Not to prolong this thread, but I thought I'd add to the whole perception thing. As humans we're seriously prone to suggestion, perception and conditioning. Just to show an example of this, here's a picutre that will demonstrate how easily we can be deceived visualy.
http://members.lycos.nl/amazingart/images/adelson_checkershadow.jpg
Note: belive it or not, squares A and B are exactly the same color.
Now all of us "see" those as different colors, just like someone may "hear" a change in a speaker after a period of time. But it can be scientifically proven that those squares are the same color as well as the fact that the sound doesn't change in a speaker.
