Several aspects of human cognition are particularly suggestive of the kinds of neural mechanisms described in this text. We briefly describe some of the most important of these aspects here to further motivate and highlight the connections between cognition and neurobiology. However, as you will discover, these aspects of cognition are perhaps not the most obvious to the average person. Our introspections into the nature of our own cognition tend to emphasize the ``conscious'' aspects (because this is by definition what we are aware of), which appear to be serial (one thought at a time) and focused on a subset of things occurring inside and outside the brain. This fact undoubtedly contributed to the popularity of the standard serial computer model for understanding human cognition, which we will use as a point of comparison for the discussion that follows.
We argue that these conscious aspects of human cognition are the proverbial ``tip of the iceberg'' floating above the waterline, while the great mass of cognition that makes all of this possible floats below, relatively inaccessible to our conscious introspection. In the terminology of RumelhartMcClelland86, neural networks focus on the microstructure of cognition. Attempts to understand cognition by only focusing on what's ``above water'' may be difficult, because all the underwater stuff is necessary to keep the tip above water in the first place -- otherwise, the whole thing will just sink! To push this metaphor to its limits, the following are a few illuminating shafts of light down into this important underwater realm, and some ideas about how they keep the ``tip'' afloat. The aspects of cognition we will discuss are:
Lest you get the impression that computational cognitive neuroscience
is unable to say anything useful about conscious experience, or that
we do not address this phenomenon in this book, we note that
chapter 11 deals specifically with ``higher-level
cognition,'' which is closely associated with conscious experience.
There we present a set of ideas and models that provide the bridge
between the basic mechanisms and principles developed in the rest of
the book, and the more sequential, discrete, and focused nature of
conscious experience. We view these properties as arising partly due
to specializations of particular brain areas (the prefrontal cortex
and the hippocampus), and partly as a result of the emergent
phenomena that arise from the basic properties of neural processing
as employed in a coordinated processing system. This chapter
emphasizes that there is really a continuum between what we have been
referring to as conscious and subconscious processing.