A smile or frown that lasts only a fraction of a second can mean a lot to your business. That's because such responses reflect a consumer's opinion more accurately than anything said in a focus group, says market researcher Dan Hill, author of Body of Truth, a new book on the marketing applications of facial coding research. "We feel before we think," Hill explains, "and 95% of thought is subconscious."

Hill "shows companies what their customers can't or won't say."

The science behind facial coding was first theorized by Darwin and was developed in the 1970s by San Francisco psychologists who found that all people display "micro-expressions" that mean the same thing regardless of culture. Hill's company, Sensory Logic in St. Paul, Minn., tracks these common winks and smirks using video cameras and facial sensors, to test if target customers respond favorably to products, ads, and packaging.

Facial coding has its critics. The system is used by police and the FBI to question suspects, prompting critics to charge that classifying people by physical data can lead to racial profiling. But in terms of market research, Hill defends facial coding as a way to help companies avoid mistakes. For example, he once tested signs for U-Haul that touted cheap moving vans. Facial coding picked up frowns. "Customers began worrying about terms and conditions, the contract, and other hassles," Hill says. An image of a van on the open road brought grins, he adds, because "U-Haul emerged more as a friend."