6.2: What is Personality?

The American Psychological Association defines personality as “individual differences in characteristic patterns of thinking, feeling and behaving” (American Psychological Association, 2020). Overall, personality traits represent enduring and consistent individual differences across the lifespan (McCrae et al., 2000; Roberts et al., 2006).

Personality differences originate from fundamental dispositions in early childhood, called temperaments (Rothbart, 2007). These fundamental dispositions influence the way people respond to environmental stimuli emotionally, cognitively, and/or behaviorally.Personality development is a continuous process beginning at an early age (Denissen et al., 2011). While individual expressions of personality are generally considered culturally conditioned manifestations of several factors (Eysenck, 1970;Funder, 2001; McCrae et al., 2000), personality is moderately to highly heritable (Bouchard & Loehlin, 2001; de Moor et al., 2012), suggesting an evolutionary and biological basis (Gray, 1991; Zuckerman, 2005). Biological theories present varying postulates regarding the underlying neurobiology from which personality arises, though none have been universally supported. Common themes that have emerged, however, include individual differences in arousal (tonic neural activity), reactivity (stimulus/response threshold), and self-regulation (recovery from evoked responses; Depue & Collins, 1999; Gray & McNaughton, 2000; Zuckerman, 2005).

Personality theory dates back to the classical theory of the four humours (sanguine, phlegmatic, choleric, and melancholic), put forth by Hippocrates (460 BC) in his treatise “On the Nature of Man”. The ideas put forth were further endorsed by Galen during the second century AD in his famous treatise “On the Natural Faculties”, which preceded his work “On Temperaments” in which he describes an optimal temperament in which all four humours are in balance without any quality being in excess (Stelmack & Stalikas, 1991). The theory of the humours and the resultant fourfold typology of temperament/personality persisted through the middle ages into the Renaissance. With advances in medical science during Medieval times, the physiological models elaborated by Hippocrates were disproven and the psychological postulates were also presumed falsified; ultimately, the theory fell out of favor. Remnants of the fourfold typology were later observed in the writings of Immanuel Kant (1789) and Willhelm Wundt, the “father of psychology” (Stelmack & Stalikas, 1991). The theory put forth a number of ideas that remain important to our current thinking. Specifically, a) the fourfold typology resulted from consistently observed patterns in the person’s emotions and behavior; b) it was linked to human physiology as it was understood at the time; and c) it was related to psychopathology.

Early work in psychology reiterated the notion of personality “types” reflected in the personality types and somatotypes described by Carl Jung and William Sheldon, respectively (Jung, 1923; Sheldon & Stevens, 1942). However, an overwhelming body of factor analytic and psychobiological research has nullified the perspective of personality as “types”. Nevertheless, these theories made important contributions to considerations for personality moving forward. For example, though Sheldon’s theory of somatotypes (i.e. the idea that body types had a causal relationship with personality) has been logically and scientifically refuted (e.g., Hammond, 1957; Lerner, 1969; Slaughter, 1970), significant associations between body type and personality do exist (Sutin & Terracciano, 2016)and highlight relationships between psychological individual differences in health behaviors contributing to body composition and overall health (Ferguson, 2013). Though the work of Carl Jung has received its fair share of criticism, his was the first theory to highlight Extraversion/Introversion as a primary personality factor and his ideas about four functions or modes of operation for personality (i.e. thinking, sensing, intuition,and feeling) persist in popular culture as reflected in the widely used Myers-Briggs type indicator (Barbuto, 1997). Despite the theoretical and scientific advances since these early perspectives, their imprint on contemporary thought is undeniable. Much progress has been made since this early work to understand the structure of human personality and it should go without saying that our current perspectives differ markedly from those in the early 20^th century.

Our current view of personality follows a common higher-order trait taxonomy, in which primary traits act as determinants of lower-order sub-traits which are used to describe individuals with greater specificity and detail, but which are also subject to greater influence by external factors (see Figure 6.1). Thus, primary personality traits represent the peak of a conceptual hierarchy, with the most stable, biologically based traits at the top and individual level behaviors at the bottom, with narrow facet traits linking biological individual differences to situation specific individual level behavior. Factor analytic work by scholars throughout the 20^th century (e.g., Cattell, 1947; Digman, 1990; Eysenck, 1947; Goldberg, 1993; Thurstone, 1934; Tupes & Christal, 1961; Webb, 1915)provided a top-down template for classifying personality as intercorrelations between descriptive terms. This body of work leveraged the lexical hypothesis (ca. 1884), which states that those personality characteristics that are most important in peoples’ lives will eventually become part of their language; thus, terms for personality traits are identifiable across cultures through analysis of their descriptive words for individuals (i.e., trait terms; Allport, 1927; Allport & Odbert, 1936). This work, conducted in tandem with the pioneering work by Hans Eysenck elaborating biological models of Extraversion and Neuroticism (Eysenck, 1970), has helped bridge the gap between specific sub-traits and more general personality factors that resulted in a previously disparate field of study (Digman, 1990; Goldberg, 1993).

Figure 6.1: Visual Representation of the Hierarchical Nature of Personality Depicted Across Levels of the Primary Trait Conscientiousness.

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Currently, the dominant contemporary taxonomy used by scholars worldwide is the Five Factor Model (FFM) of personality (McCrae & Costa, 2008; Revelle et al., 2011), or similar variants of this model. This widely supported system postulates that the core personality of all people can be classified on five bipolar dimensions: (1) Extraversion/ Introversion; (2) Neuroticism/ Emotional Stability; (3) Conscientiousness/ Undirectedness; (4) Openness/ Closedness; and (5) Agreeableness/ Antagonism. Though it is recognized that these terms each reflect one extreme end of the respective bipolar dimension, the trait terms listed here in italics are those typically used to discuss each dimension within the literature. Their counterparts are seldom called out by name, rather, scholars often refer to individuals as scoring either high or low for Extraversion, for example. Nevertheless, it is important to recognize the continuous nature of these dimensions, and to keep in mind that all people can be classified according to their respective scores on each of the Big Five personality dimensions. Descriptions of dispositions or tendencies displayed for high and low ends of each dimension are listed in Table 6.1. Notably, though there are some sub-traits (e.g., sub-traits of Neuroticism) and trait clusters, such as the dark triad (i.e., narcissism, Machiavellianism, and psychopathy), that do represent trait indicators of psychopathology, all Big Five are generally considered to have some evolutionary utility, and to be normal variations of fundamental, biologically based personality traits across the general population.

Table 6.1. Characteristic Tendencies of Individuals Scoring on the High or Low End of Each Bipolar Dimension of the Big Five personality Factors

This widely supported taxonomy emerged organically through decades of factor analytic work (Digman, 1990). Further, the Big Five are observed to be moderately heritable (Jang et al., 1996; Riemann et al.,1997), are related to childhood temperament (Ahadi & Rothbart, 1994; Rothbart et al., 2000), follow a stable and predictable trajectory of change over the lifespan (Roberts et al., 2006), and are significantly related to several indices of physical health and psychological well-being (Ferguson, 2013; Steel, Schmidt, & Shultz, 2008). The Big Five are considered to be the core dimensions of personality, and to interact with one’s environmental exposures resulting in the expression of more specific sub-traits, (Goldberg et al., 2006; McCrae & Costa, 1995). For example, individuals high in Extraversion may express this higher order trait through excitement seeking, sociability, a positive outlook, or energetic activity under circumstances that facilitate such an expression, whereas these traits would not manifest under the same circumstance for an individual low in Extraversion (i.e. high in introversion). Most theorists agree that primary traits interact with external factors to produce narrower, more contextualized social cognitive and motivational characteristics which strongly influence behavioral action (Ajzen, 1991; Bogg et al., 2008; McCrae & Costa, 1999; Mischel & Shoda, 1999; Rhodes, 2006). A detailed elaboration of this integrative perspective of the personality system is detailed in the Five Factor Theory (McCrae & Costa, 1999, 2008), and a contextualization of these concepts to physical activity and exercise behaviors was recently published for consideration by health professionals interested in using personality to maximize physical activity and exercise outcomes (Wilson, 2019). Generally, integrative theories of the personality system indicate that the way one responds to any external or internal stimulus is moderated by their underlying core personality (which is reflective of individual differences in neurobiological arousal and reactivity in relevant neural networks). Personality is therefore expected to moderate the environmental influences on cognitions, affect,and behavior, making it a salient source of systematic variation in outcomes of interest to a wide-range of behavioral interventionists (Ferguson, 2013).

6.2.1. Personality Measurement

Personality assessment can be approached via self-or proxy-report survey, behavioral observation, or the measurement of psychophysiological correlates (de Geus & Neumann, 2008; Lanyon & Goodstein, 1997). Most frequently, personality is assessed using a validated self-report measure. Survey assessments ask people to rate how well an adjective or sentence describes themselves or someone they know. Common proxy respondents include teachers, parents, or close friends of the individual being assessed.Validated survey instruments often allow users to compute summary scores for traits measured, though reports of normative scores for personality are uncommon, making interpretations of sample representativeness difficult. Surveys are generally easy to implement, low cost, and low burden for the researcher and participant, though they do have some notable limitations. Primarily, survey assessments are vulnerable to response bias (e.g., socially desirable responding or experimental demand). To minimize this possibility, some surveys use “distractor” items that do not ask about personality characteristics, attempting to conceal the purpose of the survey from the participant. Another common approach is to mix the personality assessment items in with items from other surveys in a single question block. Both approaches aim to reduce the potential of response bias resulting from participants deducing what the survey is attempting to assess and tailoring their answers in some way. Some commonly used, well-supported surveys for assessing the Big Five traits include the Big Five Inventory (John et al., 1991), and the NEO-PI-R (Costa Jr & McCrae, 2008). Another resource that many find especially useful is the International Personality Item Pool (IPIP). The IPIP is a free resource in the public domain including more than 3,000 items from over 250 personality scales which are available to be copied, edited, translated or otherwise used for any purpose without seeking permission or paying a fee for use (Goldberg, 1999; Goldberg et al., 2006). Interested readers are encouraged to go to https://ipip.ori.org/ to explore the resource and its applicability for their assessment needs.

Unlike survey assessments, behavioral observations and psychophysiological measures are uninfluenced by participant response bias. Behavioral observations involve coding and analysis of observations made in-person or via video recording. This approach is time-consuming and carries a substantial researcher burden. Coding observations requires careful consideration and control for external conditions, as low inter-rater reliability commonly results from the influence of environmental and situational variables (Rowe & Kamphaus, 2008). To date, observational assessments of personality are rarely used in the exercise and physical activity literature.

Finally,psychophysiological correlates of personality can be used as a proxy measure for biologically based traits. Significant relationships are consistently reported between psychophysiological reactivity and self-reported measures of personality (de Geus & Neumann, 2008). Individual differences in sensory stimulus response of localized brain activity are related to personality as observed in studies using functional magnetic resonance imaging and electroencephalography. Personality modulates responses such as evoked asymmetry and event-related potentials (e.g., error-related negativity, contingent negative variation; Canli et al., 2001; Coan et al., 2006; Pailing & Segalowitz, 2004). For example, individual differences in cerebral blood flow have been observed between introverts and extraverts using positron emission tomography such that introverts are reported to have greater cerebral blood flow in the frontal cortex at rest than extraverts (Johnson et al., 1999). Additionally, indicators of autonomic nervous system responses (e.g., electrodermal conductivity, heart rate variability, pre-pulse inhibition and magnitude modification of the startle reflex) to stressors and emotional stimuli may be useful indicators of personality differences, though evidence to date has been mixed (de Geus & Neumann, 2008). Like behavioral observation, the assessment of psychophysiological correlates of personality in the exercise and physical activity literature has been underutilized.