Flavor

All foods and beverages stimulate multiple, physiologically distinct, sensory systems. Information from volatile chemicals reaches the olfactory receptors deep inside the nose either via sniffing (orthonasally), or via the nasopharynx once the food is in the mouth (retronasally). With either route, information reaches the olfactory bulb via cranial nerve (CN) I. Molecules from soluble compounds in foods—including (but not limited to) carbohydrates, salts, acids, amino acids, and probably fatty acids—bind with taste receptors, most of which are embedded within raised structures (papillae) on the dorsal and lateral surfaces of the tongue. For taste information, these structures are innervated primarily by CN VII (chorda tympani) and CN IX (glossopharyngeal). Foods also stimulate nerve fibers responsive to touch and temperature, and—in the case of hot spices—those that mediate pain, particularly via branches of CN V (trigeminal) located throughout the mouth, tongue, and nose. Unique receptor mechanisms and specific nerve pathways from the periphery to discrete areas at each level of the brain distinguish these sensory modalities, in the same way that vision and hearing are distinct from one another.

In everyday considerations of food or beverage flavors, the word taste is often used, as in an orange taste. However, this usage not only covers actual tastes, typically sweetness and sourness, but implicitly also the olfactory quality, orange, as it is perceived retronasally. Given the multisensory nature of eating and drinking experiences, flavor is most properly seen as an aggregation of odor, taste, tactile, and, under some circumstances, visual properties. However, these apparently distinct sensory modalities are seldom independent. What we respond to, perceptually and hedonically, during food consumption is not a collection of discrete sensory signals, but rather an overall percept of a flavor. Thus, orange juice flavor appears somehow more than the sum of its parts: the odor of orange, the tastes of sugar and citric acid, and a variety of tactile and temperature sensations. This is rather in contrast to multisensory interactions involving other sensory systems. For example, we automatically link the visual image of a bird and its song because they arise from the same location, but we are nevertheless conscious that these aspects are distinct in sensory terms. In contrast, flavor components seem more highly integrated. As such, the study of flavor perception is interesting both as an example of commonplace multisensory interaction and integration and for what this integration of the different components of flavor—and in particular, odors and tastes—reveals about the biology and psychology of food perceptions.

One implication of the interchangeability of flavor and taste in common usage is that we routinely fail to make a distinction between olfactory and taste qualities within flavors. In turn, this is one manifestation of the fact that, during normal food consumption, these flavor elements are highly integrated. In studies of other sensory systems—vision and audition, for example—such cross-modal integration is inferred from the influence of one modality on another. Commonly, this is an enhanced (sometimes supra-additive) response to information from one sensory system resulting from concurrent input from another modality. For example, in a crowded room, speech comprehension is improved if we see the speaker's lip movements. There is similarly evidence that tastes and odors, when [Page 462]encoded together as a flavor, interact to modify one another. This entry discusses various aspects of flavor, focusing on multisensory, cross-modal, and attentional processes and neural representation.

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