Top positive review
8 people found this helpful
Important role of consciousness
on 3 May 2014
Dehaene describes the extent of unconscious processing. An input can be unconsciously processed to an advanced level, and what comes into consciousness is a small and heavily edited version of the original stimuli. He does not, however, see this as justifying the claim that everything is performed by the unconscious. He views consciousness as having been selected for its specific functions. He envisages a natural division of labour between unconscious and conscious processing. This is related to the necessity when acting in the world, to move from balances of probability in the unconscious, to decision taking at the conscious level. Unconscious information is transient whereas conscious information is more stable. One function of consciousness is to create stable images as the basis of decision taking. The stimuli can therefore be evaluated, used to plan actions, and memorised for future use.
Unconscious stimuli propagate a long way into the brain, but are amplified when they move into consciousness, boosting activity in the parietal and frontal regions. Substantial changes in the higher visual areas were apparent whenever consciousness was reported. The level of activity could rise as much as twelve-fold. In contrast, a wide range of frontal and parietal areas remained inactive if the stimuli were unconscious. Unconscious stimuli are active in the early visual cortex, but lose strength as they progress through the cortex. On the hand, conscious stimuli pick up strength as they progress.
Many neurons in the anterior lobe respond only to when specific features, such as particular people or buildings are consciously perceived. So the move into consciousness is not brain-wide, but relates to specific neurons. The regions of the brain that correlate to consciousness have important differences in their physical structure. Pyramidal neurons with giant cell bodies, supporting dense dendrites with abundant spines and long axons, are concentrated in layers II and III of the cortex. These layers are thicker in the consciousness-related brain regions such as the prefrontal, cingulate and temporal cortex. These regions have also been suggested to contain the brain's main hubs of interconnectivity.
Dehaene effectively disposes of the idea that consciousness is something unimportant. However, there is still no suggestion as to why the processes described in the more frontal brain regions are experienced subjectively, as opposed to being just a more powerful type of unconscious processing from that present in the earlier parts of the cortex.