Summary: Human olfactory perception, traditionally viewed as slow, can actually detect rapid changes within a single sniff, as shown by new research.
Using a precise sniff-triggered device, researchers presented different odors in close succession and found that participants could distinguish between them with only a 60-millisecond delay. This challenges the notion that our sense of smell is limited in speed, revealing a temporal sensitivity similar to visual perception.
These findings support a “temporal code” for odor identity, where scent is processed with more precision and speed than previously thought. This advancement opens new possibilities for understanding smell dynamics and creating olfactory technologies.
Key Facts
- Humans can detect odor changes within just 60 milliseconds, a short time span.
- This ability suggests a temporal coding mechanism in our sense of smell.
- Findings could lead to innovations in olfactory displays and research on smell perception.
Source: Chinese Academy of Science
When we inhale, airborne chemicals enter our nose, creating the “odor” we detect. These chemicals are then expelled when we exhale. Each breath lasts 3–5 seconds, which seems to limit how quickly we can perceive odors. Chemical changes that occur within a single breath appear to be combined into one odor. Because of this, our sense of smell, or olfaction, is often considered a slow sense.
Now, however, researchers led by Dr. ZHOU Wen from the Institute of Psychology of the Chinese Academy of Sciences have challenged this view. Their new study, published in Nature Human Behaviour, shows that human olfactory perception can detect fine chemical changes within the duration of a single sniff.
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.
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.
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.
Funding: 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.
About this olfaction and neuroscience research news
Author: LIU Chen
Source: Chinese Academy of Science
Contact: LIU Chen – Chinese Academy of Science
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“Human olfactory perception embeds fine temporal resolution within a single sniff” by ZHOU Wen et al. Nature Human Behavior
Abstract
Human olfactory perception embeds fine temporal resolution within a single sniff
A sniff in humans typically lasts one to three seconds and is commonly considered to produce a long-exposure shot of the chemical environment that sets the temporal limit of olfactory perception. To break this limit, we devised a sniff-triggered apparatus that controls odorant deliveries within a sniff with a precision of 18 milliseconds.
Using this apparatus, we show through rigorous psychophysical testing of 229 participants (649 sessions) that two odorants presented in one order and its reverse become perceptually discriminable when the stimulus onset asynchrony is merely 60 milliseconds (Cohen’s d = 0.48; 95% confidence interval, (55, 59); 120-millisecond difference).
Discrimination performance improves with the length of stimulus onset asynchrony and is independent of explicit knowledge of the temporal order of odorants or the relative amount of odorant molecules accumulated in a sniff.
Our findings demonstrate that human olfactory perception is sensitive to chemical dynamics within a single sniff and provide behavioural evidence for a temporal code of odour identity.
