PrimaryOdors.org seeks to understand and characterize the encoding of odors from each aroma compound's pattern of receptor stimulation to the perceptual qualities and notes that these patterns evoke. To do this, the website collects dose-response data from scientific publications where research teams have measured the responses of odor receptors to odorants. The site admin, an amateur DIY perfumery enthusiast, has also carried out experiments involving mixing agonists of a target receptor to find what perceptual note stands out above all others, and experiments comparing an agonist mixture with the same mixture plus an added antagonist to determine which perceptual notes the antagonist blocks. PrimaryOdors.org also maintains an in-house molecular docker, PrimaryDock, which natively supports side chain flexions, path-based docking, and other features designed to facilitate prediction of olfactory GPCR responses to ligands. By filling in the numerous gaps in the empirical data with well-designed predictions, it will be possible to find better correlations between receptors and perceptual notes.
What Is a Primary Odor?
Just like color vision is based on primary colors, and the gustatory sense is based on primary tastes, it is reasonable to assume that olfaction would be based on primary odors. One study identified malty as a primary odor, based on the inference that a single class of receptor must be responsible for its detection. There are many glib news and po-sci websites that claim the primary odors are things like "fragrant", "putrid", and "chemical" when in fact these descriptors are way too vague to apply to individual perceptual notes. And at least one scientific article made the bold claim that of course everyone knows there's no such thing as a primary odor, without offering one shred of evidence for such an extraordinary statement.
One can define the term "primary odor" in a few different ways. The odor perceived when neurons containing a single receptor class is stimulated could be considered primary at the receptor level, or a receptor primary, if you like. These would be analogous to the red, green, and blue primaries of color vision, corresponding to the three classes of cone cell in the human retina, though this itself is an oversimplification. There may be receptors whose neurons do not contribute any perceptual notes on their own, but only in combination. In such case, the notes evoked could be considered combinatorial primaries, perceptual qualities that cannot be divided into component qualities, even though they require more than one receptor to produce them. We have an example of a combinatorial primary in human color vision: the color yellow, which requires activation of both red and green cone cells, but is perceptually distinct from both red and green. Finally, there would be perceptual primaries that may or may not directly correspond to either receptor or combinatorial primaries. It can be noted that some odors smell "dark", others "light"; some "smooth" and others "rough"; others variously sweet, sour, icky, wet, dry, green, gray, purple, red, thin, bulky, dirty, clean, etc. In many cases these may be learned associations, but some may nonetheless be extremes of the dimensions of odor space. Those would then be the perceptual primaries. It is a reasonable hypothesis that the receptor primaries and combinatorial primaries probably occupy individual points in perceptual space, and that the perceived odor is either a weighted barycenter point of these inputs, or else a pattern formed by the input points.
This site seeks to identify all three of receptor, combinatorial, and perceptual primaries, or to identify the mechanism of odor encoding if the hypothesis of primaries turns out to be incorrect.
On the Accessibility of Information
There was a time, just a few years before this writing, when a member of the public could enter a university library and access scientific articles full of data on all the latest research. Those days, sadly, are now just a memory. Articles can usually still be purchased, but it would be out of most people's budgets to obtain a thorough understanding of the current state of any one field. Many of the scientific journals are being run as businesses, meaning their incentive is to make a profit no matter what. Consequently, they claim a copyright on their publications, like most publishers have done in other fields such as entertainment. But unlike a song or a movie, scientific papers contain data, obtained by research, representing facts about the world, the universe, or specific organisms, in many cases paid for by public funds. For-profit journals seek to protect their intellectual property, but in so doing, they also gatekeep access to the data. No one owns impersonal factual information, or at least no one should. The recent tightening of access may be a response to the general public's growing tendency to misrepresent scientific discoveries and peddle junk science or even woo-woo interpretations thereof, particularly during a global pandemic, but the fact is these unfortunate tendencies have existed all along. Keeping information out of the wrong minds also keeps it out of some of the right minds, since not everyone is allowed to attend university, and gatekeeping information that everyone should have the right to view and copy will only increase the problem of anti-science in society, not decrease it.
We as a society then should encourage openness and transparency in the sciences, and make it easier for everyone to learn critical thinking and the scientific method. The best time to teach these skills is in the single digits and the teenage years. The churches know this, and they indoctrinate their followers from the very beginning with guilt, fear, and an unquestioning allegiance to a being that has never been observed. Consequently, religious organizations have been very successful for millennia. There was a time when religion had a positive impact on societies (the Visigoths, for example), but we as a species have improved and we now have modern science to explain the things that puzzled the ancients. It is time to evolve forward with empirical, peer-reviewed knowledge. Paywalls are not the way to do that.
About the Admin
I am an amateur science enthusiast with particular interest and knowledge in chemistry and perception. In the past I have gathered empirical data about the retinas of animals, especially microspectrophotometry of photoreceptor cells, in order to understand the color vision capabilities of vertebrate and invertebrate species. (Avian color vision is the best. I've never been fond of pigeons, but I envy them in a way, as they seem to be pentachromats.) I have obtained samples of chemical elements, then using an electric spark, have photographed their spectra resulting in considerably greater accuracy of relative spectral intensities over the visible and (in some cases) near infrared regions compared to the line intensities in for example the NIST Atomic Spectrum Database. Schools around the world include my element spectrum website in their materials for teaching physics. I have also built my own infrared and ultraviolet cameras, using Raspberry Pi technology and carefully chosen glass filters and gels.
All of this was possible with dedication in the face of unfavorable odds. I was largely denied any chance to pursue a higher education by parents who sought to "cheat the system" and only cheated me instead by making it impossible to get financial aid. My education was what they could afford, which was a few credits each semester at the community college, and instead of being allowed to pursue my dreams they told me to settle for computer programming, then enrolled me in a computer networking certificate program instead. Idiots. Despite their best efforts, I succeeded in establishing a good paying career (in computer software development), and in my free time taught myself a great deal of organic and inorganic chemistry.
Even the reasons for bringing me into the world in the first place were based on a weird juxtaposition of a missing person, a surviving family member on a ridiculous spiritual mission, failure to heed a doctor's good advice, all in a matrix of generations of abuse in the family line. People can't be replaced, and grief is a garbage reason to have a kid. The disillusionment at seeing the wrong beliefs I was raised with disproven over and over again led me to become a firm supporter of the scientific method, and a skeptic of all faiths and all forms of spirituality.