Press Release

 Brain imagery confirms that the brain can function unconsciously

Paris, October 8, 1998
 
Is it possible to understand a written word without even being conscious of having seen it? The hypothesis of subliminal perception has just received additional confirmation with the publication in Nature of an article describing a study conducted by researchers of the Frederic Joliot hospital service at the CEA in Orsay, INSERM (U-334) and the CNRS (Cognitive and psycholinguistic sciences laboratory). Using the methods of cognitive psychology and state-of-the-art brain imagery techniques, they were able to demonstrate that a word shown for a very brief moment to a person is unconsciously identified by the latter's brain. Furthermore, this unconscious activity is not restricted to the parts of the brain specialized in sensorial perception, but involves the same regions which are at work during conscious processes.

Previous studies in the field of psychology have demonstrated that the brain is capable of unconsciously perceiving pictures or words which subjects are not aware of having seen, due to the speed at which they were shown. However, so far, little is known about how the brain processes this subliminal information and the actual parts of the brain involved in this process. The study conducted by researchers of the Frédéric Joliot Hospital at the CEA (Orsay), of INSERM Unit 334 and CNRS URA 1198, under the supervision of Stanislas Dehaene, complements the findings of psychology thanks to brain imagery and brain activity measurement techniques.
Their study was carried out in the following manner:
Several pieces of information were shown on computer screens to different subjects in the following order:
A random series of letters (for instance QDJGLS)
A number (for instance SEVEN)
Another random series of letters (for example HJKQKF)
A second number (for instance NINE)
The first number is shown very briefly, during 43/100 of a second, so that it is literally invisible: even people who know that it is being shown cannot see it or read it. The second number, on the other hand, is shown long enough to be read. The perception of the first number, even though unconscious, influences the behaviour of the subject. Indeed, when the researcher asks the subject if the second number (in this case, nine), is larger or smaller than five, the latter's answer comes faster if he has been subliminally shown an intermediary number (in this case, seven). The subject took into account the number seven, even though he was unaware of it; this implies that the hidden figure was identified by the subject who unconsciously assessed its numerical value.
While the subjects gave their answers by pressing a button, the researchers recorded the electrical activity of their brain (electroencephalogram: EEG) or used nuclear magnetic resonance imaging techniques. This method complements EEGs; it is sensitive to blood flow variations in the brain due to a single brain activity: it can locate very precisely the part of the brain where the unconscious activity is taking place, whereas the EEG describes the process in time. Results show that the hidden information influences the entire information processing activity of the brain, and not only the zones concerned by sensorial perception. On the contrary, even the cortex, which commands movement, a function which is quite separate from intellectual command, is activated. Thus, the areas of the brain involved in the processing of unconscious information are quite comparable to those involved in the processsing of conscious information. Of course, in more complex tasks, conscious processing may involve specific parts of the brain.
These recent results confirm that to a large extent, our brain functions unconsciously. Visual identification, understanding the meaning of words, and even the programming of movement can happen without our being aware of it. This study is extremely significant in that it enhances our understanding of the cerebral nature of conscience, an issue which has caused much debate in this "decade of the brain ".

Reference:
S. Dehaene, L. Naccache, G. Le Clec'H, E. Koechlin, M.Mueller, G. Dehaene-Lambertz, P.F. van de Moortele, D. Le Bihan. Imaging unconscious semantic priming. Nature, October 8, 1998.

Contact: Stanislas Dehaene
Service hospitalier Frédéric Joliot du CEA - Orsay

 

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