When learning about [Operant Conditioning](http://en.wikipedia.org/wiki/Operant_conditioning), I remember being taught that not consistently rewarding the desired behavior could (seemingly counterintuitively) actually *increase* the strength of learning the conditioned behavior. Is this correct?

If this is correct, is it more effective to begin providing a reward at or near 100% of the time the conditioned behavior is performed, and then slowly reduce the amount to a lower percentage? Or is it more effective to simply start with a lower percentage?