Introduction
A broad definition of personality typically includes the dimensions of stability, determinism, and uniqueness. That is, personality changes little over time, is determined by internal processes and external factors, and reflects an individual’s distinctive qualities. Personality also can be thought of as unique, relatively stable patterns of behavior, multiply determined over the course of an individual’s life. There are many theories for understanding the development of these patterns of behavior.
Twin studies
have provided evidence that biological factors help to shape personality; such studies support Hans Eysenck’s theory that personality is inherited. The psychodynamic perspective holds that personality is determined primarily by early childhood experiences. Some of the most influential contributions to this perspective came from Sigmund Freud. He argued that unconscious forces govern behavior and that childhood experiences strongly shape adult personality via coping strategies people use to deal with sexual urges. B. F. Skinner, founder of modern behavioral psychology, assumed that personality (or behavior) is determined solely by environmental factors. More specifically, he believed that consequences of behavior are instrumental in the development of unique, relatively stable patterns of behavior in individuals. According to Albert Bandura’s social learning theory
, models have a great impact on personality development. That is, patterns of behavior in individuals are influenced by their observations of others. Finally, the humanistic perspective of Carl R. Rogers suggests that personality is largely determined by the individual’s unique perception of reality in comparison to his or her self-concept.
Personality Assessment
Assessment of personality can be accomplished from three domains: subjective experience, behavior, and physiology. Traditional means for assessing personality have included objective and projective paper-and-pencil or interview measurements that tap the domain of subjective experience. Behavioral assessment techniques such as direct observation of behavior, self-monitoring (having the individual record occurrences of his or her own behavior), self-report questionnaires, role-play scenarios, and behavioral avoidance tests (systematic, controlled determination of how close an individual can approach a feared object or situation) tap the domains of subjective experience and objective behavior. These techniques have been used in clinical settings to aid in the diagnosis and treatment of deviant or abnormal behavior patterns.
Although psychophysiological measurement of personality has not gained popular use in clinical settings, it complements the techniques mentioned above and contributes to understanding the nature and development of psychological and physical disorders. Just as patterns of responding on traditional personality tests can indicate the possibility of aberrant behavior, so too can tests of physiological patterns. Typical measures taken during this type of assessment include heart rate, blood pressure, muscle tension (measured via electromyography), brain-wave activity (measured via electroencephalography), skin temperature, and palmar sweat gland or electrodermal activity. These measures of physiological activity are sensitive to “emotional” responses to various stimuli and have been instrumental in clarifying the nature of certain psychological and physical conditions. One of the fundamental assumptions of psychophysiology is that the responses of the body can help reveal the mechanisms underlying human behavior and personality.
Physiological responsivity can be assessed in a number of different ways. Two primary methodologies are used in the study of the relations between personality and physiology. The first method simply looks at resting or baseline differences of various physiological measures across individuals who either possess or do not possess the personality characteristic of interest. The second method also assesses individuals with or without the characteristic of interest but does this under specific stimulus or situational conditions rather than during rest. This is often referred to as measuring reactivity to the stimulus or situational condition. Resting physiological measures are referred to as tonic activity (activity evident in the absence of any known stimulus event). It is postulated that tonic activity is relatively enduring and stable within the individual while at rest, although it can be influenced by external factors. It is both of interest in its own right and important in determining the magnitude of response to a stimulus. On the other hand, phasic activity is a discrete response to a specific stimulus. This type of activity is suspected to be influenced to a much greater extent by external factors and tends to be less stable than tonic activity. Both types of activity, tonic and phasic, are important in the study of personality and physiology.
Standard laboratory procedures are typically employed to investigate tonic activity and phasic responses to environmental stimuli. For example, a typical assessment incorporating both methodologies might include the following phases: a five-minute baseline to collect resting physiological measures, a five-minute presentation of a task or other stimulus suspected to differentiate individuals in each group based on their physiological response or change from baseline, and a five-minute recovery to assess the nature and rate of physiological recovery from the task or stimulus condition. Investigations focusing on the last phase attempt to understand variations in recovery as a response pattern in certain individuals. For example, highly anxious individuals tend to take much longer to recover physiologically from stimulus presentations that influence heart rate and electrodermal activity than individuals who report low levels of anxiety.
Studies of physiological habituation
—the decline or disappearance of response to a discrete stimulus—also have been used to investigate personality differences. Physiological responses to a standard tone, for example, eventually disappear with repeated presentations of the tone. The rate at which they disappear varies across individuals; the disappearance generally takes longer in individuals who tend to be anxious. Thus, individuals who tend to have anxious traits may be more physiologically responsive, recover from the response less rapidly, and habituate to repeated stimulation more slowly than those who tend to be less anxious. Such physiological differences may be an important characteristic that determines anxious behavior or results from subjective feelings of anxiousness.
Relationship to Physiology and Health
Research has demonstrated that there is considerable variability across individuals in their physiological response patterns, both at rest and in response to various situational stimuli or laboratory manipulations. Evidence indicates that part of this variability across individuals may in some cases be attributable to certain personality traits or characteristic patterns of behavior. Furthermore, research suggests that these personality traits may also be related to the development of psychological or physical disorders. Although the causal links are not well understood, a growing body of research points to relations among personality, physiological measures, and psychopathology/health.
Examples of these relationships are evident in the field of psychopathology, or the study of abnormal behavior. Eysenck proposed that the general characteristics of introversion and extroversion lead individuals to interact very differently with their environment. Some psychophysiological studies support this notion and suggest that the behaviors characteristic of these traits may be driven by physiological differences. Anxiety sensitivity and locus of control are two personality traits that some suggest are related to the development of anxiety disorders and depression, respectively. To varying degrees, anxiety disorders and depression have been investigated in the psychophysiology laboratory and have been found to differentiate individuals with high and low levels of the personality trait, based on their physiological responses.
Introversion describes the tendency to minimize interaction with the environment; extroversion is characterized by the opposite behaviors, or the tendency to interact more with the environment. Eysenck proposed that such traits reflect physiological differences that are genetically determined and reflected in the individual’s physiology. Introverted individuals are thought to be chronically physiologically hyperaroused and thus to seek to minimize their arousal by minimizing external stimulation. Extroverted individuals are believed to be chronically physiologically underaroused and to seek a more optimal level of arousal through increased environmental stimulation. It should be easy to confirm or disprove such a theory with psychophysiological studies of resting physiological activity in introverts and extroverts. Electroencephalograph (EEG) studies have produced contradictory evidence about the validity of Eysenck’s theory, however; problems in EEG methodology, experimental design, and measurement of the traits themselves have led to considerable confusion about whether the traits actually do have a physiological basis.
Anxiety Sensitivity
Anxiety sensitivity describes the tendency for individuals to fear sensations they associate with anxiety because of beliefs that anxiety may result in harmful consequences. Research in the development and assessment of this construct was pioneered by Steven Reiss and his associates in the late 1980s. They developed a sixteen-item questionnaire, the Anxiety Sensitivity Index (ASI), to measure anxiety sensitivity and found it to be both reliable and valid. Anxiety sensitivity has been most closely related to panic disorder, an anxiety disorder characterized by frequent, incapacitating episodes of extreme fear or discomfort. In fact, as a group, individuals with panic disorder score higher on the ASI than individuals with any other anxiety disorder. Furthermore, some researchers have demonstrated that individuals scoring high on the ASI are five times more likely to develop an anxiety disorder after a three-year follow-up.
Research investigating responses to arithmetic, caffeine, and hyperventilation challenges in the laboratory has demonstrated that individual differences in anxiety sensitivity levels are probably more closely related to the subjective experience of anxiousness than to actual physiological changes. Individuals high and low on anxiety sensitivity, however, have exhibited differential heart-rate reactivity to a mental arithmetic stressor. That is, individuals high on anxiety sensitivity show a greater acceleration in heart rate than individuals low on anxiety sensitivity when engaging in an arithmetic challenge. Individuals scoring high on the ASI also more accurately perceive changes in their physiology when compared with their low-scoring counterparts. Such heightened reactivity and sensitivity to physiological change may partially explain how anxiety sensitivity influences the development of anxiety disorders. Individuals high in anxiety sensitivity may be more reactive to environmental threat; therefore, their increased sensitivity may have a physiological basis. They also may be more likely to detect changes in their physiology, which they are then more likely to attribute to threat or danger.
On a more general note, cardiovascular and electrodermal measures can differentiate between anxiety patients and other people at rest. The differences become greater under conditions of stimulation. Delayed habituation rates in anxiety patients are also part of the pattern of physiological overarousal typically seen in individuals with heightened anxiety. Indeed, heightened physiological arousal is one of the hallmark characteristics of anxiety.
Locus of Control
Locus of control, made popular by Julian Rotter in the 1960s, refers to individuals’ perceptions of whether they have control over what happens to them across situations. This personality construct has been related to the development of depression. Specifically, it is believed that individuals who attribute failures to internal factors (self-blame) and successes to external factors (to other people or to luck) are more susceptible to developing feelings of helplessness, often followed by despair and depression. Locus of control also is hypothesized to have implications in the management of chronic health-related problems.
In oversimplified categorizations, individuals are labeled to have an internal or external locus of control. External individuals, who believe they have little control over what happens to them, are said to be more reactive to threat, more emotionally labile, more hostile, and lower in self-esteem and self-control. Psychophysiological assessment studies have revealed heart-rate acceleration and longer electrodermal habituation for externals in response to the presentation of tones under passive conditions. When faced with no-control conditions in stress situations such as inescapable shock, internals show elevated physiological arousal, while findings for externals are mixed. Thus, the locus of control has varying effects on physiology, depending on the circumstances. Such effects may play a role in psychological disorders such as depression and anxiety. Heightened physiological reactivity may also inhibit recovery from acute illness or affect the course of chronic health problems such as hypertension.
In addition to the relevance of personality to physiological reactivity and psychopathology, research has demonstrated that certain personality types may be risk factors or serve protective functions with regard to physical health. Type A behavior pattern and hardiness are two examples. The Type A behavior pattern is characterized by competitiveness, time urgency, and hostility. It has been identified as a potential risk factor for the development of coronary heart disease. Psychophysiological studies have suggested that, under certain laboratory conditions, males who exhibit the Type A pattern are more cardiovascularly responsive. This reactivity is the proposed mechanism by which Type A behavior affects the heart. More recent research has suggested that not all components of the Type A pattern are significantly associated with heightened cardiovascular reactivity. Hostility seems to be the most critical factor in determining heightened reactivity. Males who respond to stress with hostility tend to show greater heart-rate and blood-pressure increases than individuals low in hostility. Some research suggests that hostility is also a risk factor for heart disease in women.
In contrast to hostility, hardiness is proposed to buffer the effects of stress on physiology. Hardy individuals respond to stressors as challenges and believe that they have control over the impact of stressors. They also feel commitment to their life, including work and family. Psychophysiological studies have supported the buffering effect of hardiness. Individuals who are more hardy tend to be less physiologically responsive to stressors and to recover from stressors more rapidly. Again, the construct of hardiness seems to be more relevant for males, partially because males have been studied more often.
These studies show that various personality types can be distinguished to varying degrees by psychophysiological measurement. The implications of such findings include possible physiological contributions to the development of various psychological problems, and personality contributions to the development or course of physical disease. Many of those who study psychophysiology hope that it will lead to new biofeedback-based treatments for various psychological issues.
Evolution of Research
Although the sophisticated techniques and instruments that have enabled psychologists to study physiological events were not developed until the twentieth century, the notion that physiology and psychology (body and mind) are linked dates back as far as ancient Greece. Hippocrates, for example, described four bodily humors or fluids thought to influence various psychological states such as melancholy and mania. Although the link between mind and body has received varying degrees of emphasis in scientific thinking across the centuries, it regained prominence in the mid-1900s with the development of the field of psychosomatic medicine along with the widespread influence of Sigmund Freud’s theories of personality.
Psychosomatic medicine embraced the notion that personality and physiology are intertwined. Psychosomatic theorists believed that certain diseases, such as diabetes, asthma, and hypertension, were associated with particular personality characteristics. They suggested that personality influenced the development of specific diseases. Although much of this theorizing has been disproved, these theorists did return the focus to investigating the interactive nature of a person’s psychological and physiological makeup.
Psychophysiologists acknowledge the influence of personality characteristics on physiology and vice versa, and they are working to characterize these relationships. They hope that future work will better measure particular personality constructs and will clarify the interaction of gender with personality and physiology. Psychophysiologists also must be concerned with the external validity of the data they obtain in the laboratory. It has not been satisfactorily demonstrated that physiological responses measured in a given individual in the laboratory are at all related to that individual’s response in the natural environment. Thus, to establish fully the usefulness of laboratory findings, psychophysiologists must also study individuals in their natural environments. Recent technological advances will enable ongoing physiological measurement, which should achieve this goal and further establish the relations among personality, physiology, and behavior.
Bibliography
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