When we inhale, airborne substances enter our nose and produce the “odor” we detect. These molecules are then eliminated as we exhale. Each breath takes 3-5 seconds, which appears to limit how rapidly we may detect odors. Chemical changes that occur inside a single breath appear to blend into a single odor. As a result, human sense of smell, also known as olfaction, is frequently thought to be slow.

Breaking the Limits of Olfaction

However, researchers at the Chinese Academy of Sciences’ Institute of Psychology, led by Dr. ZHOU Wen, have questioned this viewpoint. Their new work, published in Nature Human Behaviour, demonstrates that human olfactory sensitivity can detect small chemical changes in the space of a single sniff (1).

Science Behind Fast Sniffing

Dr. ZHOU’s team created a one-of-a-kind sniff-triggered gadget that precisely adjusts odor distribution in 18 milliseconds- roughly the span of a frame on a standard LCD panel (60 Hz). Using this technology, the team developed temporal odor mixes by presenting two scents sequentially with precisely measured delays. They evaluated 229 volunteers in five studies to see if they could discriminate between these mixes.

The researchers discovered that when two odor compounds, A and B, were presented in different orders (A before B and B before A), participants could discern the difference even when the delay between the compounds was only 60 milliseconds- roughly one-third the time it takes to blink. For reference, the frequency at which flickering green and red lights display continuously is approximately 10-20 Hz (50-100 ms resolution).

Temporal Coding: A New Frontier in Scent Perception

Longer pauses between compounds boosted participants’ ability to recognize the scents, and it was not dependent on knowing the correct order. Even though they couldn’t identify the order, they could smell the difference between “A before B” and “B before A”. This capacity was unaffected by parameters such as odor intensity, pleasantness, pungency, or the overall number of odorant molecules in a sniff.

What We Can Learn from Millisecond Differences

These findings provide evidence for the existence of a temporal coding for odor identification. This study opens up new possibilities for researching the temporal elements of olfactory perception and constructing olfactory displays by giving precise control over odor delivery that is consistent with natural sniffing dynamics.

“A sniff of scents is not a long exposure photograph of the chemical environment that smoothes out temporal fluctuations. Rather, it includes a temporal sensitivity comparable to that of color perception,” stated Dr. ZHOU, the study’s corresponding author.

References:

1. Human olfactory perception embeds fine temporal resolution within a single sniff
   (Wu, Y., Chen, K., Xing, C. et al. Human olfactory perception embeds fine temporal resolution within a single sniff. Nat Hum Behav (2024). https://doi.org/10.1038/s41562-024-01984-8)

Source-Medindia