According to research published in the Journal of Cognitive Neuroscience, human choice is born out of predictable electric impulse in the brain which suggests that human beings do not possess free will but are slaves of determinism. Read the full article here in the Independent Online. JoCN is published by the Helen Wills Neuroscience Institute out of Berkley.
Volunteers within the experiment conducted at the University of California, Davis were asked to sit in front of a screen and focus on its central point while their brains' electrical activity was recorded. They were then asked to make a decision to look either left or right when a visual cue appeared on the screen, and then to report their decision.
Based on the brain activity, researchers could determine with reasonable accuracy which way the volunteers would look.
(I shudder to think how much money was spent to discover something that Penn Jillette could have offered for free or at least for the cost of a ticket to his next show, but such is the politics of science.)