  The relationship between brains and computers is often taken to be merely
metaphorical. However, genuine computational systems can be implemented in
virtually any media; thus, one can take seriously the view that brains
literally compute. But without empirical criteria for what makes a physical
system genuinely a computational one, computation remains a matter of
perspective, especially for natural systems (e.g., brains) that were not
explicitly designed and engineered to be computers. Considerations from real
examples of physical computers-both analog and digital, contemporary and
historical-make clear what those empirical criteria must be. Finally, applying
those criteria to the brain shows how we can view the brain as a computer
(probably an analog one at that), which, in turn, illuminates how that claim is
both informative and falsifiable.
