For those who haven't heard the famous "infinitely ascending/descending tone", please listen to it now on the Wikipedia page: http://en.wikipedia.org/wiki/Shepard_tone. Although the Wikipedia version is unable to demonstrate this, one can download similar sounds and play them in a loop and the tone will seem to continue ascending or descending forever (here's a classic ascending tone to download if you want to try it). As one listens, it seems impossible that it could continue going in that direction without leaving the range of human hearing. Surely it's going to have to end some time! Yet it never does.
How does it work? There are simply overlapping tones; in a descending scale, these travel downward together, but at different octaves. When one tone reaches the bottom, it fades out and fades back in at the top of the scale. The ear initially latches onto the main (loudest) tone and follows it down, but our brains eventually play a trick on us and swap that tone out for the next descending tone as the first fades away, giving the illusion of a single descending tone.
If one listens to it long enough, however, one can learn to hear the distinct tones and can detect a new tone fading in at the top of the scale. This breaks the illusion. It requires either a receptive mindset, or ignorance of how the sound works, in order to sustain the illusion. Trained musicians may fail to be fooled by the sound from the very beginning.
I think the application is obvious: Witnesses always believe that the end is Very Soon Now. It's easy to find evidence that the world is getting worse -- the latest evidence is school shootings. Before that it was what, the collapse of various national economies? Before that maybe it was 9/11? Sometimes the evidence is something specific to an individual's life, a hard time they're going through. But no matter how many decades The End seems to delay, it's always close, and getting closer. Many older Witnesses can be heard stating this. They've never been more sure that Armageddon is coming soon. Our tendency may be to accept their experienced opinion at face value.
But when the latest impending disaster passes, or fades away, do we recognize that it's gone, or do we simply look for a new disaster to latch onto, as evidence for our beliefs? Do we extrapolate from specific day-to-day problems? "That customer service person didn't know what they were talking about, what is this world coming to? How does anybody do their jobs anymore? It's a wonder this world can keep on going at all!"
And are we willing to see trends that are going in the opposite direction? What about the massive improvements in health care over the last century, leading to a huge drop in infant mortality? Declining poverty and increasing life expectancy? What about the fact that overall violence has decreased in many societies? An increasing awareness of human rights, animal rights, ecological preservation, etc.?
The real picture is more complex than a simple downward spiral. There have been people lamenting a downward trend in the world for centuries, perhaps thousands of years, and yet, like the Risset scale, it can't actually go downward forever, or it would have reached the bottom long ago. This skewed view of reality, where we only emphasize the negative, is not peculiar to Witnesses. Many people feel this way, and end up reinforcing each others' beliefs, but this is a shared feeling not based in fact, but emotion. The 24-hours news channels, which endlessly repeat the same bad news but fail to devote much time to covering positive long-term trends and solved problems, also share some blame for this attitude in society.
But let's not confuse prevailing attitudes with the facts. The world is largely what we make of it. We can choose to see only decline, and then The End seems to always be around the corner... then again, some people only want to see the positive things in life! I think we can agree the ideal place is somewhere in the middle where we recognize that there are still serious problems in the world, but where we also spend time reflecting on the positives in our world, our society, and our personal lives. Don't fall victim to the real-life version of the Shepard Scale!