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New Research: How Our Brains Categorize Aromas

You smell. I do too. Scientists can’t tell us precisely how though.

The physical structures that allow us to sense aromas are well-known, but the way we parse and categorize olfactory information is much less clear. Our sense of smell isn’t connected to the brain through the same pathways as our visual, auditory and tactile sensors. It’s not even connected to the same part of the brain.

A trio of researchers has just published a paper that may improve our understanding slightly. The study is called Categorical Dimensions of Human Odor Descriptor Space Revealed by Non-Negative Matrix Factorization. It’s authors are Jason B. Castro, Arvind Ramanthan and Chakra S. Chennubhotla—a neuroscientist, a computational scientist and an expert in computational and systems biology.

As you may have gathered from the title, it’s written for researchers and experts not the general interest reader. The article assumes considerable prior knowledge, is replete with specialized terminology and features several pages of text such as “we first examined the structure of H, the matrix of odor weights obtained from NMF (recall that H corresponds to an odor), and defines a point in 10-dimensional descriptor spaced spanned by W.” The paper is freely available online though, so you might read it skim it look at the colored charts.

Here’s the gist of it:
As we pick up an aroma, our brain rapidly identifies a number of attributes for the scent. Unlike our sense of taste which we know to resolve just five flavor dimensions (sour, sweet, salty, bitter and umami), there are many potential attributes for smell. They have not been fully identified, prioritized or explained. And the number of these dimensions for any particular aroma is very large which makes analyzing or categorizing the totality of an aroma extremely complex.

The authors applied mathematical algorithms, used in other areas of science to simplify complex, multi-dimensional data, to olfaction. This enabled them to do two things. First, it proved that this particular analytical approach [non-negative matrix factorization] is effective with respect to analysis of smells. Second, the researchers were able to identify what appear to be the ten principal qualities or categories of aromas, each category linked to a number of molecules that generate such aromatics.

These basic categories each have many incarnations but, for simple identification, might be labeled by their most prominent members: fragrant/floral, woody/resinous, fruity (non-citrus), putrid/decayed, chemical, minty/peppermint, sweet, popcorn, pungent and lemon/citrus. Here’s a table showing those categories and the most important members of each.

If you’ve seen wine aroma wheels or aroma categories used by sommeliers or WSET, then the table will look quite familiar. There are interesting differences though. For example, citrus and non-citrus fruit are clearly delineated but non-citrus such as cherry, pineapple and banana are all in the same category. There is also overlap. Cut grass falls into woody/resinous but also citrus. Some attributes are more general characteristics than analogs to physical objects. For example, floral, citrus, sweet and fruity categories can all result in an aroma being described as “light.”

10 vectors
From Categorical Dimensions of Human Odor Descriptor Space Revealed by Non-Negative Matrix Factorization

Further studies using this mathematical technique may break a lot more ground for industries such as wine and perfume. The current analysis was based on a standard set of aromas used by researchers. It may not have included specific notes of interest to us, like oak and aspects of minerality. And it clearly wasn’t a goal to prioritize wine-centric aromas in any way.

I look forward to follow up efforts. Better understanding how our brains naturally categorize wine-related aromas will help us become better analytical tasters. It will also guide us in communicating aromas to consumers in the way they will most readily grasp.

 

Follow NorCalWine on Twitter for breaking wine news, information on events and more. Become a fan and join the NorCal Wine community on FacebookAlso check out our comprehensive Northern California winery listings. They are very useful for planning a tasting trip or just getting in touch with a winery.

This article is original to NorCalWine.com. Copyright 2013 NorCal Wine. All rights reserved.

Comments   

 
Bob Henry
#1 Bob Henry 2013-09-25 00:25
FRED,

IT IS THOUGHT THAT "TASTE" COMPRISES ONE MORE COMPONENT BEYOND THE RECENTLY EMBRACED UMAMI . . . THAT BEING FAT:

From Specialty Food “Food Trends” Section
(March 2009, Page 12):

“Umami 101"

[Link: specialtyfood.com/.../...

By Denise Shoukas
Contributing Editor

One of the five taste sensations detectable by humans, umami helps us distinguish savory, hearty tastes often found in meat, fish, vegetables and dairy products. But how exactly does it work? Researchers from Senomyx (a San Diego, Calif., flavor ingredient development company) and Biopredict (an Oradell, N.J., biotechnology company) have made a discovery that helps explain it.

They wrote in “Proceedings of the National Academy of Science” that the TR1 flavor receptor on the tongue is shaped like a Venus flytrap, allowing the amino acid glutamate that is associated with savory foods to remain in the “trap” longer giving off the umami flavor sensation.

Because of this discovery, food developers may soon be able to find ways to enhance foods with an “umami flavor” to reduce the use of salt and enhance flavors, promoting healthier eating.

AND SEE THIS RELATED ARTICLE . . .

From Specialty Food “Food Trends” Section
(June 2010, Page 64):

“Adding to the Senses: Fat"

[Link: not available ]

By Denise Shoukas
Contributing Editor

Some people love salty, some love sweet. But researchers have discovered another taste sense to add to the list. According to a recent study published in the latest issue of the "British Journal of Nutrition," researchers at Deakin University in Australia have found that in addition to the five other tastes -- sweet, sour, salty, bitter and umami -- fat is the sixth taste people can identify. And those who have a sensitive enough palate to discern this "fat flavor" tend to eat less of it and are less likely to be overweight. The researchers hope that the discovery of this new taste sense will lead to helping people lower their fat intake and aid in the development of new low-fat foods and diets.

~~ BOB
Quote
 
 
Bob Henry
#2 Bob Henry 2014-03-22 10:00
Fred,

From National Public Radio:

"Never Mind Eyesight, Your Nose Knows Much More"

[Link: npr.org/.../...

Excerpt:

"The human eye can distinguish more than 2 million distinct colors. But scientists studying smell now say they have their vision colleagues beat: The human nose, they say, can distinguish more than a trillion different smells.

"Yes, trillion with a T.

"That new figure displaces a much more modest estimate. Until now, smell researchers have been saying the human nose can distinguish about 10,000 smells.

"But Andreas Keller at The Rockefeller University says that number comes from a discredited idea from the early 20th century, which asserted that there are four primary smells, the way there are primary colors. That's just plain wrong."

Link to Science magazine:

"Humans Can Discriminate More than 1 Trillion Olfactory Stimuli - Science Magazine"

[Link: www.sciencemag.org/.../1370]

~~ Bob
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