IF YOU ever felt paranoid about subliminal messages, you might be right to worry. Images we see but don’t consciously register have been shown to inform people’s decision-making.

Joel Voss of Northwestern University in Evanston, Illinois, and colleagues showed volunteers 12 kaleidoscope images for 2 seconds each while they also performed an unrelated number task to distract them from consciously committing the images to memory.

A minute later, volunteers were asked to look at pairs of similar-looking images and choose the one they had seen before. They were also asked whether they were sure, had “a feeling” they were right, …