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When aniseed does not smell at all like lemon: Sugar helps you tell apart smells,

Thursday, January 29, 2015   (0 Comments)
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Stephan Lewandowsky

Strawberries taste great. So does Rogan Josh or falafel, though perhaps not all together at the same time. What does it mean for something to “taste great”? Wikipedia tells us that “Taste is the sensation produced when a substance in the mouth reacts chemically with taste receptor cells located on taste buds.” But is that it?


There is a lot more to tasting food than the right chemicals tingling detectors on your tongue. That extra bit is what gives food flavor, and it turns out that a lot more than taste is involved in appreciating food or beverages. This should come as little surprise given that an entire profession—the sommelier—has been built around telling people how to drink fermented grape juice (and, perhaps more accurately, how to choose the right variety of it).

Psychologists have contributed a large body of knowledge to the idea of taste and flavor: For example, we know that flavor is the result of “taste, olfactory, and somatosensory information arising from a common location in the mouth, and occurring over a similar time course.” In other words, flavor results from the cross-modal integration of several distinct streams of input: Taste, smell (olfaction), and touch.

If this sounds familiar, it should be—Gary Lupyan published a post on this site a few months ago in which he talked about cross-modal interaction, such as the ability to “hear a face.”

Along similar lines, a recent article in the Psychonomic Bulletin & Review by Richard J. Stevenson and Mehmet Mahmut explored the interaction between taste and smell in forming flavor. One of the fascinating facts about smell is that even though it relies on only one set of receptors, it has two modes of perception: You either sniff environmental smells through your nose, or alternatively, through the “backdoor”–that is, by chewing food which stimulates the olfactory receptors via the internal nares.

Strikingly, people do not recognize the olfactory component that gives rise to their perception of flavor: although a flavor is experienced (e.g., “strawberryness”), we do not recognize the modality from which it arises.

Stevenson and Mahmut set out to investigate this phenomenon of “binding”, that is the seamless blending of different modalities that we are unaware of, but that allow us to enjoy the flavor of Rogan Josh or chardonnay.

In their experiment people were presented with olfactory stimuli (called odorants) and taste stimuli (tastants). The odorants would be foods such as lychee, cherry, lemon oil, vanilla, banana, and so on. The tastants were either water or weak or strong sugar solutions—that is, either pure water or water that was more or less sweet. Across experimental trials, the odorants and tastants were combined in (nearly) all possible ways, and odorants were repeated with different tastants, to zero in on how odor contributed to flavor experience.

On each trial people first put the tastant in their mouth and then smelled the odorant before they rated the odor on a scale of 7 attributes (e.g., how much the odorant smelled of strawberry, or banana, and so on).

The focus of the analysis was on the interaction between tastant and odorant: If the presence of a taste in the mouth automatically activates a shared “taste-smell channel”, then odorants should be perceived better when a taste was present. That is, on this account, the mere presence of a taste (any taste!) should enhance one’s acuity of smell.

The results partially supported this hypothesis: When the odorants were sweet (e.g., banana, strawberry) the presence of a tastant (sweet water) did not enhance the reliability of smell perception. However, when the odorants were non-sweet (e.g., aniseed, lemon oil), the presence of sweet water improved people’s perception. That is, it appears as though stimulating a sensory channel helps us discriminate between stimuli presented in another sensory channel, provided the two are not in conflict with each other—somewhat surprisingly, tasting something sweet helps us discriminate among non-sweet smells.

To understand the counterintuitive nature of this finding, it helps to recognize that this is a bit like saying that listening to punk rock makes it easier for you to differentiate between pictures of Beethoven and Brahms than listening to the Brandenburg Concerto.

Some cultures may well have developed an intuitive understanding of this intriguing relationship between sensory channels: Pickled ginger is often used as a palate cleanser between different types of nigiri, and in Western cuisine sorbet may fulfill the same function.

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