Let’s Think Things Over

Freud’s division of mental life into the conscious, preconscious, and unconscious was based on a rudimentary model of the nervous system. A century later, German investigators using functional MRI (fMRI) have bolstered his notion that the unconscious continuously influences conscious thought.

Previously, the investigators had found a lag of a few hundred milliseconds between electrical activity in the supplementary motor area, which prepares for motor action, and an individual’s indication of the decision to press a button. In the current experiment, 14 volunteers watched a series of letters flash on a computer screen and pressed a button with either their left or right hand whenever they wished; immediately afterward, a screen appeared on w…