How much of what we smell reaches our CONSCIOUS mind?
I wrote a short piece on How we perceive smells? but that explained the process taking into consideration when molecules enter into our ortho- or retronasal passage from a certain article or source. This piece is an extension of the same but focuses on how many of those odors we really perceive and reach our consciousness. The last one ended on the note “it’s very difficult for us to smell smells like a mixture”, but why is it so? Because the brain has to simplify and focus on what might be worth more to give an overall sensation of perception (where perception is a conscious appreciation of stimulus or energy).
Our nose is exposed to a plethora of odors or aromas at every moment of our existence. It’s obvious that we don’t smell “stuff” all the time because in order for that to happen the molecules from that “stuff” have to cross a threshold limit to reach our consciousness. Our mind isn’t always attentive to these odors, that’s why we seldom are consciously aware of them but such unawareness doesn’t signify that olfaction is not crucial to our conscious experience.
Olfactory receptors are specialized sensory neurons that detect odor molecules dissolved in mucus in the lining of the nose. The receptors produce electrical responses (impulses) in response to odors. The impulses travel via synapses to sensory neurons in the olfactory bulb, then along the axons of these cells to the central olfactory system of the brain, the piriform cortex. But if three molecules namely M1, M2, and M3 are structurally different and trigger the same receptor R1 (which they can do), then these R1 receptors pass on these signals to one or two glomeruli which then pass on to the piriform cortex which might make us perceive the smell of all three or maybe one of them depending on their threshold limit and many other factors. And because there is no affinity of receptors to a single molecule or vice versa, the understanding of the olfactory system is still unfolding.
A study done by Jinks and Laing (1998) found that when people are presented with a mixture of 16 mixed odors (which were recognizable individually by each participant earlier) with the same intensity, they could not identify the highly familiar target odorants due to competitive mechanisms and the subsequent loss of odor identity through changes in the spatial code (the array or form in which odor receptors are located in the olfactory bulb’s epithelium). As expected, their identification accuracy increased as the mixture’s contents were reduced to 8, 4, and 2 odorants. This shows not only that most of what we smell we don’t understand but also that our mind doesn’t pay much attention to such a scrambled mixture of signals. Moreover, this might also be because a wide range of volatile odorant molecules activates a single type of receptors in the epithelium which leads to a formation of a signal with mixed attributes to reach the piriform cortex, part of the brain that drives olfaction. How our brain deciphers that information is still unknown.
So basically there is a limit on how many individual notes a person can identify at a single moment which is 3 for an untrained person and 3-5 for a trained person and is called The Laing Limit. This shows the general limit to sensory processing and not the level of training. Yes, sommeliers and brewers can identify more categories or notes of odor but it’s because of their formation and wider exposure to odors on a daily basis and they don’t just smell the drink once, there is a whole procedure that includes smelling, looking, sipping, drinking, etc. to provide the most educated guess. Most of us while drinking wine or beer seldom think of the odor molecules and perceived notes, so it’s like an excellent football player might not be as good at playing cricket.
References
- Barwich, A. S. (2020). Smellosophy: What the nose tells the mind. Harvard University Press.
- Mammoth Memory: Olfactory Bulb. https://mammothmemory.net/biology/coordination-and-response/sensory-receptors/olfactory-bulb.html.
- Jinks, A., Laing, D. G., Hutchinson, I. A. N., & Oram, N. (1998). Temporal Processing of Odor Mixtures Reveals That Identification of Components Takes Precedence over Temporal Information in Olfactory Memory a. Annals of the New York Academy of Sciences, 855(1), 834-836.
