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Comment by amelius | Hacker News Reader

I found this to be insightful:

> ... human neurons are slow yet humans can perform lots of complicated tasks in a fraction of a second. More specifically, it is well-known that a human neuron fires no more than 100 times per second. This means that, if a human can solve a problem in 0.1 seconds, then our neurons have enough time to fire only 10 times --- definitely not much more than that. It therefore follows that a large neural network with 10 layers can do anything a human can in 0.1 seconds.

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This seems wrong. My understanding is that the ~200 spikes/second limit derives from the cell needing to "reload" before firing again, rather than some built in latency. Relaying a spike can be very quick indeed. A better conclusion would be that we don't have time for too many recursions in that short a time. Also, I can't think of any particularly hard problem that humans can solve in 0.1 seconds (see e.g. http://en.wikipedia.org/wiki/Hick%27s_law)

> Also, I can't think of any particularly hard problem that humans can solve in 0.1 seconds

Recognizing someone is a hard problem that most humans can do efficiently (except me maybe)

I actually came in here to ask for clarification on this.

This sounds presumptuous. Couldn't there be thousands of neural networks which all receive an input signal, and we know how to interpret the output of all of these, as a signal. Maybe the neural networks themselves are all only 10 layers deep, but if they're all running in parallel - this defeats this point, right?

I don't really know anything about it, though.

Combining a thousand networks into one signal is effectively one extra layer (though I don't think human neurons can actually handle a thousand incoming connections).

The observation was a comment on how deep a network needs to be to perform useful tasks.

Humans have >10^14 synapses and slighly short of 10^11 neurons. Neurons thus have more than thousand incoming connections on average.

Purkinje cells can have on the order of hundreds of thousands of inputs.

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