Pushing the Boundaries of Conscious Access

By Yi Zhang, Ph.D.
November 3, 2011
There is so much that we can see in this world, yet did you know what we can’t see can in fact be perceived by the brain? It sounds pretty scary when our behavior is influenced by factors that we can’t see or explain, but it is so true. This actually happened at the 23rd Annual Convention of Association of Psychological Science where a group of psychologists sitting in the same room were presented an invisible target prime by a French psychologist named Stanislas Dehaene. Dr. Dehaene has dedicated most of his research career to the study of consciousness using priming methods.
In essence, a priming stimulus can be made invisible by very rapid presentation duration (usually less than 30 milliseconds) followed by a backward mask. During this kind of subliminal presentation, participants reported not seeing any prime, when asked to make a guess, they often guess correctly at a level much higher than chance.  In a way, what we can’t see somehow made it into our brain. In psychology jargon, subliminal means that the stimulus is inadequate to produce conscious awareness but able to evoke a response.
This has been taken by Dr. Dehaene as the boundary of conscious access, because if we can’t say what it is that we saw or if we saw anything, then we don’t have conscious access to that piece of information. But the information is right there at the subconscious level in the sense that it both produces behavioral results (above chance level report) and neural activation in the brain.
To understand what’s going on when people perceive something that they are not aware of, Dr. Dehaene systematically compared the primes that participants reported seeing versus not seeing using scalp recorded EEG (electroencephalogram).  A key difference in brain activation pattern emerged.  For subliminal primes to which there is no conscious access, brain activation was limited to the occipital visual cortex for the entire duration of perception (see diagram A).  For consciously perceived primes, brain activation during the first 100 milliseconds looked the same as activation by subliminal primes. Only one hundred milliseconds later, the whole brain burst into a sudden and widespread activation throughout the entire cortical surfaces (see diagram B).  It was as if a distributed network of neurons across the whole brain was ignited and put on fire by the mere access to consciousness.
The clinical implication of this research has been extended to the diagnosis of conscious state of coma and unconscious state patients using scale recorded Event Related Potentials (ERP), with an accuracy rate of 100% of cases (meaning that all patients identified as being conscious eventually gained their consciousness). The business implication of this research again emphasizes the unique advantage of Sentient’s approach to consumer subconscious research and the recent emerging field of neuromarketing.  Consumers may not know what is driving their behavior, but their brain has it all.

Figure complementary of Dehaene et al.( 2006 ). Conscious, preconscious, and subliminal processing: a testable taxonomy.  Trends in Cognitive Sciences. 10(5), 204-211.
Stanislas Dehaene, Jean-Pierre Changeux, Lionel Naccache, Jérôme Sackur, and Claire Sergent. (2006). Conscious, preconscious, and subliminal processing: a testable taxonomy. Trends in Cognitive Sciences, 10(5), 204-211.

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