INTERNAL CONTEXT AND TOP-DOWN PROCESSING

Recent experimental work suggests that the concept of contextual field s should be generalized to allow the modulation of local information e xtraction by both external and internal context. The external context relates to the coherent information of the stimulus; the internal cont ext refers to the parts of this information which are relevant for beh avior. This dual interaction, present at every level of the hierarchy, requires a fundamental unit of processing more complex than a single neuron appears today. We argue that the cortical column supplies the r equired mechanisms for a separate top-down and bottom-up processing an d allows for interaction without destructive cross-talk. This flexibil ity might explain why the same basic architecture of a cortical column is used in the whole isocortex.