Background Noise
CAN YOU HEAR THIS? 
(SFX: TONE) 
CAN YOU STILL HEAR IT? 
(Sfx: tone fades) 
THE NOISE IS STILL THERE--IT'S JUST TOO SOFT FOR YOU TO HEAR.  NOW, WITHOUT MAKING
THE TONE ANY LOUDER, WE'RE GOING TO ADD SOME BACKGROUND NOISE.  CAN YOU
HEAR THE TONE AGAIN?  (Sfx: Tone and background noise.) YOU'D THINK THAT ADDING
NOSE WOULD MAKE IT EVEN HARDER TO HEAR THE TONE, BUT IT TURNS OUT THAT'S NOT
TRUE. 

MOSS: "It's a non-intuitive idea, from time immemorial, people have always thought htat
adding random processes or noise. . .only degrades the information content."

FRANK MOSS IS A PROFESSOR OF PHYSICS AND BIOLOGY A THT EUNIVERSITY OF MISSOURI,
AND HE SAYS OUR BRAINS ONLY HEAR A NOISE WHEN IT REACHES A CERTAIN LOUDNESS--SO WHEN WE PLAYED THE SOFT TONE YOUR BRAIN DIDN'T REGISTER IT.  BUT ADD NOISE
AND THE TWO SOUNDS TOGETHER BECOME LOUD ENOUGH FOR YOU TO HEAR.  MOSS
THINKS ANIMALS HAVE EVOLVD TO MAKE USE OF THE FACT THAT OUR WORLD ALWAYS
HAS LOTS OF BACKGROUND NOISE--AND NOT JUST FOR THINGS LIKE HEARING.  A
CRAYFISH, FOR EXAMPLE, SENSES PREDATORS MOVING THROUGH THE WATER WITH LITTLE
HAIRS ON ITS TAIL.

Moss: "These hairs move with the water and as a predator approaches it sets the water
into certain kinds of motion but if you don't move the hair enough . . the sensory neuron
will not fire.  There's water turbulence all around them and we believe that this
background noise can be made use of in the detection of predators."