Premed · Premed · Introductory Psychology
Lecture 15: Motivation and Emotion
Introductory Psychology
Learning Objectives
By the end of this lecture, students will be able to:
- Define motivation and compare the major theories of motivation
- Describe the biological and psychological factors regulating hunger and eating
- Explain the major theories of emotion and the role of physiological arousal
- Identify the basic emotions and their adaptive functions
- Discuss the nonverbal communication of emotion and cultural differences in emotional expression
Lecture Content
I. Motivation: Theories and Concepts
Motivation refers to a need or desire that energizes and directs behavior toward a goal. Several theoretical perspectives attempt to explain what drives human action. Instinct theory, rooted in evolutionary thinking, holds that behavior is driven by innate, fixed patterns. While this perspective explains some animal behaviors, it is limited in accounting for the full complexity of human motivation.
Drive-reduction theory, developed by Clark Hull, proposes that physiological needs create aroused states called drives, which motivate behavior aimed at satisfying those needs. The body's tendency to maintain a stable internal state is called homeostasis, and drives arise when homeostasis is disrupted. The limitation of this theory is that it cannot explain behaviors that increase rather than reduce arousal, such as thrill-seeking or curiosity.
Arousal theory addresses this gap by proposing that we seek an optimal level of arousal — not too high, not too low. The Yerkes-Dodson law describes the relationship between arousal and performance as an inverted U: performance is best at moderate arousal, with simple tasks having a higher optimal arousal level and complex tasks requiring a lower one. Individual differences in sensation seeking, as described by Zuckerman, reflect variation in the need for novel, varied, and intense experiences.
Incentive theory shifts the focus from internal pushes to external pulls, proposing that behavior is motivated by environmental stimuli (incentives) rather than internal drives alone. In practice, both drives and incentives work together. Maslow's hierarchy of needs organizes motivation into five levels, from physiological needs at the base through safety, belongingness, esteem, and finally self-actualization at the peak. Lower needs must be at least partially satisfied before higher needs become motivating, though this rigid hierarchy has not been well supported empirically; people can and do pursue higher needs before lower ones are fully met, and the model carries a Western cultural bias.
Self-determination theory, developed by Deci and Ryan, identifies three innate psychological needs — autonomy, competence, and relatedness — that, when satisfied, sustain intrinsic motivation. When these needs are thwarted, or when extrinsic rewards are applied to already intrinsically motivated activities, the result can be the overjustification effect: a decrease in intrinsic motivation.
II. Hunger and Eating
The regulation of hunger involves a complex interplay of biological factors. Stomach contractions signal hunger, as Cannon and Washburn demonstrated in 1912, though hunger persists even in the absence of a stomach. Drops in blood glucose trigger hunger (the glucostatic hypothesis). The hypothalamus plays a central role: stimulation of the lateral hypothalamus triggers eating, while its lesioning causes aphagia (failure to eat); stimulation of the ventromedial hypothalamus suppresses eating, while its lesioning causes hyperphagia (overeating). The arcuate nucleus integrates hormonal signals, and modern understanding recognizes that the system is far more complex than a simple dual-center model.
Several hormones regulate appetite. Ghrelin, released by the stomach, signals hunger. Leptin, released by fat cells, signals satiety and reduces appetite. Insulin regulates blood glucose and influences fat storage and hunger. PYY, released by the intestines after eating, signals fullness. Orexin, produced in the hypothalamus, stimulates both appetite and wakefulness.
Set point theory proposes that the body defends a genetically determined weight through metabolic adjustments, while settling point theory suggests that weight stabilizes at a point determined by the interaction of biology and environment. The fact that basal metabolic rate decreases when food intake is restricted helps explain why dieting is so difficult.
Psychological and social factors also shape eating behavior. Unit bias leads people to eat more when given larger portions. Social facilitation increases consumption in the presence of others. Sensory-specific satiety means that variety increases how much people eat. Stress eating and cultural norms further influence dietary patterns.
Eating disorders represent extreme dysregulation of eating behavior. Anorexia nervosa involves severe food restriction, intense fear of weight gain, and distorted body image. Bulimia nervosa is characterized by cycles of binge eating followed by compensatory behaviors such as purging, fasting, or excessive exercise. Binge-eating disorder involves recurrent binges without compensatory behaviors. Risk factors for eating disorders include genetics, perfectionism, low self-esteem, cultural emphasis on thinness, and family dynamics. While most common in adolescent and young adult females, eating disorders occur across all demographic groups.
III. Theories of Emotion
Emotion is a complex state involving physiological arousal, cognitive appraisal, expressive behavior, and conscious experience. Several competing theories address how these components relate to one another.
The James-Lange theory proposes that we experience emotion because we perceive our bodily responses — in other words, "we feel afraid because we run," not "we run because we are afraid." Supporting evidence comes from the facial feedback hypothesis and from research showing that spinal cord injuries can reduce emotional intensity. Critics point out that similar physiological responses accompany different emotions and that arousal may be too slow to precede emotional experience.
The Cannon-Bard theory argues that physiological arousal and conscious emotion occur simultaneously and independently, both triggered by the thalamus. Critics note that arousal and emotion are not truly independent; arousal does influence the quality of emotional experience.
Schachter and Singer's two-factor theory proposes that emotion requires both physiological arousal and a cognitive label for that arousal based on the situational context. The famous bridge study by Dutton and Aron demonstrated this principle: men on a frightening suspension bridge misattributed their physiological arousal to attraction toward a female interviewer. The related concept of excitation transfer explains how residual arousal from one situation can intensify emotional responses to an entirely different situation.
Lazarus's cognitive appraisal theory holds that cognition precedes and determines emotional response. How we interpret an event — through primary appraisal ("Is this threatening or beneficial?") and secondary appraisal ("Can I cope?") — determines which emotion we experience. Zajonc offered a counterpoint, arguing that some emotional reactions occur instantly, without conscious cognitive processing. His research on the mere exposure effect and on subliminal emotional stimuli suggests that emotion and cognition are partially independent systems.
<image>A comparison diagram of four major theories of emotion. Each theory is shown as a flow diagram. Panel A: James-Lange — Stimulus (bear) → Physiological response (heart racing, running) → Conscious emotion (fear). Panel B: Cannon-Bard — Stimulus (bear) → simultaneous branching to Physiological response AND Conscious emotion. Panel C: Schachter-Singer — Stimulus (bear) → Physiological arousal + Cognitive label ("I'm scared because of the bear") → Conscious emotion (fear). Panel D: Lazarus — Stimulus (bear) → Cognitive appraisal ("That bear is dangerous") → Physiological response + Conscious emotion. Arrows clearly show the causal sequence in each model.</image>
IV. Basic Emotions and Their Functions
Paul Ekman's cross-cultural research identified six universal basic emotions — happiness, sadness, anger, fear, disgust, and surprise — with contempt and others added later. The facial expressions associated with these emotions are recognized across diverse cultures, including isolated pre-literate societies, suggesting a biological basis. Some researchers argue, however, that certain emotions may be partly culturally constructed, and the precise classification remains debated.
Each basic emotion serves adaptive functions. Fear mobilizes escape or avoidance through the fight-or-flight response. Anger energizes responses to overcome obstacles or perceived threats. Disgust promotes avoidance of contamination and pathogens. Happiness broadens thinking and builds social connections, consistent with Fredrickson's broaden-and-build theory. Sadness signals a need for social support and promotes reflection. Surprise orients attention toward unexpected events.
V. Emotional Expression
Ekman and Friesen developed the Facial Action Coding System (FACS), which catalogs the facial muscle movements underlying emotional expressions. A genuine (Duchenne) smile involves both the zygomatic major muscle (raising the mouth corners) and the orbicularis oculi muscle (crinkling the eyes), whereas a social or polite (non-Duchenne) smile involves only the mouth. The facial feedback hypothesis proposes that facial expressions can influence emotional experience, not merely reflect it. The classic study by Strack and colleagues (1988), in which holding a pen in the teeth (simulating a smile) increased humor ratings, has produced mixed results in replication attempts.
Gender differences in emotional expression are well documented: women tend to be more emotionally expressive and better at reading nonverbal emotional cues, though men and women report similar levels of emotional intensity. Cultural display rules — norms governing when and how emotions should be expressed — also shape emotional behavior. Individualistic cultures tend to encourage open expression of personal emotions, while collectivistic cultures emphasize suppressing emotions that might disrupt group harmony.
Nonverbal communication includes body language, gestures, tone of voice, personal space, and touch. Much emotional communication is nonverbal. Mehrabian's widely cited (and widely misapplied) finding that emotional communication is roughly 55% facial, 38% vocal tone, and 7% verbal applies specifically to ambiguous situations and should not be generalized to all forms of communication.
<image>A grid of six faces showing the universally recognized basic emotions identified by Ekman. Panel A: Happiness — raised cheeks, lip corners pulled up, crow's feet around eyes (Duchenne markers labeled). Panel B: Sadness — inner brow raise, lip corners pulled down. Panel C: Anger — brows lowered and drawn together, lips pressed. Panel D: Fear — brows raised and drawn together, eyes widened, mouth open. Panel E: Disgust — nose wrinkled, upper lip raised. Panel F: Surprise — brows raised, eyes wide, jaw dropped. Each face has key facial muscles labeled (zygomatic major, orbicularis oculi, corrugator supercilii, etc.).</image>
