Traits have long been considered potential determinants of behavior and emotions. The authors of Personality Traits cite examples of references to characters or personality types as early as the fourth century BC, when Aristotle described dispositions. In the first edition of this book, published more than a decade ago, trait theory was described from an eclectic perspective, with emphasis on dimensions of personality and causes and consequences of traits. The new third edition has added emphasis on situational factors and how they influence trait expression and interactionism. Most notably, recent research on the neural bases of psychological states is presented. However, traditional psychological theory is not lost in the excitement over biological research, as social foundations underlying traits are also examined. Interestingly, there is added emphasis on “stress-buffering traits” such as spirituality, consistent with attention given to active coping styles that are commonly cited in clinical neuropsychology as correlating with better outcomes and quality of life.
Traits have been assessed in various manners, verbal report being the most common method. This presents an interesting dilemma for neuropsychologists in particular, since self-report is notoriously unreliable in clinical practice, at least in a population where there may be neurologic dysfunction, and in fact there are some ways to objectively assess trait-related behaviors. A recent article by Connelly and Ones (Reference Connelly and Ones2010) highlights this issue and the need for observer or collateral report in increasing validity of ratings.
Development of trait theory has been complicated by disagreement on a couple of issues. One is whether there is a causal status of traits, or directionality of causation from trait to behavior. This itself poses an interesting question for neuropsychologists. Recent research on plasticity and reorganization after amputation (and reattachment) has shown behavior (movement/action) can affect brain structure, so directionality of causation is perhaps more fluid within our specialty (Di Pino, Guglielmelli, & Rossini, Reference Di Pino, Guglielmelli and Rossini2009).
The authors detail psychometric approaches to trait theory with a surprisingly brief review of questionnaire construction and factor analysis. One criticism that could be made of the book is the scant attention statistical issues get, and also discordantly, that the one section on factor analysis, so crucial to trait theory, is so brief and exceptionally dry. Except for the most enthusiastic statisticians, clinical examples would be very helpful in this section. To the authors’ credit, there is quite a bit presented on the statistical support for various models and factors.
This volume establishes the primacy of the “Big Five” models of personality, as compared to three-factor models espoused earlier by Eysenck, with its classic trio of personality factors: neuroticism, extraversion, and psychoticism. Five-factor models are generally in favor today, although there is no one agreed-upon model. The most replicated is perhaps the model by Costa and McCrae, which includes the factors Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness, and led to development of the NEO-Personality Inventory. In this text, there is particular attention paid to language as a basis for trait structure. There is a so-called lexical approach to personality research in which natural language-based descriptors are sought, within and across languages. For the neuropsychologist who has an interest in language development and structure, this highlights a fascinating avenue for further reading.
The authors directly respond to criticisms of the stability of traits and their explanation of variance in behavior. Situationists believe the influence of traits varies depending on the situation: this may be a false argument since all major personality theories recognize situational factors influence behavior. But there are other situationist criticisms of trait theory, which the authors address point-by-point. Interactionism is the study of the interaction between the person (personality/traits) and situation and is described as an integral part of modern trait theory.
There is a brief section on cross-cultural research on traits, and this too may be a weakness of the book. Because of the importance of this issue in making determinations about biological bases of traits, it deserves more thoughtful critique. However, the authors do cite the available research honestly and clearly. The section on potential gender differences in traits is rather succinct as well, given the attention it has received in neuropsychological literature, at least in comparison. There is a fascinating chapter on “Personality across the life span.” Research appears to demonstrate both stability of traits over time, and also some plasticity, at least within the individual, and especially for less stable persons. The authors also discuss temperament, described as the study of traits or personality in infants and toddlers.
While traits are generally stable over time, states are fluid. It is theorized that mood influences how traits affect behavior. Chapter 4 looks at two major models of mood, and mood scales. This section may be more challenging for the casual reader, as it involves quite a detailed and technical review of state–trait theory, with the conclusion that the association between the two remains open to debate. A thoughtful chapter on challenges to trait theory is included, which is actually more of a review of how other personality theories mesh with trait theory (or do not, as in the humanistic approach). Again, this section may be very interesting but a little more difficult for those of us who have not refreshed our knowledge of personality theory since graduate school—and a humbling reminder of the complexities of personality theory and psychological measurement.
Part II is devoted to “causes of personality traits,” including genetics, psychobiology, and social psychology. A helpful discussion of models of trait research touches on twin, adoption, and molecular genetic studies—with an interesting side note on an evolutionary perspective of traits. While the significant genetic contribution to certain personality traits is described, a highly readable and interesting section on genetic covariation catches the eye. This refers to the study of the relationship between genetic influence on psychiatric disorders and the genetic influence on personality traits (which is thought to influence whether one develops a given psychiatric condition). There are recently published studies on the topic, for instance one relating genetic variation in certain personality traits with borderline personality (see Distel et al., Reference Distel, Trull, Willemsen, Vink, Derom, Lynskey and Boomsma2009), and a study on genetic variability in the trait “self-directedness” (Suchankova et al., Reference Suchankova, Baghaei, Rosmond, Holm, Anckarsater and Ekman2010).
The importance of this book for neuropsychologists is how trait theory fits into modern scientific investigation into brain structure and function. Chapter 7 addresses the psychobiology of traits, or specifically neuropsychological and neurophysiological aspects of trait theory. Although the authors cite reasons why there is presumed to be a link between personality and brain function, one reason—that sometimes—dramatic personality change can occur after brain damage—stands out as ironic for a book on trait theory: behavior certainly can change or vary after brain insult but it is more debatable whether that reflects any underlying change in personality traits. The authors give an interesting example of thinking of personality–biology interaction as being software (personality) versus hardware (neuronal) versions of information processing.
Several models of neural systems are covered. While Eysenck's and Gray's models (with emphasis on arousal and reward systems) seem overly simplistic today, Zuckerman's 1991 psychobiological model is also given attention, and other reading reveals updated versions of such models that incorporate brain imaging (DeYoung et al., Reference DeYoung, Hirsh, Shane, Papademetris, Rajeevan and Gray2010). There are alternative modern models of the neural underpinnings of personality that also deserve attention. The reader should note that a full review of psychobiological and personality factors is not included in this book but there is a detailed section on physiological testing and brain imaging as they relate to personality research (for instance, using EEG to examine “arousal” in extroverts and introverts). Perhaps lacking is critical analysis of the clinical utility of such techniques, including fMRI, which is a common topic of conversation in neuropsychology circles. While this line of research holds great promise, there are obvious limitations to interpretation (Dobbs, Reference Dobbs2005).
The next section, on the social psychology of traits, is more useful for the neuropsychologist, and is the first of several chapters that readers will find applicable to clinical practice. This section is one of the most interesting, especially given the emphasis on the interaction among cognition, social behavior and personality traits that is familiar territory for clinical neuropsychologists. A chapter on “Stress” includes considerable research on coping theories, which have garnered more attention recently as they relate to adjustment for caregivers of persons with neurologic conditions. Also, most neuropsychologists have experience in at least some aspects of behavioral medicine and behavioral health, and there is a section on personality traits and health that has great clinical utility for neuropsychologists. One wishes the section on models of psychosomatic illness was longer—not because it is central to the study of personality traits, but because the authors provide just a sample of that body of literature, which really is quite fascinating and certainly relevant to any neuropsychology practice.
Chapter 11 discusses the frequent assumption that on one end of a personality trait spectrum lies an “abnormal” trait. This is a timely topic given the recent media interest in development of the proposed Diagnostic and Statistical Manual of Mental Disorders-V, in which major changes to existing personality disorder criteria are proposed. Media coverage has generated criticism of the proposed changes by those who claim the new criteria would normalize pathological traits and behaviors. This is actually a fine chapter elaborating on problems with existing personality disorder constructs and validity and frankly, is suggested reading for all psychologists who may well encounter questions about media-highlighted changes in the DSM, and need to be able to address them fluently. Also, for neuropsychologists who do forensic work, the issue of personality disorder diagnoses will no doubt be a topic on the witness stand, and this chapter would be helpful preparation.
A chapter on performance research covers the theory that personality traits influence cognition, which can then be assessed in lab studies. The field of cognitive psychology, with its influence on information processing, has influenced the study of relationships between task performance and specific personality traits. Although the earlier chapter on neuroimaging was hypocritical of research limitations, this chapter elegantly describes studies on attention, working memory, and other areas of performance as they relate to personality traits. Interestingly, there is no strong correlation between any personality trait and “intelligence,” but personality traits are thought to perhaps influence competence and other aspects of cognition and learning and achievement.
A final chapter deals with applied personality assessment. Really, this is section on assessment and factors to consider in choosing personality questionnaires, and their uses in educational and clinical and organizational psychology. This is very interesting reading and the entire chapter has clinical utility for neuropsychologists, even if personality assessment is not part of one's usual routine.
In summary, Personality Traits is recommended reading for anyone looking for an updated review of trait theory, research on cognitive processing and personality, and especially an alternative approach to personality disorders as they currently exist in DSM-IV.
