What choices we make may depend a lot on the state of the brain and random fluctuations in the brain's background electrical noise just prior to making a decision.
Decisions could be predicted based on the pattern of brain activity immediately before a decision was made, the findings showed.
"This shows how arbitrary states in the brain can influence apparently voluntary decisions," said Jesse Bengson, a post-doctoral researcher at University of California, Davis.
For the study, researchers sat volunteers in front of a screen and told them to fix their attention at the centre while using electroencephalography (EEG) to record their brains' electrical activity.
The volunteers were instructed to make a decision to look either to the left or to the right when a cue symbol appeared on screen, and then to report their decision.
The cue to look left or right appeared at random intervals, so the volunteers could not consciously or unconsciously prepare for it.
"The brain has a normal level of background noise as electrical activity patterns fluctuate across the brain," Bengson said.
The researchers found that the pattern of activity in the second or so before the cue symbol appeared - before the volunteers could know they were going to make a decision - could predict the likely outcome of the decision.
"The state of the brain right before presentation of the cue determines whether you will attend to the left or to the right," Bengson added.
The study appeared in the Journal of Cognitive Neuroscience.
