Your brain will take repetitive sounds and turn them into musical passages, and it prefers to group the sounds into repeating pairs. Even if the first note of the pair is the exact same as the second note, your brain will assign two different tones and two different amplitudes (volume) to each.
Think you’re immune? Run out to your car for a minute. Turn the car on and turn the turn signal on. Now listen to the sound your turn signal makes: BLINK er BLINK er BLINK er. Now start saying the words aloud in time to the turn signal, but say this instead – BLINK er BLINK BLINK er BLINK BLINK er BLINK. After a while, with a little concentration some of the BLINKs will turn into er’s and some of the er’s will turn into BLINKs. If you’ve really concentrated, that pattern will continue after you stop coaching yourself out loud. But don’t be too smug, within seconds your brain will get back to making your turn signal into that catchy little ditty you’ve grown to love and accept as reality.
Regardless of what your brain thinks, the clock makes one sound – TICK. But since your brain likes to organize repeating sounds into musical passages, you hear TICK-tock TICK-tock. Typically the second tone in a repeating pattern is assigned a lower pitched note by your ever helpful brain. But try this as you listen: say tick-TOCK-tick tick-TOCK-tick out loud as you listen and you will begin to hear some of the ticks turned into TOCKS and vice-versa. Once you have the hang of it, just repeat tick-tick-tick and eventually you will see that the clock only makes one sound – tick.
Studies have shown through experiments where subjects were wired up to EEG machines that almost universally the human brain puts repeating tones into pairs and that there is more activity in the brain on the first note of the pair. That emphasis – or accent – results in the second note seeming to have a lower tone.
So even though clocks and turn signals all produce identical notes in pitch and volume, our brains make little musical passages for us, and after all, a clock that goes tick-tock is far more romantic (and less aggravating) than a clock that just goes tick-tick-tick-tick-tick-tick-tick-tick-tick-tick-tick…