Each individual creates his own personal umwelt, full of objects with special meaning to him. You can most clearly see this last fact by letting yourself be led through an unknown city by a native. He will steer you along a path obvious to him, but invisible to you. But the two of you share some things: neither of you is likely to stop and listen to the ultrasonic cry of a nearby bat; neither of you smells what the man passing you had for dinner last night (unless it involved a lot of garlic). We ... and every other animal dovetail into our environment: we are bombarded with stimuli, but only a very few are meaningful to us.