How Has Personality Been Studied?
The initial section of the chapter reviews what personality is and the four traditional approaches for studying it. Although researchers have disagreed about specific aspects, there is relative agreement that the term personality refers to a person's characteristics, emotional responses, thoughts, and behaviors that are relatively stable over time and across circumstances. Psychodynamic theorists, beginning with Freud, have proposed that unconscious forces influence behavior. Freud developed a topographical model of the mind in which there are three levels of mental awareness: conscious, preconscious, and unconscious. Freud described how thinking and behavior develop in five psychosexual stages (oral, anal, phallic, latency, genital ) based on children's interactions with their parents. Finally, he proposed a structural model of personality in which three dynamic processes (id, ego, superegostruggle to meet basic needs in the context of interaction with the social environment. Despite the many criticisms of Freudian theory, it served as a springboard for much of the theorizing and research of the past century.

Humanistic personality theorists objected to the determinism of Freudian (and later behavioral) models. They emphasized personal experience, or phenomenology, and the fulfillment of human potential (self-actualization). Recently, this has led to the positive psychology movement and the scientific investigation of the positive aspects of humanity. Trait theorists propose that individuals differ on broad personality dispositions. Factor analysis of these traits has led to a number of different solutions, but in the last 20 years many personality psychologists have endorsed the five-factor theory of personality. The Big Five, as they are known, are extraversion, neuroticism, conscientiousness, agreeableness, and openness to experience. Finally, cognitive-social theories of personality have integrated the findings of learning theory with the idea that beliefs, expectancies, and interpretations also influence the exhibition of behavior.

Table 15.1: Traditional Approaches to the Study of Personality
Theoretical Approach	View of Personality
Psychodynamic	result of unconscious conflicts, usually developed in childhood
Humanistic	result of striving for fullest human potential (self-actualization)
Trait	reflected in variations of broad human dispositions
Cognitive-social	integration of learning history and cognitive expectancies and beliefs

How Is Personality Assessed and What Does It Predict?
The next section of the chapter deals with the assessment of personality. Idiographic approaches to understanding personality address individuals and the characteristics that make them unique. Common techniques in this approach are case studies and psychobiography. Nomothetic approaches focus on characteristics that are common among all people but for which individuals vary. Traditionally, assessment tools have been divided into projective and objective measures. Projective measures, such as inkblots and the Thematic Apperception Test, are based on psychodynamic theory. That is, it is hypothesized if you are presented with an ambiguous stimulus, you will project your unconscious conflicts onto that stimulus. Recent developments in these techniques have been more empirically based. Objective measures are more direct and usually consist of behavioral observations or self-report questionnaires (e.g., NEO personality inventory).

Walter Mischel initiated a turning point in personality study with his 1968 proclamation that the traits assessed by such measures did a poor job of predicting behavior. His theory of situationism suggested that the interpersonal environment had a much greater influence on behavior, which calls into question whether the construct of personality even exists. The result of this work led to much research and today's idea of interactionism, which maintains that behavior is the result of both broad dispositions and the unique situation.

What Is the Biological Basis of Personality?
Research into the biological basis of personality has done much to illuminate many of the classic questions of personality (e.g., Does personality exist? Can personality change?). It is now evident that personality is strongly rooted in neurophysiology, and roughly half the variance in personality traits is accounted for by genetic influences. Biological differences in personality, referred to as temperaments, are evident in very young children and persist throughout the life span. In direct contrast to the ideas of Freud, Stella Chess and Alexander Thomas found that many children can be divided into one of three temperaments (easy, difficult, slow to warm up), regardless of parental upbringing. The temperamental trait of introversion/extraversion has been strongly linked to neurophysiology. Introverts have an active behavioral inhibition system that leads them to avoid social situations in which they anticipate possible negative outcomes. Extraverts have a stronger behavioral approach system and are influenced more by the possibility of rewards than punishments. The results of these investigations suggest that people are different because of differing physiology. These preferences also likely reflect what has been adaptive for us over the course of human evolution.

Can Personality Change?
Sigmund Freud proposed that the personality is basically fixed by the age of 5. This infuriated people in Western cultures, because it contradicted the possibility for change and improvement that is part of our mythology. Research in temperament suggests that these early tendencies do play a pervasive and influential role in adulthood. A meta-analysis of 150 studies on personality change indicated that there is a possibility for change in childhood, but personality becomes very stable by middle age. Part of the debate concerns the definition of personality. Our basic tendencies, which are highly determined by biological processes, tend to be very stable. Our characteristic adaptations may vary in novel situations, but it is argued that our core dispositions do not change. Still, we maintain the possibility of a quantum change or personality transformation, but this results only from an extreme negative affect (hitting rock bottom) and/or a trigger event. A final finding that certain personality traits are strongly related to neurochemistry (e.g., hostility and serotonin) and can be manipulated leads to a host of ethical questions. If thousands of years of human evolution have led us to vary on the trait of sociability, should we take a pill that instantly would make us more sociable? Is it adaptive to make everyone more cooperative and less hostile?