Hands up if all you were taught in school was that the dude rang a bell, fed the dog and so whenever the dog heard the bell at a later date, the dog salivated...
Pavlov found that a dog could be conditioned to salivate when a metronome beat at 60 beats per minute. The same dog could be conditioned to exhibit the exact opposite behavior (no salivation) when the beat was raised to 120 beats per minute. So, what happened to the dog when a metronome beating 60 beats per second was played at the same time as a metronome beating at 120 beats per second?
In another experiment with the same dog, Pavlov had both metronomes beating at the same time, one at 60 beats, the other at 120 beats per minute. The conditioned dog was required to do two totally opposite functions at the same time. This produced nervous shock, and the dog collapsed, unconscious.
Next, with the same dog, Pavlov had the 60-beat metronome suddenly jump to 120 beats per minute. At the same instant, the 120-beat metronome dropped to 60 beats per minute. This produced a melodic dissonance. When the metronomes were switched back and forth rapidly, the dog became so distressed that it died. In communist Russia, these experiments were then extended to humans, with similar results.