Researchers have made a groundbreaking discovery that human olfactory perception can detect changes in odors within just a single breath, challenging the previously held view that our sense of smell is slow.
By utilizing a sniff-triggered device precise to 18 milliseconds, they demonstrated that people can discern between two different odors in sequences as short as 60 milliseconds—faster than a blink.
Understanding Olfaction: Speed and Sensitivity
When we breathe in, airborne chemicals enter our nostrils and create what we recognize as odors. These chemicals are expelled when we exhale. Typically, a breath lasts between three to five seconds, which has led to the belief that our ability to detect and differentiate odors is somewhat slow, as all chemical changes perceived within a single breath are thought to blend into a single scent. Traditionally, this has made our sense of smell—olfaction—known for its apparent sluggishness.
However, a recent study led by Dr. Zhou Wen from the Institute of Psychology at the Chinese Academy of Sciences presents a challenge to this notion. Published today (October 14) in Nature Human Behaviour, the research demonstrates that the human sense of smell can indeed detect fine chemical changes within the duration of a single sniff.
Advanced Sniff-Triggered Technology
Dr. Zhou’s team developed a unique sniff-triggered device that controls odor delivery with a precision of 18 milliseconds—about the duration of a frame on a regular LCD display (60 Hz). Using this device, the team created temporal odor mixtures, presenting two odors one after the other with precisely measured delays. They tested 229 participants across five experiments to see if they could distinguish these mixtures.
Unveiling Temporal Sensitivity in Smell
The researchers found that when two odor compounds, A and B, were presented in different orders (A before B and B before A), participants could tell the difference when the delay between the compounds was just 60 milliseconds—about a third of the time it takes to blink. For comparison, the frequency at which flickering green and red lights appear continuous is around 10–20 Hz (50–100 ms resolution).
Participants’ ability to distinguish the odors improved with longer delays between the compounds and did not depend on knowing the correct order. They could distinguish “A before B” from “B before A” by smell, even if they couldn’t identify the order. This ability was not influenced by factors like odor intensity, pleasantness, pungency, or the total amount of odorant molecules in a sniff.
Implications for Olfactory Perception Studies
These findings support the existence of a temporal code for odor identity. By providing precise control over odor delivery that aligns with natural sniffing dynamics, this research opens new avenues for studying the temporal aspects of olfactory perception and developing olfactory displays.
“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,” said Dr. Zhou, the study’s corresponding author.
Reference: 14 October 2024, Nature Human Behaviour.
DOI: 10.1038/s41562-024-01984-8
This study was supported by the Ministry of Science and Technology of China, the Chinese Academy of Sciences, the National Natural Science Foundation of China, and the China Postdoctoral Science Foundation.