"By 2023, a $1,000 computer will exceed the computation capability of the Human Brain."
How to quantify the 'computation capability' of the human brain? If we knew the transformations the brain makes to the information it receives, we would understand the brain, which we do not.
The estimates of the brains equivalent computational capacity I have read use functional models of regions of the brain, (i.e. audio, visual, ...) to obtain an estimate per neuron and extrapolate that to the entire brain. Estimates are 10e14 to 10e15 operations per second.
See http://books.google.com/books?id=88U6hdUi6D0C&pg=PA122&#...
However -- the neural functions cited by Kurzweil for which 'operations per second' have been estimated are:
1) edge and motion detection in the retina
2) computation of time delay between a sound arriving at one of our two ears versus the other
3) silicon computations required to model 10e4 cerebellar neurons
Let's throw out (3), since it's hard to know from the quick mention he gives what 'model' means in this context.
Now consider (1) and (2): they represent specialized, if experimentally accessible computations. The relationship of operations in the retina to operations in the cortex is unknown. (It seems, actually, that cortex reimplements certain retinal functions, e.g. directional selectivity, for unknown reasons.) Similarly, IIRC, the time difference between a sound arriving at the two ears is thought to be computed by the olivary nucleus (http://en.wikipedia.org/wiki/Superior_olivary_nucleus), a specialized brainstem structure.
So what do the retina and the brainstem have to do with the cortex? Even if you accept (3), you can ask the same question about cerebellum.
In the link you give, Kurzweil says that these studies show that "it is clear that we can emulate the functionality of brain regions with less computation than would be required to simulate the precise nonlinear operation of each neuron and all of the neural components (that is, all of the complex interactions that take place inside each neuron)."
I hope he's right; but the evidence he gives is pretty thin.
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