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Looking further into the question, of how there can be an input with out a resulting output, I found myself looking at the more biological aspect behind the nervous system. I think that such an occurance can occur if the input does not generate enough of a stimulus to result in an action potential, that goes above a threshold value. For an output to be generated, there has to be a strong enough action potential. So there may be an input that isnt strong enough to cause a reaction/output. Otherwise an organism would constently be reacting, and having an output for every small input that occurs.

Looking at the same question in a different manner, explaining the presence of an output with out an input, is still unclear to me, unless the inputs are so insignificant, that we do not realize them, or the inputs could be internalized and something that we can not obviously recognize as an input.