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Rethinking the senses

By CPL Aromas - 17/07/2018

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The experts at CPL Aromas discuss the 'miracle' of smell and explain why coffee smells better than it tastes!

New research has shown that the senses as traditionally conceived are not as distinct as was once thought, according to Professor Barry Smith (pictured, left), Director of The Centre for the Study of the Senses (CenSes), part of the Institute of Philosophy at the School of Advanced Study at the University of London.

In an interview published by the fragrance house CPL Aromas, in its magazine Forecast, Prof Smith says: "I realised that we had our view of the senses all wrong. It came to me through my interest in wine-tasting and how taste actually works. Taste is always a mixture of taste, touch and smell. I realised that, like taste, our experience is always an amalgam of the senses".

Asked about interoception, the awareness of what is going on inside our bodies, he explained: "We now know that it's not just the brain but the relationship between the brain and the heart that regulates our emotions. There is a channel of information going from the brain to the heart and in the other direction. The heart beat changes. This means there are different signatures for different emotions. So when your body is feeling and expressing an emotion, the brain often learns about it through changes in the heart. If you are able to access that channel and use the information, you will be more aware of your own emotions".

Turning to the sense of smell, he expressed the view that people might be accurate about background information of odours without knowing they are. We unconsciously use this information without awareness. Yet other people think they have an acute sense of smell but they don't. It is that they are particularly conscious of certain odours that they dislike and attend to those closely. "It doesn't follow that they very good at discriminating or identifying odours," said Barry Smith.

He described a hotel where he immediately feels relaxed. When he asked about their ambient fragrance, his guess proved correct: the hotel owners pulsed lavender at a very low level through the air conditioning. "If an odour is pulsed, you don't habituate so easily; and not noticing the odour can have the most fantastic effect on you".

Discussing the senses, Prof Smith says that: "Sight takes up a third of the brain's processing power and we attend to our senses of sight and of hearing and maintain a permanent visual scene, whereas we don't maintain a permanent olfactory scene.  It becomes the unnoticed background of consciousness.  The sense of smell is there to alert us to change. Largely, smell's job is to alert you to danger, or something exciting, or appetitive. [That is until] perfumers get us to pay special attention to something and our attention is captured".

Smell has traditionally been thought of as something that invades us. . "Getting up close and personal with a smell or a taste is something that you take into yourself," he said. "Smells and tastes are the ways by which our senses police the boundary between the outside and inside. We neglect our sense of smell, to our detriment." He points out that smell is always modulating our mood and experience. It is like being intoxicated. "We can be enticed by a fragrance, but we feel if we got too much of it, [the odour] might overcome us".

We are said to have two senses of smell, or that smell functions in two different ways. One of these is when we inhale odours from the world, breathing in through the nose - known as orthonasal olfaction. The other is when we breathe out and odours go from the mouth up to the nose at the back of the nasal pharynx - retronasal olfaction. When you breathe out you can intensify the flavours you're getting in the oral cavity.   

The biologist and psychologist Paul Rosen spoke of two types of pleasure association with these two types of smell. With orthonasal olfaction, it's the pleasure of anticipating food, for instance, as a result of the scent of cooking. Then there is the pleasure of reward when the food is in your mouth. You want the two to match but sometimes they mismatch.
 

Coffee is a good example, says Smith. "The smell of freshly-brewed coffee is wonderful and attractive. As you swallow it you think it hasn't got that same fabulousness you get from smelling it".  The reason is that odours won't be identified in exactly the same way going through the two different smell routes. Secondly, you'll already have stripped off around 300 volatiles of coffee through your saliva".

He also commented on the effect of the trigeminal nerve which is important to the sense of smell. He said: "Almost every odour has a trigeminal component to it. This nerve serves the eyes, the nose and the mouth and because it's serving all three, when you irritate the trigeminal nerve endings in the mouth the eyes will water too so they're protected from threat. That is why onions make you cry. Pepper and chilli also have trigeminal effects. These effects relate to our experience of odours. There are two pathways for this effect - one that makes everything taste hot (mustard) and one that responds to peppermint, making everything taste cool".

Carbon dioxide is a pure trigeminal stimulant also, so with sparkling drinks, a lot of the smell delivery is influenced by the trigeminal effect.

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He went on to say that maybe only around a third of the population has ‘odour imagery' but that there is no data on this. Smells seem to have textures: citruses are light molecules, often described as ‘high' notes and this may combine with trigeminal patterning. "Most of us can visually imagine a room in our home as if we are looking at it... Could we do that with smells?" Part of the problem is that it's difficult to ‘code odours'. When we talk about the smell of the sea we are describing a combination of about a thousand volatiles but these are naturally occurring things that humankind has smelt for generations so it's just ‘the smell of the sea'.

As Smith said: "Colours are very well behaved. You can break them into their primary colours, their mixtures, you've got agreement about what is blue and what is turquoise. But with odours there are no primary scents from which others are made. There is nothing that tells us which are basic and which are constructed. And that's wonderful. Complex scents strike us as a single thing - it's a kind of miracle!"As Smith said: "Colours are very well behaved. You can break them into their primary colours, their mixtures, you've got agreement about what is blue and what is turquoise. But with odours there are no primary scents from which others are made. There is nothing that tells us which are basic and which are constructed. And that's wonderful. Complex scents strike us as a single thing - it's a kind of miracle!"