Are our decisions our own? Philosophers, scientists, and the general public has long pondered both sides of the freewill vs. determinism debate.
American researcher Benjamin Libet found that actions perceived as freely voluntary are preceded by an electrical charge in the brain called the “readiness potential” (RP) about 550 ms before the act. Writing in the Journal of Consciousness Studies in 1999, Libet said “Human subjects became aware of intention to act 350-400 ms after RP starts, but 200 ms before the motor act. The volitional process is therefore initiated unconsciously.”
Some interpreted Libet’s findings as concrete evidence favoring determinism.
However, researchers from the Charité – Universitätsmedizin Berlin—using computer-based brain experiments—have discovered that humans are capable of canceling actions even after the brain has elicited an RP signal.
“If there is no chance of intervening, the dominoes will gradually fall one-by-one until the last one is reached,” the researcher wrote in Proceedings of the National Academy of Sciences. “A different possibility is that participants can still terminate the process, akin to taking out a dimono at some later stage in the chain and thus preventing the process from completing.”
In the study, the researchers asked participants to engage in a duel-like game with a computer. Subjects were presented with a light on a computer screen. When the light was green, the subjects waited a short period of time before pressing a floor-mounted button with their right foot. Points were earned if the button was pressed while the computer‘s light was green. But points were lost if the button was pressed after the computer light shifted to red. The subjects‘ brainwaves were monitored using electroencephalography (EEG). Eventually, the computer used the EEG data to predict the subject’s movements in an attempt to defeat the subject. In the study‘s third stage, the subjects were told the computer was attempting to predict their movements, and to try to outmaneuver it.
Subjects that successfully evaded the computer‘s predictions, which were based on the subject’s brain processes, are evidence that control over actions can be retained much longer than previously thought, according to Charité – Universitätsmedizin Berlin.
“Our data suggests that subjects can still veto a movements even after the onset of the RP,” the researchers wrote. “Cancelation of movements was possible if stop signals occurred earlier than 200 ms before movement onset, thus consituting a point of no return.”
