sorry for posting twice in this thread but i figure it's a good place to ask: what other methods are there for getting a nn to report "i don't know"
The gist is, you train a single classifier that will work as two classifiers (with certain restrictions): one that says "false/not-false" and another that says "true/not-true".
If the output of the classifier is "not-false" and "not-true", then you consider that as a "I don't know".