ABSTRACT
INTRODUCTION You are sitting in an airport lounge when a string of sounds reaches your ear. You automatically distinguish them from musak, from the air conditioning, from the sound of a plane landing. They are in an entirely different category, one which human beings label speech. You respond to the string of sounds by getting up and walking towards Gate number 6, where your flight to Cairo is waiting. Looking around you, you see that other passengers are behaving likewise.
