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   I disagree that the CNS is a set of input/output boxes capable of generating outputs on its own. I believe that there have to be stimlui present in order for an output to occur. Now, it could be possible that the input box does not appear full on the conscious level, however there could be a stimuli which fills the input box on the subconscious. Because human beings are capable of retaining information (i.e, recall experiences) even though one does not recognize the outside stimuli as such, it still is capable of triggering an output. For example, in introductory psychology class, one is taught to study with the same writing utensil as he/she plans on taking the exam with, or chewing the same scent of gum while studying as one does when he/she takes the exam. The reason behind this, is so that consistency in one's environment will subconsciously trigger one's memory and allow you to recall the infromation that one retains while studying.   Therefore, what may not be recognized as an input can still act as such in a deeper part of the brain.
   In addition, the absence of an input could trigger an output. When you realize that you are thinking of "nothing," essentially this is when thoughts pop into your brain again, and your brain creates outputs, based on your spontaneous thoughts. So, if our CNS is capable of creating outputs, without any inputs, then why does our brain catalog our previous experiences. What is the need for memory?