What if we’re not the magnanimous people we think we are? That seems to be the conclusion of the past few decades of social psychology research. Freud stuck a dagger in the comforting idea of complete, conscious self-awareness, but experimental findings suggest that not only do we not know ourselves, if we did, we might not invite ourselves over for dinner.

This research takes Freud’s dagger into our vanity and twists it. One of the greatest sources of torque is what’s called the Implicit Association Test, a computer-based assessment that susses out unconscious biases. One version, the Race IAT, reveals that 75 percent of its takers, including some African Americans, have an implicit preference for white people over black people. The story of the IAT, and of prejudice in general, is told in the accessible and authoritative “Blind Spot” by Mahzarin R. Banaji, one of the test’s chief developers, and Anthony G. Greenwald, the researcher who created it in 1994.

Before reading on, I suggest that you join millions of others and take a test yourself. Go to implicit.harvard.edu and click on “Demonstration.” You’ll have a choice of a dozen or so tests (included are Weight, Age and Race IATs), but not before reading a disclaimer: “If you are unprepared to encounter interpretations that you might find objectionable, please do not proceed further.” The glint of the knife.

The Race IAT works like this: One at a time, it presents black faces, white faces, good words (“joy,” “love,” “peace,” etc.) and bad words (“evil,” “failure,” “hurt,” etc.), and you must respond as quickly as possible by pressing one of two keys. If you work faster when good words are assigned to the same key as white faces, you purportedly prefer white people.

Some psychologists have critiqued the paradigm by saying it merely tests awareness of stereotypes, not endorsement of them. But the subconscious cannot distinguish between the two; it speaks only in the language of association. It can handle “white equals good,” while a distinction such as “other people believe white equals good” gets lost in the wash.

‘Blindspot: Hidden Biases of Good People’ by Mahzarin R. Banaji and Anthony G. Greenwald (Delacorte)

The best indicator of the test’s validity is its prediction of behavior. An automatic white preference has been found to correlate with, for instance, suboptimal treatment of black emergency room patients, unfavorable judgment of black job applicants, laughter at racist jokes and voting for John McCain over Barack Obama. What’s more, scores on the Race IAT predict such discrimination even better than do overt statements about one’s beliefs. Banaji and Greenwald suspect that the discrepancy between implicit tests and explicit statements results in part from reputation management — people don’t want to express their biases openly — but mostly from dissonance reduction: They don’t want to admit their biases to themselves.

Self-deception is understandable. Greenwald describes becoming aware of his automatic white preference as a “moment of jarring self-insight. . . . I can’t say if I was more personally distressed or scientifically elated to discover something inside my head that I had no previous knowledge of.”

Most of us may hold racial biases — the starring bias of the book — but Banaji and Greenwald don’t go so far as to say America is racist, at least not as usually understood. Here is one place where the authors put forth something that feels somewhat novel (Malcolm Gladwell has discussed the IAT on “The Oprah Winfrey Show,” after all): Banaji and Greenwald propose that most of today’s racial discrimination stems not from attempts to harm anyone but from selective helping. We’re each part of several groups, defined by race, gender, religion, family, alma mater and so on, and when we go out of our way to help an in-group member, we don’t see that as a bad thing. We’re being “good” people. But such selective privileging reinforces the status quo. The rich get richer, and the rest fall behind.

Of course, selective helping doesn’t explain all discrimination, such as the sidelining of the old or overweight. And we can also handicap ourselves through self-stereotyping. For instance, women who associate female with family and male with career — that’s 80 percent of female respondents — may not feel at home in graduate school or the corporate world and may abandon professional aspirations.

The book’s tone is careful and professorial, though not academic — there’s the occasional joke and exclamation point. Banaji and Greenwald, professors of psychology at Harvard and the University of Washington, respectively, make a point of sticking close to the data. But while they cover a lot of ground in a short book, with their combined expertise I would have enjoyed a bit more venturing into poorly charted territory. One question: If my implicit and explicit attitudes disagree, which is my real attitude? Which reflects the real me? Is it more defining that I failed the Race IAT or that I voted for Obama? This question may have no good answer and may be ill-formed to begin with — is there a single “real” self? — but it’s one worth addressing. Here’s a stab at an answer: If an attitude affects your behavior, it is part of you. Implicit and explicit attitudes affect behavior in different circumstances, so they are both “you.”

In a partially uplifting note, Banaji and Greenwald argue that while we may not have much power to eradicate our prejudices, we are often capable of counteracting them. The first step is to turn a hidden bias into a visible one.

bookworld@washpost.com

Matthew Hutson , a science writer living in New York City, is the author of “The 7 Laws of Magical Thinking: How Irrationality Keeps Us Happy, Healthy, and Sane.”

BLIND SPOT

Hidden Biases of Good People

By Mahzarin R. Banaji

and Anthony G. Greenwald

Delacorte. 254 pp. $27