Food for thought
According to a recent article in The Atlantic Monthly “Tasting a Flavor That Doesn't Exist”, food companies are now implementing the findings of recent research on “phantom aromas” that somehow trick the brain into “manufacturing a taste”. While we can’t really expect non-technical magazines to necessarily convey the complexity of most research, this type of article nevertheless annoyingly perpetuates the idea that somehow the brain is an organ that “we” can easily confuse by feeding into it contradictory or incomplete information. This idea has a long history in the realm of visual illusions. Lines can seem longer than they are, rooms smaller, and the moon larger if we provide the brain with visual information in the right way or under certain constraints. What a silly old brain!
But of course, our brains (that is, us) do not process sensory information out of context. Since the context may tell us something quite important about what we are sensing, why would they? The context may be environmental (Why is the moon so big? Well, things near the horizon tend to be further away) or it may come from the different sources of sensory information that arrive at the same time. This latter type of context provides the basis for the recent fascination with the multisensory nature of food, especially the findings that one sense can influence another, e.g. [1].
But this shouldn’t be surprising – the brain takes in and integrates whatever sources of information are needed to help us survive. In the food realm, this means identifying those things that are edible. Animal studies have even identified single nerve cells in the brain that receive information from touch, hearing and vision [2], because together such information might reliably tell us where something edible might be found.
But why do brains sometimes get it wrong? The answer is straightforward: if the information is incomplete or perhaps different senses contradict one another, the brain takes its best guess. A lot of the time, this guess relies on searching for, and identification of, patterns that are statistically more commonly experienced. Sometimes the best guess allows one sense to dominate others - visual dominance responsible for the illusion of the speaking ventriloquist’s dummy – because it is usually a more reliable source of information. At other times, such as when it’s easier to understand what someone is saying in a noisy environment if you can see their lips move, information from one sense enhances that from another.
This is exactly the same phenomenon that we see in foods when we find that an aroma can enhance the intensity of a taste. Beginning in the late 1980s, Frank and colleagues [3] explored the phenomenon of sweet-smelling odours. From these studies, two things stood out. The first of these was that such odours seemed to be mostly those that were repeatedly experience together with sweet tastes in foods. Secondly, a sweet smell would only enhance a sweet taste and not, for example, a salty taste. They noted that the odour and taste needed to share a common property – the sweetness – whether tasted or smelled.
A smell with a taste? A phantom aroma indeed! Except …. we now need to consider the one other source of information that the brain uses. This comes from …. wait for it …. Inside our heads! The fact that sweet aromas are those experienced previously with sweet tastes (and salty aromas with salty tastes, and so on) is the key. In integrating information about food, the brain only really cares about the fact that together the tastes, aromas and tactile qualities uniquely identify something useful to us. Ah, this flavour is sweet, say you (and your brain), and hence the food is good to eat. Because we respond to the overall flavour, and not which sense provides what information, the odour is not distinguished from the sweetness of the food and this is encoded in memory – subsequently sniffing the odour can then activate this memory and … hey presto! … a phantom aroma (except what The Atlantic Monthly presumably meant was a phantom taste).*
What this all means is that flavours are assembled from information that comes from the mouth and nose, together with other information resulting from our experiences with foods and extracted, consciously or not, from memory. In other words, flavours are at least partly cognitive. Some knowledge of this cognitive landscape, traditionally largely ignored by food scientists and flavour chemists, is crucial to understand perception, whether of foods or of anything else. Cognitive psychology – or as it is known now by those who want to ask the same questions using large, expensive machines, cognitive neuroscience – has provided models and techniques for studying memory, attention, decision making and, increasingly, emotions.
The crucial role that cognitive processes play helping us understand food perceptions and preferences extends beyond explanations of flavour, and odour/taste interactions. Consider the activity of wine tasting. In describing the wine, the taster selectively attends to some qualities (berry-like, tobacco notes) by somehow mentally extracting them from the complex mixture that is wine flavour. These notes can be weak or intense, but the only way of knowing this is by comparing in memory what is perceived to what is typical. Then there is the decision that might have to be made: is this a good wine or a wine typical of the region.
In fact, we don’t have to rely on expert wine tasters to illustrate our reliance on cognitive processes in tasting. Everyday evaluations of food carried out within the food industry or in food research environments illustrate the point equally well. Sensory scientists routinely administer tests to trained panelists or consumers to evaluate foods perceptions or preferences – what sensory qualities does a food possess, how strong are these qualities, are two products different, or perhaps which product is liked more. Alternatively, we can see the administration of sensory tests to panelists or preference tests to consumers as requests to pay attention to product attributes, make decisions about differences or preferences, to analyse complex flavours into their elements, remember previous product experiences for comparison, or to describe emotions arising from product experiences.
Even the way in which sensory tests are carried out is a function of what we know about cognitive biases. If you want people to attend to the overall flavour, don't ask them about different aspects of the flavour. In a group of products varying in intensity on an attribute, the first sample will be held in memory to act as the point of comparison for the other samples. Asking about the intensity of a single product will activate long-term memory for the intensity of what they usually consume. The answer to whether two products are the same or different will depend on the cognitive criterion for difference that the person adopts. And so on.
Cogito ergo … er, Gustavero? **
* Those wishing a more detailed account of this process should see one of the following reviews: [4-6]
** Even if you don’t know Latin, you should know Descartes – look it up!
1. Piqueras-Fiszman, B. and C. Spence, Sensory expectations based on product-extrinsic food cues: An interdisciplinary review of the empirical evidence and theoretical accounts. Food Qual Prefer, 2015. 40: 165-179.
2. Meredith, A. and B.E. Stein, Interactions among converging sensory inputs in the superior colliculus. Science, 1983. 221: 389-391.
3. Frank, R.A. and J. Byram, Taste-smell interactions are tastant and odorant dependent. Chemical Senses, 1988. 13(3): 445-455.
4. Prescott, J., Chemosensory learning and flavour: Perception, preference and intake. Physiol Behav, 2012. 107: 553-559.
5. Prescott, J. and R.J. Stevenson, Chemosensory Integration and the Perception of Flavor, in Handbook of Olfaction & Gustation: Modern Perspectives, R.L. Doty, Editor. 2015, John Wiley & Sons. 1008-1028.
6. Stevenson, R.J. and R.A. Boakes, Sweet and sour smells: the acquisition of taste-like qualities by odors, in Handbook of Multisensory Processes, G. Calvert, C.B. Spence, and B. Stein, Editors. 2004, MIT Press: Cambridge. 69-83.
