Sunday, April 3, 2016

From a Haha moment to an Aha moment…Part 1:

In the wine world, the notion of expertise has been the subject of some considerable debunking and derision. One famous source of derision is the white wine/red wine study by Morrot, Brochet and Dubourdieu.* 

In this study, students of oenology were asked to create individual vocabularies to describe a white wine (Sémillon and Sauvignon blend) and a red (Cabernet-Sauvignon and Merlot). They were then invited back to describe the white wine, and that same white wine colored red with anthocyanidins. According to the reports about this study, the students gave “white” descriptors for the plain white wine and “red” descriptors for the white wine colored “red.” In other words they were (supposedly) fooled into thinking the colored white wine was really a red wine. The popular conclusion from this study is that expertise, and especially the descriptors wine experts use, are a joke.

Were these students really fooled by the color into thinking the white wine was a red one? Or was something more complex going on? In the next couple of blogposts I will analyze this study, and show how it may be related to understanding the flavors of tea as well.

But first two questions: do visual cues modulate aroma perception? and if so, what is actually going on in the brain?

Gottfried and Dolan** answered the second of these questions (and by extension, the first as well) by showing odor-picture pairs while the participants were scanned in an fMRI machine. A magnetic resonance imaging (MRI) machine shows what parts of the brain active while a person is carrying out a task, hence the “f” for “functional.” 

In this task, the participants detected odors and viewed pictures, either separately or together. Odor-picture pairs were chosen to either go together (congruent) or not (incongruent), based on whether the picture showed an object matched with the odor or not. A congruent example: the authors paired the odor of vanillin with pictures of ice cream, cookies, cake, and chocolate.

Participants were much faster and more accurate at detecting the presence of an odor when the odor and the picture were congruent than when they were incongruent. Another words, the presence of a matching picture improved the participants’ ability to detect whether an odor was present or not.

The fMRI scans showed why this might be the case. The brain has two major areas where information from multiple senses are integrated, the hippocampus and the orbitofrontal cortex. The role of the hippocampus is to organize sensory input and bring to awareness memories associated with that sensory input. Smell input from the nose is passed to the hippocampus by as few as three linked cells, which is why smell has such a power to evoke memories. The visual system also provides rapid input to the hippocampus, and the links are nearly as few. 

The orbitofrontal cortex lies a few more connections away from smell and vision input, but here sensory input is integrated to give the sensations a quality, for example pleasant or unpleasant, rather than to bring about a memory. 

These two parts of the brain lit up and awareness of the presence of an odor was enhanced when the participants saw a picture usually associated with that odor.

While this experiment does not tell us whether smell identification is improved by the presence of a visual image, it does tell us that when we see a picture of something, say vanilla ice cream (or a red wine or a cup of green tea) we will be more likely to detect the presence of aromas that we expect in those foods, but are less likely to detect the presence of an aroma we don’t expect, even when it is actually there.

As we will see when we discuss the Morrot et al. experiment in more detail, when their participants tasted (or possibly only smelled) white and red wines without actually seeing the color of the wines, they correctly identified the type of wine only 70% of the time—better than chance, but far from perfect, suggesting that red and white wines are not so different and that visual input is critical for “turning on” aroma detection, and by extension the aroma identification system, in the brain so you can tell the difference. In other words, you have difficulty smelling what you can’t see.

* Morrot G., Brochet F., Dubourdieu D. The Color of Odors. Brain and Language, doi:10.1006/brln.2001.2493 

** Gottfried, Jay A., Dolan, Raymond J. The Nose Smells What the Eye Sees: Crossmodal Visual Facilitation of Human Olfactory Perception. Neuron, 39:375-386, 2003.

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