Levels

[Terry Sejnowski]

There are at least three notions of levels that are commonly used
to discuss the brain.  Marr introduced levels of analysis --
computatonal, algorithmic, and implementational, and thought they
were independent of each other.  In biology there are well defined
levels of organization: molecular, synaptic, neuronal, networks,
columns, maps, and systems.  These can be characterized anatomically
according to their spatial scale.  Finally, one can distinguish 
levels of processing, from the sensory periphery toward higher
processing centers.  Although these centers can be ranked in a
hierarchy according to latency, feedback connections allow information
to flow in both directions.

For a more detailed discussion on these three types of levels, and
references, see Churchland and Sejnowski, Perspectives on Cognitive
Neuroscience, Science 242, 741-745 (1988).

Terry

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