Smell Illusions

[kevin_chen83]

Do any of you out there know if there is such a thing called smell illusions?

[rakuenso]

esters?

[Royston]

Do you mean if we see something that isn't there it's a hallucination, if we smell something that isn't there it's a....

 

Or are you talking about synthesis of aromas, esters et.c

[YT2095]

Olfactory hallucinations have been documented, if that`s what you`re after?

[Leison]

Do you mean if we see something that isn't there it's a hallucination' date=' if we smell something that isn't there it's a....

 

Or are you talking about synthesis of aromas, esters et.c[/quote']

 

 

can we say synthesized aromas "an illusion". Isn't it different from optical illusion?

[ashennell]

can we say synthesized aromas "an illusion". Isn't it different from optical illusion?

 

Our sense of smell is supposed to provide information about substances that smell. Nice smells should imply that perhaps something is good to eat, sweet smells for sugary substances, etc. nasty smells should tell us to avoid things in our environment - rotten flesh, faeces , etc. So there should be a link between the smell of a substance and its chemical properties. Esters and other aromatic substances are olfactory illusions because they break this link.

 

As species go, our sense of smell is pretty poor - we rely on visual info more. We still use our sense of smell - more so than I think is obvious to us. Flavour, for instance, party determined by smell and not just taste. However, the fact that is not that crucial to our survival makes it seem like it is mainly there for aesthetic purposes. Probably why these kind of chemical illusions are not that obvious.

[Royston]

can we say synthesized aromas "an illusion". Isn't it different from optical illusion?

 

Well not really. An optical illusion is created (or in some cases stumbled across) and used to trick the mind.

 

I remember a theme park I visted on a school trip, where one of the rides incorporated different locations in Britain. The one scene that sticks out the most on the ride, was a wax model / cardboard cutout kind of affair that depicted a typical British seaside resort. The smell of icecream was wafting around.

 

The aroma was synthesized (obviously) but it created the illusion you were near an icecream stall.

 

Is that what you're asking ?

[LucidDreamer]

Our sense of smell is supposed to provide information about substances that smell. Nice smells should imply that perhaps something is good to eat' date=' sweet smells for sugary substances, etc. nasty smells should tell us to avoid things in our environment - rotten flesh, faeces , etc. So there should be a link between the smell of a substance and its chemical properties. Esters and other aromatic substances are olfactory illusions because they break this link.

[/quote']

Maybe esters are not really olfactory illusions. Perhaps they smell pleasant for other reasons than the ability to eat substances that have their sense of smell. It could be that esters smell good to us because some edible plants produce similar smells during spring, but the edible portions of the plant are not the parts producing the smell. Maybe the pleasant smells have to do with cleanliness and its link to good health, and thus good genetic quality. I wonder if chimpanzees find the smell of esters pleasant.

[ashennell]

Maybe esters are not really olfactory illusions. Perhaps they smell pleasant for other reasons than the ability to eat substances that have their sense of smell. It could be that esters smell good to us because some edible plants produce similar smells during spring, but the edible portions of the plant are not the parts producing the smell.

 

I'm not entirely certain that this is why certain plants smell good to us. Lets assume it is though. If the relationship between a plants smell and the food it could provide was stable enough that our sense of smell could evolve based on this, then we would expect the plant to have a pleasant smell. This would mean - pleasant smell leads to a good meal. If we can synthesise the odour in a chemical then this is still an olfactory illusion because its not garuanteed to lead to lunch. So in this case the odour does not relate to the chemical properties but to the association with food.

 

I dont think this is why we find the scent of some plants attractive though. Does anyone know about this? I know they try to attract pollenators and also try and discourage herbivores. So why to we like their scent?

 

Maybe the pleasant smells have to do with cleanliness and its link to good health, and thus good genetic quality.

 

I think that this is certainly true, there are of course pheremones as well. If your point is that our interpretation of smells don't always relate to chemical properties of the actually odours then I agree with you completely but this dosn't rule out olfactory illusions at all.

[ashennell]

While we are on the subject of olfactory illusions/hallucinations, does anyone ever percieve smells in their dreams?

[LucidDreamer]

..then this is still an olfactory illusion because its not garuanteed to lead to lunch...

I see your point of view. Since the smell is no longer tied to the original source that had evolutionary significance, then it might be considered an illusion. I was thinking of illusion in the sense that the smell never had any evolutionary significance.

 

While we are on the subject of olfactory illusions/hallucinations, does anyone ever percieve smells in their dreams?

 

I remember dreams where I incorporated an earlier memory of a smell into the dream, but never a dream where I percieved a new smell.

[Leison]

The aroma was synthesized (obviously) but it created the illusion you were near an icecream stall.

Is that what you're asking ?

 

what i mean is when we say optical illusion ,it is to make our sense of sight confused( not to intepret the stimuli clearly enough) but in case of smell whether it be real fruit or synthesized smell of it, what our brain inteprets is correct.

 

Is there any difference between these optical illusions:

1 Mirage

2 An apperance of moving circles in still paper

[Leison]

hellooooooo....

[Glider]

There really isn't such a thing as an olfactory illusion. The olfactory sense is our oldest sense and of all our senses it is the only one that does not project to the thalamus. It sends projections to the older parts of our brains though, including limbic areas associated with emotion and memory, which is why smell is so evocative.

 

This being the case, there is less 'top down' processing involved in the perception of smell. Vision has a huge amount of top down processing involved; we tend to fill in a lot of the blanks and there is a lot of interpretation going on. This makes visual processes easy to fool.

 

The sense of smell on the other hand very involves very little top down processing. It's a very basic sense (relatively), responding only to chemicals. We might be able to synthesize chemicals that 'smell' like other chemicals, but that is a function of the molecules, not the sense, so it can't really be considered an illusion. If we make a molecule that triggers the same receptors as aromatic molecules from, say, strawberries, then it can't really be called an illusion of we say it smells like strawberries. That would be like drawing a strawberry and calling the fact is looked like a strawberry a visual illusion just because it wasn't a real strawberry.

 

However, there are such things as olfactory hallucinations. This is often a symptom of temporal lobe epilepsy.

 

The difference between illusions and hallucinations is that illusions exist externally and hallucinations don't. For example, a mirage (e.g. the appearance of water over a hot desert road) exists as a function of particular environmental conditions and anybody standing in the right place can see it. An hallucination on the other hand is visible only to the person experiencing it.

 

Is there any difference between a mirage and the appearence of moving circles on still paper? Not really, insofar as they are both illusions and everybody (who can see) can see them (so they are not hallucinations). However, there is a difference in their production. A mirage requires little top-down influence. It exists objectively as a function of envoronmental conditions. The movement in the moving circles illusion on the other hand, does not exist objectively. This is a function of top-down visual processing. I.e. we impart the 'movement'.

[YT2095]

While we are on the subject of olfactory illusions/hallucinations, does anyone ever percieve smells in their dreams?

 

yes occasionaly while asleep, but more often when waking up, I keep smelling smoke, like somethings burning like wood or paper and sometimes electrical. it`s that strong sometimes that I`ve even gone looking for the source, but only I seem to be able to smell it? this can last for an hour or so too. I just ignore it now, but often wonder what causes it, it`s never anything Nice, like roses or chocolate, it`s always burning

I`m a smoker, so I recon that`s probably the cause, although it smells nothing like cig smoke.

[Leison]

thanx Glider for your clear and satisfying explanation

[Glider]

You're welcome

[ashennell]

The sense of smell on the other hand very involves very little top down processing. It's a very basic sense (relatively), responding only to chemicals.

 

I agree that smell is a more 'basic' sense and is less influenced by top down processing but this does not mean that there are no olfactory illusions. There is some evidence that smells are context sensitive and that they can be learned. I have put some refs at the end.

 

We might be able to synthesize chemicals that 'smell' like other chemicals, but that is a function of the molecules, not the sense, so it can't really be considered an illusion.

 

The smell of something is a function of the perceptual system and not the molecule. There is not some simple mapping between molecular structure and percieved smell. Smells are context sensitive.

 

 

If we make a molecule that triggers the same receptors as aromatic molecules from, say, strawberries, then it can't really be called an illusion of we say it smells like strawberries. [/qoute]

 

We could also say it gives the illusion of strawberries.

 

That would be like drawing a strawberry and calling the fact is looked like a strawberry a visual illusion just because it wasn't a real strawberry.

 

You are contrasting a proposed olfactory illusion with a poor visual illusion. A fairer (slightly theoretical) example would be :

 

Is a perfect 3D hologram of a strawberry a visual illusion because it looks like a strawberry? I would say that we interpret our percept as a real strawberry. It is not a real strawberry so therefore it is a visual illusion. This same logic could be applied to the olfactory situation.

 

By the way - Steven Pinker provides a quite convincing arguement for why 2d pictures are in fact visual illusions in 'How the Mind Works'

 

Anyways - I can see how these type of olfactory illusions could be debated - I'm sure that not everyone would agree. So I decided to look for some better olfactory illusions -

 

We have found that presenting exactly the same odor stimulus, but with two different labels ... can create an olfactory illusion. So when a given odor is labeled "vomit," people react negatively, but they find the same odor pleasant if it is labeled "parmesan cheese."

 

This is from a report about the paper below. This demonstrates context sensitivity of olfaction and shows that it can be influenced by top-down processing.

 

Perception. 2001;30(3):381-91. Related Articles, Links

The influence of verbal labeling on the perception of odors: evidence for olfactory illusions?

Herz RS, von Clef J.

 

Herz has done quite a lot of research on olfaction including some stuff on how a smells interpretation may be learned.

 

I also found a recent news article - http://www.news-medical.net/?id=12548.

 

It refers to the illusion of taste produced by smell. Maybe this is a gustatory illusion but it is created through the olfactory system so I ain't sure.

 

However, I'm pretty sure that you can't just declare that there are no olfactory illusions.

[Royston]

This seems to become more of a lingual debate than neurological but anyway.

 

If I had a silver platter and I said under the lid is a freshly cooked chicken, and the scent of a freshly cooked chicken was permeating the air. If I then remove the lid to reveal a (da daaar) strawberry (which has been sprayed with a synthesized fragrance of cooked chicken.) Then the 'illusion' is created by the aroma.

 

You wouldn't be convinced I had a cooked chicken under the platter if I simply told you so, you would need the scent of the chicken to be convinced. In this case can we assume that illusions can be created through scent ? You wouldn't even need me to tell you there's a chicken under the platter...you'd just assume that was the case.

[Conceptual]

Sensory illusions like smell illusions can occur from within. This is not uncommon within dreams. If one looks at the circuitry of the brain, data is inputted into the sensory systems and then stored with similar data. This allows us to smell something and know what it is, due to the association. It seems reasonable that the composite data is stored in the brain. If a dream or unconscious potential activates the composite memory one will both think they smell the stimulus and know its association. It not uncommon for a song from the past ot bring one back or activate a extended memory train, that may include smells and tastes.

[ashennell]

Sensory illusions like smell illusions can occur from within.

 

Illusions from within are hallucinations rather than illusions. They are not the same thing.

[intothevoidx]

Phantom smells can be caused by brain tumors.

 

http://www.doctorhoffman.com/wwphant.htm

[starbug1]

On that note...Michael Crichton's novel, The Terminal Man, narrates the life of a man with psychomotor epilepsy. His condition causes him to have uncontrollable violent episodes, and his brain triggers, or misfires, affecting the olfactory senses, generating an awful, fetid smell prior to the epileptic episodes. This is not a smell illusion, though it does show that the brain can produce different scents that can be perceived only by the patient, in this case a violent paranoid with psychomotor epilepsy.

 

It's an interesting, earlier read by Crichton. However, not as good as his later books.

 

http://en.wikipedia.org/wiki/The_Terminal_Man

[susu]

There really isn't such a thing as an olfactory illusion. The olfactory sense is our oldest sense and of all our senses it is the only one that does not project to the thalamus. It sends projections to the older parts of our brains though, including limbic areas associated with emotion and memory, which is why smell is so evocative...............

 

I was thinkin of posting a reply, but when i read ur post i realised taht there was nothing more i cud add. Great response Gilder

[Glider]

Aw....you flatterer you!