Recent studies have shown that we can consciously and subconsciously physically manipulate the position and directionality of our outer ear and some of the mechanics in the inner ear to "zero in" on noises and affect the frequency response of the ear. Our ears move imperceptibly when we look from side to side to synchronize what we hear with what we see. Try listening to one person in a busy room is saying then try doing the same while looking somewhere else.
There is hardware actively filtering out interfering sounds based on location and frequency, then there's the wetware that further processes the incoming signals and attempts to strip unwanted noise. I don't believe the second can be effectively done without a feedback loop to the first.