Consciousness Redux: Probing the Unconscious Mind; November/December 2011; Scientific American Mind; by Christof Koch; 2 Page(s)

Sigmund Freud popularized the idea of the unconscious, a sector of the mind that harbors thoughts and memories actively removed from conscious deliberation. Because this aspect of mind is, by definition, not accessible to introspection, it has proved difficult to investigate. Today the domain of the unconscious—described more generally in the realm of cognitive neuroscience as any processing that does not give rise to conscious awareness—is routinely studied in hundreds of laboratories using objective psychophysical techniques amenable to statistical analysis. Let me tell you about two experiments that reveal some of the capabilities of the unconscious mind. Both depend on “masking,” as it is called in the jargon, or hiding things from view. Subjects look but don’t see.

Unconscious Arithmetic
The first experiment is a collaboration among Filip Van Opstal of Ghent University in Belgium, Floris P. de Lange of Radboud University Nijmegen in the Netherlands and Stanislas Dehaene of the Collège de France in Paris. Dehaene, director of the INSERM-CEA Cognitive Neuroimaging Unit, is best known for his investigations of the brain mechanisms underlying counting and numbers. Here he explored the extent to which a simple sum or an average can be computed outside the pale of consciousness. Adding 7, 3, 5 and 8 is widely assumed to be a quintessential serial process that requires consciousness. Van Opstal and his colleagues proved the opposite in an indirect but clever and powerful way.