Senses such as hearing and vision can be discussed in terms that most people understand and that are tied to measurable physical phenomena, researchers say.
You have to give hints for how many parts you may expect to find, but otherwise you let the data decide. NMF has been successfully used in many other areas including the financial world and the processing of still images and videos.
An intriguing aspect of the work is that the different qualities seem to be associated with different chemical features, though Castro is quick to stress that more research is necessary on this front. In ongoing work, the researchers are now approaching the problem from the other direction, applying the current research to a bank of chemical structures in an attempt to predict how a given chemical is going to smell.
These organisms are specialists. If, however, the organism could live in any ecological habitat and accept a wide variety of sources as food, it would not make evolutionary sense to have responses to acceptable versus nonacceptable smells wired in.
These organisms are generalists. We can live in any ecological habitat on the planet and survive by eating the available foods. For generalists, the function of olfaction is to learn how to respond appropriately to a particular smell source when it is encountered, and not to hold a predetermined set of responses to particular odors.
Thus animals that are specialists should have innate olfactory responses to prey and predators, whereas animals that are generalists should not. They should be prepared to learn from experience what is good and what is bad. Evidence for this can be found in a number of studies of animal behavior. Moreover, it has been demonstrated that the cue by which these predators are detected is most often olfaction.
For example, both lab-born and wild-reared ground squirrels show a discriminative defensive response to their natural predators, rattlesnakes, as compared to gopher snakes. This discrimination is made on the basis of subtle olfactory cues that differentiate the two snakes. Paul Rozin has discussed the generalist-specialist issue in detail. Even specialist species are able to modulate innate olfactory responses based on experience. For generalists and specialists alike, neophobia —a cautious response to novel foods and odors—is universal.
This response is particularly adaptive for generalists because of the enormous array of possible food choices available and the greater risk of exposure to poisons. What has already been consumed is safe; what is unknown may or may not be safe. The behavior of young humans attests to this. It is only after these smells become familiar or attractive, as a result of appropriate modeling by the adults, that children make discriminative responses. We can see further evidence that learning is the key mechanism by which generalists acquire odor responses if we look at aversions to tastes.
For example, presenting a rat with a sweet-tasting banana-smelling drink and then injecting the rat with lithium causes nausea and creates a conditioned avoidance of this smell in the future. Researchers have shown that the conditioned aversion is to the smell, not the taste, of the substance. Although potentially socially disruptive, the long-term effects of learned taste aversion are clearly adaptive. If poison is ingested, it is best to learn to avoid it permanently, rather than having to repeat the mistake until it kills you.
The key point is that for generalists, banana and pepperoni are not inherently meaningful smells in themselves; rather, their association to pleasure or pain is what makes us interpret them as good or bad. There are important differences between emotional responses to taste and to smell. Research shows that the emotional response to sweet and bitter tastes is present at birth.
Responses to salt and sour tastes are also generally stereotypical, but some physical maturation after birth is required before they are elicited and the concentration of the substance also affects the emotional reaction. By contrast, emotional responses to odors must be learned. All the essential constituents of foods—vitamins, minerals, proteins, carbohydrates, and fats—are odorless. By contrast, some aspects of foodstuffs do have tastes: the sweetness of sucrose, the saltiness of sodium, and the bitterness of many poisons.
Similarly, the trigeminal avoidance response to certain odors may be adaptive because toxic gases are often highly trigeminally irritating. So olfaction can direct our food choices, but only after we learn what the odors mean in relation to the foods in question. A poisonous mushroom may smell somewhat different from an edible one, but there is no a priori poison mushroom smell.
We must learn these differences by experience—preferably in the form of wisdom communicated by other members of our species, not direct contact. It is evolutionarily advantageous for the olfactory system of generalists not to be hardwired to like or dislike any particular odors, but rather to be readily predisposed to learn and remember what is good and what is bad based on experiences with them.
If we, as generalists, must learn our responses to odors, what does this say about the possible benefits of aromatherapy? Aromatherapy is based on the belief that various natural odors have an intrinsic essentially pharmacological ability to influence mood, cognition, and health.
For example, inhalation of mint is said to have a stimulating effect and lavender a sedative effect on our mood and physical state. There is no evidence, however, that these effects are anything but learned associations.
The claim that certain odors can have a relaxing effect and others a stimulating one may be true, but this is because of the acquired meaning of the odors, not any intrinsic potency. Research reports on studies of the effects of odors on moods clearly point to the principle that odors people like induce a pleasant mood; odors they do not like induce an unpleasant mood. Participants in experiments where purportedly pleasant odors are tested will not show the expected mood effects if they dislike the odor being presented.
Moreover, positive mood effects supposedly elicited by pleasant ambient odors can be induced without any odor present. The joys of aromatherapy are in the mind of the smeller, produced not by direct action of the odor but rather by associations the individual has learned to the odor. The context in which we typically encounter an odor helps support its aromatherapeutic effects.
For example, in Western culture, lavender is commonly found in bath oils and soaps. Since people take baths to relax, lavender is easily construed as relaxing.
But as our earlier wintergreen example illustrates, culture can be decisive in eliciting emotional responses to fragrances. If a Martian were given a vial of lavender to smell, my hunch is that she would not become relaxed. In Japan, some work environments, particularly manufacturing plants, use ambient scenting to help reduce worker fatigue and boredom. This manipulation works, but only temporarily. Adding fragrance to a previously unscented room is the equivalent of changing the furniture or putting in new lights.
The change increases attention and makes people more positively aware of their environment, but after a while, these effects diminish. This occurs very quickly with odors. You may have noticed that when you enter a house that has a peculiar smell, it takes about 20 minutes before you no longer smell it. This is because the olfactory system is geared to detect change a novel odor ; but once the novelty wears off, the receptors cease to respond, and you cease to smell it.
This does not mean the smell has gone; it merely illustrates the effect of olfactory adaption. This process can lead to overuse of cologne or perfume by a wearer who no longer can smell the scent from the bottle.
Rest assured that others still can. Any discussion of innate responses to odors invariably turns to pheromones. In one study, women were given T-shirts worn by random men and asked to rank them by how pleasant they were.
HLA is a group of proteins that helps our immune system to identify cells that belong to us and cells that are from something or someone else — and are therefore potential pathogens. The gene complex that encodes for HLA, called MHC, also encodes for some other proteins used in our immune response, and is useful as a shortcut for scientists to see what kind of protections our immune system can offer.
Your HLA profile is very likely to be different to everyone else you meet — though some people, like your close relatives, will be more similar to you than others. From a genetic point of view, it is an advantage to have a child with someone who has a dissimilar HLA profile.
These women put the T-shirts worn by men with the most dissimilar HLA profile first and last the most similar. So they were able to identify the men, and preferred the men, with the best match in terms of immune system genetics.
They didn't know that was what they were doing, of course — it was subconscious. Do humans use genetic information hidden in body odour to choose their partners? It would seem not. In a study of almost 3, married couples, the likelihood of people ending up with a HLA-dissimilar partner was no different to chance.
We might have a preference for certain smells, and there might be a genetic reason for that, but we don't act upon smells when choosing who we marry. People with congenital anosmia the loss of their sense of smell have poorer relationship outcomes , suggests Mahmut in a study with Ilona Croy at the University of Dresden, Germany. Couples who had high HLA-dissimilarity — which presumably happened by chance — had the highest levels of sexual satisfaction and the highest levels of desire to have children.
This link was more strongly seen in women. From fruity to minty to popcorn-y, all smells can be classified as one of 10 types of aroma, scientists say. Taste, vision and hearing can be quantified, but a systematic description of smell has remained elusive. The profiles contained long lists of descriptors — such as "sweet," "floral" or "heavy" — which people had rated in terms of applicability to different odors.
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