Consumer-products companies are turning to new technology to overcome the biggest obstacle to learning what shoppers really think: what the shoppers say.

It turns out consumers aren't a very reliable source of information about their own preferences. Academic research has shown focus-group subjects try to please their testers and overestimate their interest in products, making it hard to get a read on what works. But getting testing right is crucial for consumer-products companies because they ship high volumes and lack direct...