TIP: although you can use the speakers on your multimedia computer, a Make sure the volume isn't too loud!
Say the words "college ecology" aloud ten times. If anyone notices, give them a confident look and tell them that you're performing an experiment. Go ahead and try it........................
After a while you find yourself saying "collegey, collegey, collegey." What's going on? Your brain grouped the sounds according to rules that we haven't quite figured out yet.
The illusion you're about to listen to does the same thing.
Now each instrument will alternate tones creating a single, combined pattern. As the speed increases what happens?
How many speed increases did you hear?
At what point did the instruments begin to separate into two melodic patterns?
Listen to the combined streams a second and third time. Do the instruments separate at the same place every time?
What's the point?
Did you know that you process most of your auditory information in the temporal lobes of your brain? That's right and you actually have two of them, one on each side brain, close to your ears. [ They're not really blue – they're grey, we just did that to make it easier to point out. ]
The point here is at the slow speed most people can hear a single rising pattern created by a combination of the two instruments. This is called temporal coherence and happens because your brain normally groups sound in similar frequency ranges together into single patterns.
By the final speed increase, you should hear two descending patterns emerge, one unique to each instrument. Both may be difficult to listen to at the same time, try listening to one ear and then the other. This is called fission and is the result of your brain's ability to distinguish different sound textures within similar frequency ranges.
Just for Fun!
What do you think will happen if we use two instruments that have very different sound textures, say a muted trumpet and a marimba?
What other experiments might you try?
"'I weep for you,' the Walrus said:
– Lewis Carroll
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