Thursday, December 7, 2023

Subjective Olfactory Perception

Two reasons why we aren't good at talking about smells -- 1. we don't share a common percept, and 2.  
we don't share a common language for smells. 

We're genetically coded to perceive smells differently from one another, with a round number at 30% difference across a population. As far as smelling goes, you could say that many of us are mutants. Or you could say there is no "normal" and therefore no mutant. It's just part of the process of evolution. Because of this difference in smell receptors caused by changes in the genes, there are holes in our perception of smells, holes from a societal level, and so the statistics makes it so that the quality of the data, each individual's perception of an odor combined to that of a group of people, is not so good. 

Next, we don't share a common language for smells. Some of this comes from the above problem, but some of it comes from that fact that lots of smells are "social smells" and so the way we talk about them is first and foremost determined by social context, not by some objective characteristic of the smell itself. An example, sort of related, is that we don't talk about the smell of shit in public, it's just not good manners. Or another person's body odor, or the smell of semen, which is almost never ever ever written, not even the word, in general popular literature (in English; maybe this isn't the case in other languages but I don't know).

These two studies below bring some interesting additions to this idea, that the part of our brain that perceives odors is mediated by a pleasure-reward part of our brain, and that language itself comes in two kinds, social and non-social:

Study sheds light on the neural underpinning of subjective odor perceptions
Sep 2023,

Participants rated 160 odors on 18 perceptual descriptors while under fMRI analysis -- the  orbitofrontal cortex is where the most detailed and subjective percepts reside, and not as much with the amygdala and piriform cortex, regions typically associated with odor processing. 

via Northwestern University, Rhodes College, University of Pennsylvania and NIH National Institute on Drug Abuse: Vivek Sagar et al, High-precision mapping reveals the structure of odor coding in the human brain, Nature Neuroscience (2023). DOI: 10.1038/s41593-023-01414-4

Social vs. language role: Researchers question function of two brain areas
Sep 2023,

Language just got way more complicated:

"A research team led by Prof. Lin Nan from the Institute of Psychology of the Chinese Academy of Sciences found that during sentence processing, the neural activity of two canonical language areas—the left ventral temporoparietal junction (vTPJ) and the lateral anterior temporal lobe (lATL)—is associated with social-semantic working memory rather than language processing per se."

These regions were sensitive to sentences only if the sentences conveyed social meaning. 

These findings are likely to force a major reconsideration of the functional organization of the cortical language network.

via Institute of Psychology of the Chinese Academy of Sciences: Zhang, G. et al, A social-semantic working-memory account for two canonical language areas, Nature Human Behaviour (2023). DOI: 10.1038/s41562-023-01704-8.

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