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Weizmann Institute of Science scientists discovered: white smell

Until today it was common to think that you could see white color and hear white noise. A study by Weizmann Institute of Science scientists reveals that it is also possible to smell a white odor. These findings are published today in the journal of the US National Academy of Sciences (PNAS).

Until today it was common to think that you could see white color and hear white noise. A study by Weizmann Institute of Science scientists reveals that it is also possible to smell a white odor. These findings are published today in the journal of the US National Academy of Sciences (PNAS).

The sense of sight "sees" different mixtures of light waves at different frequencies in the same color - white. The sense of hearing also perceives different mixtures of sound waves at various frequencies as a hum known as "white noise". In order for them to be perceived as "white", the noise and the color must fulfill two conditions: the mixture that creates them must extend over the entire possible range of the stimulus, and the intensity of the stimuli of all the components of the mixture must be the same. Is it possible to use the same principles in the sense of smell to create a white smell? This question has never been tested until now, partly because of the technical difficulties in such research, such as, for example, creating many odorants with the same potency.

Research student Tali Weiss, from Prof. Noam Sobel's research group in the Department of Neurobiology at the Weizmann Institute of Science, led the research on this question, together with Dr. Kobi Sanitz from the same group. They chose 86 fragrances (consisting of a single molecule), which represent the entire range of the fragrance world, and diluted them to the same strength. After that, they prepared different mixtures from these materials, with a varying number of ingredients, which are spread over the entire range of the world of scents, and asked volunteers to compare pairs of mixtures. They discovered that as the mixtures contained a greater number of components, they were classified as more similar - even when the pair of mixtures did not contain any common components. Mixtures containing about 30 or more odorants were perceived by the volunteers as nearly identical.

Prof. Noam Sobel. Photo: Weizmann Institute
Prof. Noam Sobel. Photo: Weizmann Institute

To further investigate the phenomenon, the scientists created different odor mixtures, which they called by a meaningless name - "Lorex". After the subjects got used to the smell of one of the "Lorex" mixtures, they tended to name new mixtures as well, which they had never smelled before, but only if they were mixtures that contained 30 or more substances, spread over the entire range of the world of smells. When the mixtures contained 20 substances or less, the subjects did not refer to them as "Lorex". The "Lorex" - the white smell mixture - was described by the subjects as having neutral properties: neither having a pleasant smell, nor having an unpleasant smell.

"The findings not only expand the concept of 'white' beyond the familiar areas of the sense of sight and hearing, and are not limited to adding the sense of smell to the list of senses in which the phenomenon of 'white' exists. They also touch on the most basic principles according to which the sense of smell works, and undermine the accepted concepts about them", says Prof. Sobel. Contrary to popular belief,

Considering the sense of smell as a "machine" for identifying odorous molecules, the research findings show that the system detects odor as a whole, and not individual odorants. Also the combinatorial concept of the sense of smell, that the identification of mixtures is done by activating different combinations of receptors, now requires rethinking, since the research findings "set a limit" to the combinatorial method when it comes to odor mixtures with a large number of substances.

Research student Adi Yablonka from Prof. Sobel's group, and Dr. Elad Schneidman from the Department of Neurobiology at the Weizmann Institute of Science also participated in the study.

14 תגובות

  1. Hi Tzur. Indeed, in the olfactory epithelium, nerve cells are interwoven, each of which expresses a certain type of receptor (a few cases where one nerve cell will express 2 types of receptors). Humans have about 400 different types of receptors (for comparison, rodents have about 1000 different types).
    You can read more in the following link…

  2. Hello everyone and thanks for the interesting article,

    I see that several people who participated in the research are commenting here, so I wanted to ask if we know how to map the types of odor receptors today?

    For example, I read that the sense of sight includes, among other things, three types of color receptors in the human frequency, green and blue, and the other colors perceived by the mind are a combination of the first three.

    Do you know which smell receptors there are? After all, the whole perception of smell is ultimately an internal experience. The properties of substances in the world are indeed a multidimensional scale, but matter and smell are not the same, just as matter and taste are not the same. Maybe mapping the smell receptors and the type of experience they produce will help understand what the "smell scale" is

  3. For Jubilee:
    The article describes an experiment in which we tested whether it is possible to mask the smell of a rose. We chose 4 main molecules that make up Rose and in addition we created a mixture that contains these 26 molecules and XNUMX other molecules.
    Indeed, subjects who learned the smell of white ("Lorex"), returned six months later and recognized the mixture of these 30 components as Lorex...
    Will the mixture also mask unpleasant odors... it is being tested...

  4. Rebecca,
    The phenomenon of synesthesia, mixing of senses in Hebrew, is familiar and well known. In experiments of this type, the subjects are usually asked to be tested in the experiment about their normal feelings and those who may bias the results of the experiment for one reason or another are filtered out. In any case, I don't think that in this experiment synesthesia was increased or decreased, although it is still worth checking, because the synesthetes would have probably experienced the "white" both in the olfactory dimension and in the other dimension (sight or hearing, for example). This is expected because this is exactly the meaning of synesthesia, the coupling in experience. It doesn't matter in this experiment because what would still produce the experience of "white" is the mixing of smells and this is the new finding here.

    In science, time is the best judge of what is a big deal and what is not. Sometimes a finding that doesn't seem particularly important is the first step towards a revolutionary technology.

  5. I haven't read the whole article but I hope you know what synesthesia is. Because it can confuse you or help you in the tests. Anyway, my daughter had synesthesia and it probably went away with age. With her, every smell had a color and every letter, sound and noise had a color. So what you describe is not a big deal. In synesthesia there is a connection between the different senses and they mix. Over the years we have discovered that many people around us have synesthesia. You can reach me via the email I listed above if needed to better understand the fascinating phenomenon of synesthesia.

  6. Yotam,
    Actually there are, and not just escapes but in many multidimensional phenomena. It's just a bit more technically complicated. One way to do this is through principal factor analysis
    It doesn't always work well, but if there are a few significant components in the multidimensional space (each dimension can be a completely different thing), they can be used to spread out the objects being tested (the scents in this case) along them and thus get a kind of ruler. Note that usually these components are a kind of linear assembly of the other features so that in fact a new feature is created which is different from each of the original features (dimensions). The huge advantage of the method is that it allows neglecting a large part of the less significant components and thus greatly reducing the number of dimensions needed to "capture" the most of the phenomenon.

  7. Lorem,
    The materials tested in this experiment interpret the odor spectrum in a good approximation both in the perceptual dimension and in the physio-chemical dimension. In short, many substances are taken and classified according to the perceptual characteristics of the smell (how the subjects experience/describe the smell, and in the same way build a bank of substances with physiochemical characteristics that include, for example, structural characteristics of the molecule such as typical chemical groups, size, degree of agglomeration and other parameters that affect The activity of the molecule, the degree of its connectivity to the odor receptors, etc. Of course, this is a multidimensional space (in each of the two categories), so the researchers took a sample that represents the odor spectrum quite well, and they show this in the article. In practice, the sample used in the experiment does not cover the entire range because And substances at the ends of the spectrum are usually also toxic and the experiment was carried out on human volunteers...

  8. According to Ipossum, in sound and color there is a canonical order for the components of the spectrum, but apparently there is no canonical way to define an order for the molecules that the olfactory receptors are sensitive to. But why does it bother them that they didn't define an order?

  9. The article talks about the "range" of scents and materials "which are spread over the entire range of the world of scents". The question arises, is there a "spectrum" of smells? How do you even determine the position of the smell along the spectrum? Is this spectrum one dimensional? Or maybe two or three dimensional? Or is there another method to determine this range?

    More clarifications are needed.

  10. Now we need to check whether white smell can mask bad smells, just as white noise can mask noise in hearing.
    It is also worth checking whether pleasant smells have a spectrum of 1 part f (as in audio).

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