News you can use for Valentine's Day: When you gaze into your sweetheart's eyes, look for enlarged pupils. Psychologist Bruno Laeng, of the University of Oslo, says our pupils don't just respond to light, but to thoughts too. Studies show that our pupils dilate when something captures our attention, including when we feel strong emotions. Laeng discusses how psychologists are using "pupillometry" in the lab.
archival footage: prelinger archive