants could detect the difference between the two sequences with a delay of just 60 milliseconds, one-third of the time it takes to blink an eye.
“A sniff of odors is not a long exposure shot of the chemical environment that averages out temporal variations. Rather, it incorporates a temporal sensitivity on par with that for color perception,” explained Wen.
Participants’ ability to distinguish the odors became more accurate as the delay between the two compounds increased. Interestingly, this ability did not depend on knowing the correct order of the odors, and participants knew the order of the smells by the scents alone—even if they couldn’t articulate the order. Factors like the intensity of the scent, its pleasantness, or the overall amount of odorant molecules present in the sniff did not affect their performance.
How the Brain Processes Scents
These results support the existence of a time component for odor identity, meaning that our brains process the timing of odor exposure as a critical part of recognizing smells. The researchers’ sniff-triggered device, which mimics the natural dynamics of breathing, opens up exciting possibilities for future research into the temporal aspects of olfactory perception.
This study shows that with the timing component factored in, our noses are far more capable than previously thought. With tools that allow for such precise control over odor delivery, researchers are now better positioned to explore how our brains interpret the smells around us—and how this sensitivity could be harnessed for developing new technologies like olfactory displays, digital scents, and more.
Kenna Hughes-Castleberry is the Science Communicator at JILA (a world-leading physics research institute) and a science writer at The Debrief. Follow and connect with her on X or contact her via email at kenna@thedebrief.org