It is quite simple to understand the concept of lateral localization of sound. It depends upon the loudness and time (and wave phase) difference between 2 ears.
But how can we detect front-back localization (if someone is calling me from my front/back direction) and up-down localization (such as an aeroplane's sound is coming from upper place and a car's whistle is coming from lower-direction of the balcony I'm standing). How does that happen? Or doesn't localization happen at all under these conditions? Is it just an illusion just because we are already aware about the possible source (such as since it is aeroplane's sound then it might coming from upward place, or I can see my friend is talking by standing my front so the sound must coming from front... etc.)
I've searched wikipedia and other sites, but I found nothing that explained the matter sufficiently.