When you hear a cover of a familiar song, you likely still recognize the song, even if it’s suddenly in a different tempo, an octave higher or played on different instruments and sung by a different singer. How does that work? To find out more about the way humans recognize music, researchers in Barcelona did an unusual experiment: they made rats listen to the “Happy Birthday” song.
You’ve probably heard the song “Happy Birthday” dozens of times, either awkwardly waiting for everyone to sing it on your birthday, or while singing it for others, or in films or TV shows (at least since it became free of copyright in 2016). Even without the context of a birthday, you knew which song it was every time you heard it – with or without music instruments, slightly off key, sung way too high or too low for you to manage, or even those times when someone started it much too slow. But could you do that if you were a different species?
To understand how humans are able to recognize songs even as covers, Juan Manuel Toro and his colleagues at the Universitat Pompeu Fabra in Barcelona, wondered how much of this skill is shared with other species. They tested this by playing a piano version of the second half of the “Happy Birthday” song to forty rats for ten minutes every day, for three weeks. Despite it not being any of the rats’ birthdays (they were all five months old at the time of the study) they heard this same tune over and over, forty times in a row, for days at a time just to get them familiarized with it.
Importantly, every time they heard the song, they also got a snack. Eventually, hearing the tune primed the rats to expect their snack, just like you would expect to get cake if you hear people singing “Happy Birthday” in the office break room.
After the training period, the rats suddenly got to hear a variation of the original tune. They either heard it faster or slower, at a higher pitch or a lower pitch, or the same melody played on a different instrument (violin or piccolo instead of piano). If they thought it was still the same song, they would behave as if they were getting their snack by poking their nose on the feeder, so this allowed the researchers to see whether the rats recognized the variations.
According to this study, published in the journal Animal Cognition, the rats still recognized the song if the pitch or tempo was changed, but once it was played on another instrument, they no longer responded to it. That’s interesting, because it shows that some part of our human music recognition is not uniquely human.
“The results suggest that the ability to recognize patterns over changes in pitch and tempo present in humans might emerge from pre-existing abilities in other species,” Toro told the Universitat Pompeu Fabra.
Of course humans can identify much more complex variations than rats, so that we even recognize a tune if it’s played on different instruments. But this study suggests that that ability evolved more recently than the ability to match a tune across different pitches or tempos. It’s another piece of the puzzle of human music perception. And it’s something to think about the next time you find yourself singing “Happy Birthday” in anticipation of cake.