Two parallel (and sometimes conflicting) brain systems for evaluating others.

The Editor's Choice section of the Jan. 5 Science magazine has a brief review of interesting work by Rydell et al. at Miami University:

"One emerging theoretical view posits two systems of reasoning: a slow-learning system that acquires and classifies associations over long periods of time, and a fast-learning module that emphasizes higher-order conscious cognition. A stimulus--for example, the negatively valenced word "hate"--can be paired in a subliminal fashion with a person's face (for example, Bob's); this association will induce subjects to regard Bob unfavorably, as assessed by their poststimulus choice of positive or negative adjectives, yet they will be unaware of having evolved this implicit attitude. Similarly, written descriptions of Bob's praiseworthy behavior will result in subjects expressing a liking for Bob, where this evaluation reflects a studied and thoughtful appraisal--that is, the formation of an explicit attitude. Rydell et al. show that these mental processes can be accessed separately and appear to operate independently. Not only are subjects capable of developing apparently inconsistent negative implicit attitudes and positive explicit attitudes about the same individual, but they can actually be influenced to invert their preferences by the subsequent presentation of subliminal (positive) words and supraliminal (negative) descriptions."