Victory is sweet. Defeat is bitter. When the salesman tried to trick you into paying too much for a used car, the experience left a bad taste in your mouth. When your relationship broke up and your ex said, “I never really cared about you anyway,” it was just sour grapes. The psychological experience of taste, which is produced by the gustatory system, is so central to human experience that we use tastes as metaphors for discussing life’s ups and downs.

Taste, in fact, may be necessary to life itself. People who lose their sense of taste have trouble getting themselves to eat, despite needing nutrition to live. One such person, who lost gustatory ability after radiation therapy for cancer, said that, without taste, being served a meal is like “being presented with a piled-high plate of charcoal biscuits by a menacing giant who says ‘Eat it up, it will do you good.’” As one doctor described such a loss:

If, by a mighty effort, the “cinders” are forced down with copious fluid, the consequences are acute indigestion or vomiting. … [I]f there is anything objectionable to feel (such as gristle in [meat]) a sort of panic nausea may be the next reaction.… The patient is not hungry anyway, and it is easier to starve.

—MacCarthy-Leventhal (1959, p. 1138)

We need tastes. The gustatory system gives them to us by responding to the chemical properties of foods and sending these responses to the brain.

When you try different foods, your perceptions of them differ in two ways:

194

Let’s review these two aspects of taste perception and then discuss flavor, an experience that combines taste and smell.

TASTE QUALITIES. Humans perceive five distinct taste qualities. Even complex food tastes—the robust flavors of a spicy Chinese stir-fry or the subtlety of French haute cuisine—are blends of these five simple, basic types of taste (Breslin & Spector, 2008):

DIMENSIONS OF GUSTATORY EXPERIENCE. All salty tastes are not the same. Neither are all sour tastes, nor gustatory experiences of the other taste categories. Tastes also differ along a number of taste dimensions.

Four taste dimensions describe variations in gustatory experience (Figure 5.41). Onset/aftertaste describes taste experience across time. For example, some tastes linger, whereas others “vanish” soon after a food is swallowed. Intensity describes the strength of the gustatory experience. Two foods might both be sour, but one could have a much greater intensity of sourness than the other. Hedonics refers to how much you like the taste. Hedonics and intensity are often related; you might like salty potato chips—unless they’re too salty (i.e., unless the saltiness is too intense). Finally, localization is perception of where within the mouth a taste is experienced. The gustatory system’s taste receptors provide information about whether a taste occurs on the left or right side of the tongue (Shikata, McMahon, & Breslin, 2000).

195

FLAVOR. We have been considering perceptual systems one at a time, but sometimes they work together. A prime case of this is the perception of food.

Imagine that you’re trying to guess the seasonings in some food (e.g., “What’s in that tomato sauce?”). Some of the perceptual information you gather comes from taste. But, some of it comes from smell—that is, from the olfactory system. The combination of two perceptual systems—gustation and olfaction—contributes to the overall perceptual experience of the food, or its flavor.

In the experience of flavor, your perceptual systems integrate information about taste and smell to produce a coherent perceptual experience (Auvray & Spence, 2008). You don’t have two separate experiences of a food product, one olfactory and one gustatory (“Hmm, I smell some garlic somewhere”; “Oh, and I taste some garlic in my mouth”). You have one integrated perceptual experience of the food (“There’s garlic in that soup”).

Both everyday observation and scientific findings show how smell and taste interact. If you have a stuffy nose from a cold, or just hold your nose when eating, you cannot perceive the flavor of food as keenly as normal. Research shows that smells influence tastes. For example, a food’s odor can influence how sweet it tastes (Auvray & Spence, 2008).

SUPERTASTERS. Not everyone’s experience of foods is the same. Some of us are supertasters: people who have greater sensitivity to tastes than others.

Supertasters were discovered in research by psychologist Linda Bartoshuk and her colleagues (Bartoshuk, 2000). In their studies, participants were asked to rate, on a measurement scale, the intensity of their experiences when tasting various substances. A subset of individuals provided extremely high ratings of intensity. There were two possible interpretations of this result: (1) These people were more sensitive to tastes than others; or (2) they were no more sensitive to tastes than others, but merely tended to make more extreme ratings when filling out measurement scales during psychology experiments.

To determine which interpretation was correct, the researchers devised a clever new measurement procedure (Bohannon, 2010). They asked people to rate the most intense sensation (e.g., an intense pain) they ever experienced, and then to rate the intensity of taste experiences. The use of two ratings allowed the researchers to control for people’s general tendency to make low- or high-intensity ratings when completing scales. The results confirmed that supertasters were “super”: They made uniquely high ratings of sensory intensity specifically when tasting food.

196

In taste perception, connecting psychological phenomena to biological mechanisms is straightforward. The biology of gustation directly explains many of the psychological phenomena you just learned about.

The first step in getting gustatory information from mouth to brain involves taste receptors, which are cells that are stimulated by chemical substances in food. When stimulated, taste receptors release neurotransmitters that begin the process of transmitting gustatory information to the brain (Smith & Margolskee, 2001). Taste receptors are bundled together in taste buds, each of which contains about 50 to 100 receptor cells. Taste buds are found primarily on the tongue, but also on the roof of the mouth and throat (Breslin & Spector, 2008).

Evidence indicates that there are five types of taste receptors. The good news—if you’re trying to connect psychological and biological levels of analysis—is that these receptor types correspond to the five taste qualities we just reviewed. Different types of receptor cells are “tuned” to detect each of the five taste qualities: sweet, salty, bitter, sour, and umami (Chandrashekar et al., 2006; Figure 5.42). Contrary to what was once thought, receptors of each type are found in multiple areas of the tongue; it is not the case that any one large region of the tongue is responsive only to one taste quality.

Biological analyses of the gustatory system also reveal individual differences. Supertasters have more of the bumps on the tongue that contain taste buds. They thus have more taste receptors and superior gustatory perception (Figure 5.43).

Signals from taste receptors travel along neural pathways to a lower region of the brain known as the brain stem (see Chapter 3), and then to an upper region known as the gustatory cortex. The gustatory cortex, a region in the brain’s parietal lobe, completes the processing of perceptual signals involving taste (Kobayakawa et al., 2005). It is highly connected to other regions of the brain, which means that taste perception is affected by other sensory inputs and the overall state of the body (de Araujo & Simon, 2009). Scientists are just starting to learn how information about taste is represented in this brain region (see This Just In).

197

THIS JUST IN