Susan Cain: Quiet: The Power of Introverts in a World that Can't Stop Talking. New York: Crown, 2012.

Cain's book is a valuable compilation of what is known today about introverts and introversion -- from the research of psychologists, to labs, boardrooms, classrooms, academic offices, conferences, personal observation and interviews by the author, and a deluge of books, articles, and Internet sources. Cain deftly assembles the data into a unifying theme celebrating the strengths of introversion. Underlying the data are her own experiences as an introvert, from childhood to corporate lawyer to skills trainer to writer. The book is an excellent blend of the personal and anecdotal with the factual and informational. This review concentrates on the informational, but the charm and persuasion of the anecdotal rounds out the pleasure of reading and making the data relevant to daily life.

Introversion (and extroversion) were terms coined by Carl Jung to describe personality types with respect to responsiveness or sensitivity to environment, events, and energies. As Cain succinctly puts it:

Introverts are drawn to the inner world of thought and feeling, said Jung, extroverts to the external life of people and activities. Introverts focus on the meaning they make of the events swirling around them, extroverts plunge into the events themselves. Introverts recharge their batteries by being alone; extroverts need to recharge when they don't socialize enough.

Contemporary psychology accepts and extends the two categories to, for example, the workplace, noting that extroverts work quickly, multitask, and take risks, motivated by thrill and reward. Introverts work slowly, deliberately, are concentrated and detail-oriented, immune to wealth and fame as motivators. In social settings, extroverts prefer activity, participation, spontaneity, even conflict, being assertive, dominant, and thriving in company. Introverts may participate in social settings but are measured, thoughtful, given to listening rather than talking, discrete, compliant, prefer the serious to the frivolous, prefer writing to talking.

But, as Cain says pointedly:

The word introvert is not a synonym for hermit or misanthrope. Introverts can be these things, but most are perfectly friendly. ... Nor are introverts necessarily shy. Shyness is the fear of social disapproval or humiliation, while introversion is a preference for environments that are not overstimulating.

(The wisdom of this insight alone, presented early in the book, will compel introverts  to want to read on, with great interest.)

Degrees of sensitivity to environment and stimuli basically distinguish degrees on the spectrum of personality, with introverts more acutely sensitive to people, sounds, and environment. Extroverts require more stimuli in order to respond productively to their environment.

Yet the Extrovert Ideal (to use Cain's capitalization) dominates American culture. This is partly explained by the 19th-to-20th century shift in economics and cultural values from agrarian and rural to urban and technological -- from the culture of character emphasizing personal integrity, to the rise of capital, wealth and commerce celebrating the culture of personality, exemplified in the triumph of the salesman over the farmer.

Cain follows these important historical points with illustrative reports of first-hand experiences with the culture of personality and the dominance of the business and corporate models of personality in society in general. Here the focus is on what the author calls "New GroupThink, "when collaboration kills creativity." Teamwork and brainstorming are unproductive pitfalls of groupthink. They fail because of three factors identified by industrial psychologists: social loafing, production blocking, and evaluation apprehension. Yet teams dominate more and more schoolwork as well as workplaces with the false promise of teaching cooperation and tolerance. The loss, rather, is in both creativity and individual responsibility.

Pursuing a physical source for temperament, the author interviews the well-known developmental psychologist Jerome Kagan, whose pioneering research identified nervous system reactivity with personality. Children may inherit up to 50% of genes dominant for personality. High-reactive infants seem to overreact to stimuli, a predictor not of extroversion but of a later caution and malleability that presages stability in adversity, fearfulness (which translates to caution in risk-taking) -- in short, a resilient "rubber-band" personality.

Brain stem amygdala and cerebral or frontal cortex (the contrast of reactive and intellectual centers) are the physical factors specifically of interest in new psychological views of personality. While this information is not new, the introvert/extrovert application is a tantalizing line of inquiry.

Over-arousal and under-performance  are the introvert's weaknesses in work settings, while under-arousal and over-performance characterize extroverts. These observations have important implications for workplace managers but also for individuals and the people around them: their family and loved ones. Notes Cain:

Once you understand introversion and extroversion as preferences for certain levels of stimulation, you can begin consciously trying to situate yourself in environments favorable to your own personality -- neither over-stimulating nor understimulating, neither boring nor anxiety-making. You can optimize your life in terms of what personality psychologists call "optimal levels of arousal" and what I call "sweet spots," and by doing so feel more energetic and alive than before.

Reactivity is a fascinating theme to pursue in understanding personality. Scientists have identified fast versus slow in over a hundred animal species, usually falling into the 80/20 ratio reflective of human beings. The evolutionary trade-off exists because both personalities exhibit successful survival skills. Slow animals are observant, forge less, and avoid predators; fast animals sally forth into danger; hence the necessary higher ratio. Likewise with humans. Cain quotes Jung on the trade-off:

[Extroversion] consists in a high rate of fertility, with low powers of defense and short duration of life for the single individual; the other [introversion] consists in equipping the individual with numerous means of self-preservation plus a slow fertility rate.

Biologists also identify -- besides fast/slow and sly/bold -- hawk/dove, traits that involve aggression versus nurturing. Here is another fascinating train of thought re personality.

The author elaborates on the role of dopamine in extroverts' risk-taking behavior. Sheer recklessness in the financial management of recent years is an excellent example of the phenomenon of excess risk, excess extroversion. Business school professors and psychologists note traders' disdain for useful fear and doubt, but especially the extroverts' reaction to trouble by actually accelerating the risky behavior, of being "geared to respond," a strong (and well-documented) characteristic of buzz-prone reward-oriented extroverts. This behavior contrasts not with a slow dim-wittedness but with a thorough and circumspect introversion where work fits a flow, as psychologist Mihaly Csikszentmihaly argues. Flow is where neither avoidance nor reward is the motivator. Cain's "sweet spots" fits the flow process. What remains is for the individual to be conscious of the patterns.

Finally, too, Cain offers a detailed chapter on how introverts and extroverts can and do get along, within families, in relationships, socially, and especially in workplaces. The book concludes with a practical blueprint of advice for introverts -- and the extroverts who live and work with them. Introverts need a persona, carefully crafted for rough situations, but, Cain advises them not to hide behind it.

Wherever you are, bear in mind that appearance is not reality. Some people act like extroverts, but the effort costs them in energy, authenticity, and even physical health. Others seem aloof or self-contained, but these inner landscapes are rich and full of drama. So the next time you see a  person with a composed face and a soft voice, remember that she might be solving an equation, composing a sonnet, designing a hat. She might, that is, be displaying the powers of quiet.