According to Plutarch, the inscription at the Delphic Oracle advised, "Know thyself." To which Timothy D. Wilson, professor of psychology at the University of Virginia, Charlottesville, responds, "Good luck."

Dr. Wilson is one of a growing number of psychologists and neuroscientists whose research is showing the importance of the unconscious -- "mental processes that are inaccessible to consciousness but that influence judgments, feelings or behavior," as he puts it. But this isn't Freud's unconscious, that maelstrom of primitive emotions and repressed memories.

Instead, the unconscious being excavated by scientists processes data, sets goals, judges people, detects danger, formulates stereotypes and infers causes, all outside our conscious awareness.

In fact, there is a growing consensus that the unconscious is a pretty smart cookie, with cognitive capacities that rival and sometimes surpass that of conscious thought. How smart is the unconscious? Two experiments probing the power of intuition sold me.

In one, volunteers watched a computer screen divided into quadrants. Whenever an X popped up, the volunteer was to push a button indicating which quadrant it occupied. Unbeknownst to the volunteers, the appearance of the Xs followed strict and somewhat arcane rules (the X never appeared in the same square twice in a row, for example, and never reappeared in its first location until it had shown up in two others).

The volunteers got faster and faster at pressing the right buttons. That suggests they anticipated the X's appearance correctly, or at least knew where it wasn't going to be. But none could verbalize this -- or even tell the scientists that there were hidden rules. They just seemed to know intuitively what was going on.

In another study, researchers led by the noted neurologist Antonio Damasio of the University of Iowa, Iowa City, had volunteers draw from four decks of cards. Each card was marked with an amount "won" or "lost." Two decks had big wins and losses and, if played consistently, yielded a net loss; the other two had smaller wins and losses and, over time, returned a net gain.

Almost all the volunteers learned to avoid the risky, losing decks, though as in the game of X's, none could articulate why the losing decks gave them a bad feeling. But if the conscious part of their brain was confused their body was not: choosing from the losing decks increased skin conductance, which measures minute levels of sweat and correlates with stress.

Volunteers with damage to the brain areas called the ventromedial prefrontal regions, however, never experienced a rise in skin conductance and never learned to avoid the bad decks. Our "gut feelings" reside behind our forehead, not in our digestive system.

An association between two events -- such as the appearance of a new X and the location of the previous ones, or a deck of cards and gambling losses -- is called a covariation. Covariation is extraordinarily tough to spot (whole forests have been felled for textbooks explaining how to prove covariation statistically). Yet somehow the adaptive unconscious does it intuitively, and better than conscious mental processes.

This sophisticated system operates under the radar of consciousness not because it has something to hide, as Freud argued, but for the sake of efficiency. We need to process so much information to survive that some of it has to occur unconsciously, much as a computer runs on machine language that no one wants to see on the monitor. Even while our mind is otherwise engaged, we can profit from unconscious calculations.

The adaptive unconscious also sizes up people's motives, character and intent -- judgments crucial to reach quickly. It even seems to have its own personality. Although conscious personality influences deliberative responses, the adaptive unconscious guides responses made unthinkingly.

Do you regularly snap at underlings who mess up in meetings? Blame your unconscious personality. After rumination, do you invite them into your office for a helpful chat? That reflects your conscious personality. Do you hold doors for old ladies but swear at drivers who cut you off? Your conscious personality is kind, but your unconscious might have an angrier, aggressive bent.

Contrary to revealing our deepest feelings, motives and beliefs, looking inward can be counterproductive -- as I'll describe next week. For now, as you head off for the unofficial last weekend of summer, don't agonize over whether to hit the beach or the mountains: Follow your gut. Er, your unconscious.

Write me at sciencejournal@wsj.com¹.

Updated August 30, 2002