Have you ever touched a flavor?
The multisensory perception of taste
Starting when we are little children, the role of food in our lives is crucial. The act of sharing a meal is something so universally connecting that recipes shared within communities influence their culture. We create bonds over shared meals or drinks and can express our love through it. The combinations of ingredients and spices are endless, and the meals created by a good chef can almost feel like traveling with your taste buds. So how do we perceive this richness in flavors?
The gustatory system that encodes our perception of taste is well-studied: first, tastants are detected by taste receptor cells that are assembled into taste buds distributed among the elevations of the tongue mucosa (called papillae, which give the tongue its rough surface), but also the palate, larynx, pharynx, and epiglottis. A taste bud consists of about 100 taste receptor cells that project into a taste pore. A signal cascade is triggered once a tastant binds to the receptors on the microvilli of the taste receptor cell, resulting in the release of neurotransmitters. These cause the excitation of afferent nerve fibers, including parts of the facial, glossopharyngeal, and vagus nerves, which innervate taste buds on different parts of the inner mouth. Brain regions in the thalamus and brain stem integrate these signals before they are processed by the gustatory cortex—the brain region responsible for taste perception (Carleton et al., 2010). This enables us to distinguish five different taste qualities: bitter, salty, sour, sweet, and umami (umami describes the savory flavor caused by glutamate). However, consider the last time you ate your favorite dish or drank your favorite beverage: these five different taste qualities are hardly enough to describe the experience. It seems like there are more factors adding to the perception of taste, and many studies demonstrate the importance of our other senses in crafting what we call “taste.”
By thinking about your favorite food, you might start reminiscing about its smell. The link between taste and smell is well known and apparent in many situations. When our nose is blocked, we can experience a reduction or even a complete loss of taste. The first cup of coffee we ever drank smelled aromatic, while its actual flavor might have appeared shockingly bitter. For cheese, many people report the opposite effect; they might dislike the strong smell of a cheese, but end up loving the taste (Auvray & Spence, 2007; Rozin, 1982).
The connection between taste and smell is also studied in a more specific context: sweetness enhancement. It has been shown that certain smells can enhance the perceived sweetness of a food and that added sugar can enhance the perception of certain aromas. In one of the studies supporting these findings, participants had to chew on mint-flavored gum. Gum’s taste derives from the sugar in it, while menthol gives rise to the minty smell and the fresh feeling in the mouth. Initially, participants perceived the menthol more strongly when they started chewing and the sugar was released. The smell of menthol faded rapidly over 4-5 minutes and could only be brought back by the release of additional sugar—in other words, by adding a tastant that had no smell (Auvray & Spence, 2007; Davidson et al., 1999).
In the case of sweetness enhancement, it has been shown that our perception of taste is not only influenced by the olfactory system. A variety of different stimuli can influence how sweet we perceive the food and drinks in our mouth to be. One study served caramelized biscuits on two different plates: one plate was rough and had a grainy surface, while the other was smooth and had a shiny texture. Biscuits served on the smooth, shiny plate resulted in a sweeter and less crunchy rating than the ones from the rough plate. The authors of the study argue that this effect is caused by sensation transference: a crossmodal association between haptics and the taste, as well as the way the food feels in the mouth.
The sensation of our hands when touching the plate transfers to the taste and feel of the food (Wang et al, 2019; Biggs et al, 2016).
Beside smell and touch, what we hear while we eat also influences our sense of taste. This idea got the name ‘sonic seasoning’ and has become an increasingly popular topic in academic literature as well as in the popular press. It has been shown that auditory attributes are associated with basic tastes: sweet and sour tastes with high pitch sounds, and bitterness with low pitch. Crisinel and colleagues (2011) specifically composed a “sweet soundtrack” and “bitter soundtrack” for their participants to listen to while eating samples of bittersweet cinder toffee. When asked to rate the toffees on a sweet-bitter scale, the ratings were higher when the participants had listened to the sweet soundtrack (Crisinel et al., 2011).
Vision also influences how we perceive taste. We associate different colors of foods and beverages with specific basic tastes (Wang et al, 2019; Spence, 2015 for review). Color influences taste so strongly that the perceived taste can be altered by color stimuli. For instance, Morrot and colleagues (2001) showed that when white wine was colored red, participants used terms typically used to describe red wine. When the same white wine was not colored red, participants reverted to normal descriptions of white wine (Auvray and Spence, 2007; Morrot et al., 2001).
The food industry is interested in this research as it helps to determine how to get customers’ approval on new products that are introduced to the ever-growing market (Auvray & Spence, 2007). One area the industry is interested in is the color of food packaging, which plays a key role in capturing attention (Spence & Velasco, 2018) as well as in influencing the expectations and perceived taste of the product. Companies use color packaging to convey information about the sensory properties of their product, including its flavor. Furthermore, they prime more abstract brand attributes, such as health. While anecdotal evidence suggests that the consumer’s expected as well as perceived taste is affected by packaging color, scientific evidence remains sparse. More saturated food packaging leads to expectations of more intense sensory properties (Spence & Velasco, 2018). Tijssen and collegues (2017) tested the perceived taste of a low-sugar yoghurt under packaging conditions that varied in hue, saturation, and brightness. They found that packaging with low brightness and high saturation was perceived as tasting sweeter, creamier, and more flavorful. They also tested a sausage product and found a similar trend, alltough the results were not significant. So it seems that the packaging color can influence the perceived taste, but it does not have to, and the key factors deciding whether it does remain unclear (Wang et al, 2019; Spence & Velasco, 2018).
The research highlighted here shows how rich our perception of food is and how it can be influenced by other senses. In terms of integrating the information of various senses into a single perception, neuroimaging studies found the orbifrontal cortex to be involved in the process of combining different sensory modalities. The orbitofrontal cortex is a part of the prefrontal cortex and is also involved in the cognitive process of decision-making. Regarding which senses specifically interact, there might be various brain regions involved (Wang et al, 2019). For multisensory integration, it has been suggested that the central nervous system weights each modality as a function of its degree of certainty (for more information, see discussion of maximum likelihood function in Ernst & Banks, 2002).
According to this research, our brain mixes senses to (literally) make sense of our environment.
In our daily life, we encounter many situations in which our brain needs to integrate various senses to navigate through the outside world. Our sense of taste seems to be one of the most multisensory experiences we can encounter (to learn more, “The perfect meal: the multisensory science of food and dining” by Spencer & Piqueras-Fiszman provides an excellent summary). So, you might consider closing your eyes and savoring the contributions made by all of your senses during your next meal for added inspiration!
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Written by Lisa-Ruth Vial
Illustrated by Lisa-Ruth Vial
Edited by Zoe Guttman and Sean Noah
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References
Auvray, M., & Spence, C. (2008). The multisensory perception of flavor. Consciousness and cognition, 17(3), 1016-1031.
Biggs, L., Juravle, G., & Spence, C. (2016). Haptic exploration of plateware alters the perceived texture and taste of food. Food Quality and Preference, 50, 129-134.
Carleton, A., Accolla, R., & Simon, S. A. (2010). Coding in the mammalian gustatory system. Trends in neurosciences, 33(7), 326-334.
Crisinel, A. S., Cosser, S., King, S., Jones, R., Petrie, J., & Spence, C. (2012). A bittersweet symphony: Systematically modulating the taste of food by changing the sonic properties of the soundtrack playing in the background. Food quality and preference, 24(1), 201-204.
Davidson, J. M., Linforth, R. S., Hollowood, T. A., & Taylor, A. J. (1999). Effect of sucrose on the perceived flavor intensity of chewing gum. Journal of Agricultural and Food Chemistry, 47(10), 4336-4340.
Ernst, M. O., & Banks, M. S. (2002). Humans integrate visual and haptic information in a statistically optimal fashion. Nature, 415(6870), 429-433.
Morrot, G., Brochet, F., & Dubourdieu, D. (2001). The color of odors. Brain and language, 79(2), 309-320.
Rozin, P. (1982). ” Taste–smell confusions” and the duality of the olfactory sense. Perception & psychophysics.
Spence, C. (2015). On the psychological impact of food colour. Flavour, 4(1), 1-16.
Spence, C., & Piqueras-Fiszman, B. (2014). The perfect meal: the multisensory science of food and dining. John Wiley & Sons.
Spence, C., & Velasco, C. (2018). On the multiple effects of packaging colour on consumer behaviour and product experience in the ‘food and beverage’and ‘home and personal care’categories. Food quality and preference, 68, 226-237.
Wang, Q. J., Mielby, L. A., Junge, J. Y., Bertelsen, A. S., Kidmose, U., Spence, C., & Byrne, D. V. (2019). The role of intrinsic and extrinsic sensory factors in sweetness perception of food and beverages: A review. Foods, 8(6), 211.
