dean radin is conducting true experiments.ctually react to things before they happen. >> and when you're ready to begin the trial, you press the button. >> reporter: have you always believed in premonitions? >> i would say no. as a scientist, i tend to base belief on evidence. >> reporter: here's how it works. radin monitors a subject's heart, brain and skin, measuring how they react to random visual images like this. so you don't know which picture's coming up next. and -- >> i don't know. >> reporter: -- the test subject certainly doesn't have any idea. >> right. >> reporter: most people react the way you would expect. they become upset after they see images indicating violence. they get aroused by sexual imagery and stay calm when shown a tranquil scene. >> you got excited because -- >> reporter: but remarkably, radin claims one in five have those reactions up to nine seconds before they see the pictures, a phenomenon known as presentiment. how can that be? how do you know this isn't just coincidence? >> there are over 40 s