Leonardo doesn’t know what love feels like, and there’s no way to teach him because trying to describe that feeling to someone who has never experienced it is a bit like trying to describe the color green to someone who was born blind. We could tell Leonardo what causes the feeling (“It happens whenever I see Marilynn”), and we could tell him about its consequences (“I breathe hard and say goofy stuff”), but in the end, these descriptions would miss the point because the essential feature of love—like the essential feature of all emotions—is the experience. It feels like something to love, and what it feels like is love’s defining attribute (Heavey, Hurlburt, & Lefforge, 2012).

How can we study something whose defining attribute defies description? Although people can’t always say what an emotional experience feels like, they usually can say how similar or “close” one emotional experience is to another (“Love is more like happiness than like anger”). By asking people to rate the similarity of dozens of emotional experiences, psychologists have been able to use a technique known as multidimensional scaling to create a map of those experiences. The mathematics behind this technique is complex, but the logic is simple. Imagine that you had a list of the distances between a half-dozen U.S. cities and your job was to draw a map that reflected those distances. Whether you meant to or not, you would end up drawing a map of the United States because no other map would allow every city to be just the right distance from every other city (see FIGURE 8.1).

The same technique can be used to generate a map of the emotional landscape. If you had a list of the “distances” between a large number of emotional experiences (i.e., a list that showed how similar or “close” each was to the other) and tried to draw a map that reflected those distances, you would end up with a map like the one shown in FIGURE 8.2. What good would this map be? As it turns out, maps don’t just show where things are; they also reveal the dimensions on which they vary. For example, the map in FIGURE 8.2 reveals that emotional experiences vary on a dimension called valence (how positive or negative the experience is) and a dimension called arousal (how active or passive the experience is). Research shows that all emotional experiences can be described by their unique coordinates on this two-dimensional map (Russell, 1980; Watson & Tellegen, 1985; Yik, Russell, & Steiger, 2011).

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This map suggests that emotional experiences have two essential properties: they feel either good or bad, and they are associated with different degrees of bodily arousal. With these two facts in mind, we can define emotion as a positive or negative experience that is associated with a particular pattern of physiological activity. As you are about to see, the first step in understanding emotion involves understanding how the “experience” part and the “physiological activity” part of this definition are related.

You probably think that if you walked into your kitchen right now and saw a bear nosing through the cupboards, you would feel fear, your heart would start to pound, and the muscles in your legs would contract as you prepared to run. But in the late 19th century, William James suggested that the events might actually happen in the opposite order: First you’d see the bear, then your heart would start pounding and your leg muscles would contract, and then you would experience fear, which is simply your experience of your body’s response to the sight of the bear. Psychologist Carl Lange suggested something similar at about the same time, so the idea is now known as the James-Lange theory of emotion, which states that stimuli trigger activity in the body, which in turn produces emotional experiences in the brain. According to this theory, emotional experience is the consequence—not the cause—of our physiological reactions to objects and events in the world.

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James’s former student, Walter Cannon, didn’t like this idea very much, and so together with his student, Philip Bard, he proposed an alternative. The Cannon-Bard theory of emotion suggests that stimuli simultaneously trigger activity in the body and emotional experience in the brain (Bard, 1934; Cannon, 1929). Cannon and Bard claimed that their theory was better than the James–Lange theory for several reasons. First, emotions happen quickly even though the body often reacts slowly. For example, a blush is a bodily response to embarrassment that takes 15 to 30 seconds to occur, and yet, people feel embarrassed within seconds of noticing that, oh say, their pants have fallen off in public. How could the blush be the cause of the feeling if it happened after the feeling? Second, people often have trouble accurately detecting their own bodily responses, such as changes in their heart rates. If people can’t detect changes in their heart rates, then how can they experience those changes as an emotion? Third, environmental events, such as an increase in room temperature, cause the same bodily responses that an emotional stimulus does; so why don’t people feel afraid when they get a fever? Finally, Cannon and Bard argued that there simply aren’t enough unique patterns of bodily activity to account for all the unique emotional experiences people have. If many different emotional experiences are associated with the same pattern of bodily activity, then how could that pattern of activity be the sole determinant of the emotional experience?

These are all good questions, and about 30 years after Cannon and Bard asked them, psychologists Stanley Schachter and Jerome Singer supplied some answers (Schachter & Singer, 1962). Schachter and Singer thought that James and Lange were right to equate emotion with the perception of one’s bodily reactions, and that Cannon and Bard were right to note that there are not nearly enough distinct bodily reactions to account for the wide variety of emotions that human beings can experience. Their two-factor theory of emotion suggested that emotions are based on inferences about the causes of general physiological arousal (see FIGURE 8.3). According to this theory, when you see a bear in your kitchen, your heart begins to pound. Your brain notices both the pounding and the bear, puts two and two together, and interprets your bodily arousal as fear. According to the two-factor theory, people experience the same kind of bodily arousal in reaction to all emotional stimuli, but they interpret that arousal in different ways on different occasions. The feeling that your brain calls fear one day is exactly the same feeling that it might call excitement on another.

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How has the two-factor model fared in the last half century? One of the model’s claims has fared very well. For instance, participants in one study (Schachter & Singer, 1962) were injected with epinephrine, which causes physiological arousal, and then exposed to either a goofy or a nasty confederate. Just as the two-factor theory predicted, when the confederate acted goofy, participants concluded that they were feeling happy, but when the confederate acted nasty, participants concluded that they were feeling angry. Subsequent research has shown that when people are made to feel aroused—say, by having them ride an exercise bike in the laboratory—they subsequently find attractive people more attractive, annoying people more annoying, and funny cartoons funnier, as if they were interpreting their exercise-induced arousal as attraction, annoyance, or amusement (Byrne et al., 1975; Dutton & Aron, 1974; Zillmann, Katcher, & Milavsky, 1972). In fact, these effects occur even when people merely think they’re aroused—for example, when they hear an audiotape of a rapidly beating heart and are led to believe that the heartbeat they’re hearing is their own (Valins, 1966). It appears that the two-factor model is right when it suggests that people make inferences about the causes of their arousal and that those inferences influence their emotional experience (Lindquist & Barrett, 2008).

But research has not been so kind to the model’s claim that all emotional experiences are merely different interpretations of the same kind of bodily arousal. For example, researchers measured participants’ physiological reactions as they experienced six different emotions and found that anger, fear, and sadness each produced a higher heart rate than disgust, and that anger produced a larger increase in finger temperature than did fear (Ekman, Levenson, & Friesen, 1983; see FIGURE 8.4). These findings have been replicated across different age groups, professions, genders, and cultures (Levenson, Ekman, & Friesen, 1990; Levenson et al., 1991, 1992). In fact, some physiological responses seem unique to a single emotion. For example, a blush is the result of increased blood volume in the subcutaneous capillaries in the face, neck, and chest, and research suggests that people blush when they feel embarrassment but not when they feel any other emotion (Leary et al., 1992). Similarly, certain patterns of activity in the parasympathetic branch of the autonomic nervous system (which is responsible for slowing and calming rather than speeding and exciting) seem uniquely related to prosocial emotions such as compassion (Oately, Keltner, & Jenkins, 2006).

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Where does all this leave us? James and Lange were right when they suggested that the patterns of physiological response are not the same for all emotions. But Cannon and Bard were also right when they suggested that people are not perfectly sensitive to these patterns of response, which is why people must sometimes make inferences about what they are feeling. Our bodily activity and our mental activity are, it seems, both the causes and the consequences of our emotional experience.

In the late 1930s, psychologist Heinrich Klüver and physician Paul Bucy made an accidental discovery. A few days after performing brain surgery on a monkey named Aurora, they noticed that she was acting strangely. First, Aurora would eat just about anything and have sex with just about anyone—as though she could no longer distinguish between good and bad food, or between good and bad mates. Second, Aurora seemed absolutely fearless, remaining calm when she was handled by experimenters, and even when she was confronted by snakes (Klüver & Bucy, 1937). What had happened to her? As it turned out, during the surgery, Klüver and Bucy had accidentally damaged a structure in Aurora’s brain called the amygdala. Subsequent studies confirmed that the amygdala plays a special role in producing emotions such as fear. For example, people normally have superior memory for emotionally evocative words such as death or vomit, but people whose amygdalae are damaged (LaBar & Phelps, 1998) or who take drugs that temporarily impair neurotransmission in the amygdala (van Stegeren et al., 1998) do not (see FIGURE 8.5).

What exactly does the amygdala do? Is it some sort of “fear center”? Not exactly (Cunningham & Brosch, 2012). Before an animal can feel fear, its brain must first decide that there is something to be afraid of. This decision is called an appraisal, which is an evaluation of the emotion-relevant aspects of a stimulus (Arnold, 1960; Ellsworth & Scherer, 2003; Lazarus, 1984; Roseman, 1984; Roseman & Smith, 2001; Scherer, 1999, 2001). The amygdala is critical to making these appraisals. In essence, the amygdala is an extremely fast and sensitive threat detector (Whalen et al., 1998). Psychologist Joseph LeDoux (2000) found that information about a stimulus is transmitted through the brain simultaneously along two distinct routes. The thalamus is a kind of router that simultaneously sends information along a “fast pathway” (which goes directly from the thalamus to the amygdala) and a “slow pathway” (which goes from the thalamus to the cortex and then to the amygdala) (see FIGURE 8.6). This means that while the cortex is slowly using the information it received from the thalamus to conduct a full-scale investigation of the stimulus’s identity and importance, the amygdala has already received the information directly from the thalamus and is making one very fast and very simple decision: “Is this a threat?” If the amygdala’s answer to that question is yes, it initiates the neural processes that ultimately produce the bodily reactions and conscious experience that we call fear.

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The cortex takes longer to process its information than the amygdala does. But when it’s finished, it sends a signal to the amygdala telling it either to maintain the state of fear (“We’ve now analyzed all the data up here, and sure enough, that thing is a bear!”) or to decrease it (“Relax, it’s just some guy in a bear costume”). In a sense, the amygdala presses the emotional gas pedal and the cortex may or may not hit the brakes. When experimental subjects are instructed to experience emotions such as sadness, fear, and anger, they show increased activity in the amygdala and decreased activity in the cortex (Damasio et al., 2000), but when they are asked to inhibit these emotions, they show increased cortical activity and decreased amygdala activity (Ochsner et al., 2002). That’s why adults with cortical damage and children (whose cortices are not well developed) have difficulty inhibiting their emotions (Stuss & Benson, 1986).

The conclusion is clear: emotion is part of a primitive brain system that prepares us to react rapidly and on the basis of little information to things that are relevant to our survival and well-being. While our evolutionarily new cortex works to identify a stimulus and make a reasoned decision about what to do, our evolutionarily ancient amygdala makes a split-second decision about whether that stimulus is a threat. If that decision is a yes, the amygdala gets our hearts pounding, our legs running, and our butts the heck out of the kitchen.

It will not surprise you to learn that people would usually rather feel good than bad. Emotion regulation refers to the strategies people use to influence their own emotional experience. Ninety percent of people report attempting to regulate their emotional experience at least once a day (Gross, 1998), and describe more than a thousand different strategies for doing so (Parkinson & Totterdell, 1999). Some of these are behavioral strategies (e.g., avoiding situations that trigger unwanted emotions), some are cognitive strategies (e.g., recruiting memories that trigger the desired emotion; Webb, Miles, & Sheeran, 2012), and research shows that people don’t always know which of these strategies is most effective. For example, people tend to think that suppression, which involves inhibiting the outward signs of an emotion, is generally an effective strategy, but by and large, it isn’t (Gross, 2002). Conversely, people tend to think that affect labeling, which involves putting one’s feelings into words, will have little impact on their emotions, when in fact, it is actually an effective way to reduce the intensity of an emotional state (Lieberman et al., 2011).

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One of the best strategies for emotion regulation is reappraisal, which involves changing one’s emotional experience by changing the way one thinks about the emotion-eliciting stimulus (Ochsner et al., 2009). For example, in one study, participants’ brains were scanned as they saw photos that induced negative emotions, such as a photo of a woman crying during a funeral. Some participants were then asked to reappraise the picture, for example, by imagining that the woman in the photo was at a wedding rather than a funeral. The results showed that when participants initially saw the photo, their amygdalae became active. But as they reappraised the picture, several key areas of the cortex became active, and moments later, their amygdalae were deactivated (Ochsner et al., 2002). In other words, participants were able to turn down the activity of their own amygdalae simply by thinking about the photo in a different way.

When it comes to reappraisal, some people do it better than others (Malooly, Genet, & Siemer, 2013), and those who do it best tend to be the most mentally and physically healthy (Davidson, Putnam, & Larson, 2000; Gross & Munoz, 1995). Indeed, as you will learn in the Stress and Health chapter, therapists often attempt to alleviate depression and distress by teaching people how to reappraise key events in their lives (Jamieson, Mendes, & Nock, 2013). About two thousand years ago, the Roman philosopher and emperor Marcus Aurelius wrote: “If you are distressed by anything external, the pain is not due to the thing itself, but to your estimate of it; and this you have the power to revoke at any moment.” Modern science suggests that he was right.