Turn that song up — evolution made you (and rats!) recognize it

Is that "Human Nature" on the radio? Turn it up, because it really is human nature to tune in. What you might not realize is that you know that song for a reason.

Whether it’s the smooth beats of Michael Jackson or the anxious energy of Psych the Musical, evolution explains why we can perceive and recognize music, even if it’s a cover in a different key, played by a different instrument or sung by a different voice. It isn’t just Homo sapiens. Humans may be seen as unique because of our language and music skills, but there are aspects of our understanding and perception of music that we evolved and share with other species.

This is what researcher Juan Manuel Toro of the Language and Comparative Cognition Group (LCC) of the Universitat Pompeu Fabra Center for Brain and Cognition in Barcelona, Spain, found out after seeing how rats responded to different variations of a tune. We often associate birds with music, but rats? They proved they were able to pick up on Happy Birthday despite changes in speed or tone or timbre. Toro led a study recently published in Animal Cognition.

“Humans process music in a relative, as opposed to absolute, way because we have what is called octave equivalence, that is, the ability to perceive as equivalent notes at different octaves,” he told SYFY WIRE. “This has been linked to linguistic normalization.”

Meaning, we can perceive music apart from changes in timbre (the type of instrument or voice), tempo (speed) or frequency (how often sound pressures repeat, otherwise known as pitch). We speak at different frequencies. Some voices are higher, some lower. Humans are able to recognize a song even when those factors change because the linguistic signal already registers in our brains. This is why you would recognize Happy Birthday whether it was sung by a choir backed by a full orchestra or played on the piano. It is still relatively the same.

Toro and his research team trained rats to identify the same tune you blow out the candles on your cake to. There are 13 tones and a range of pitches in Happy Birthday, which the rats were familiarized with before they were listened to versions of the song in which the frequency, timbre, or speed had been modified in some way. They knew what song it was regardless of the changes in frequency or tempo. It was timbre they had problems with, so it is unlikely one of those rats would have realized it was the same song if you blasted it on an electric guitar.

Humans are thought to perceive music in a relative manner, unlike the more absolute way the rats process it, because of a linguistic signal that has been normalized. It is also possible that we had previously evolved a protolanguage which involved communication that was musical to some extent, so we ended up incorporating that into what would become human language. The way many birds communicate often sounds musical. Some bird and mammal species, including chimps, sea lions, cockatoos and other parrots, perceive shifts in frequency.

“For some other species, octave equivalence is inherent in their own vocalizations,” said Toro. “This is not an ability that has only emerged in humans but more likely co-opted from the normalization of natural vocalizations present across several species, including humans.”

It isn’t just rats that have trouble with timbre. Many other animals are not able to recognize music if whatever is making the sound suddenly changes. Some parrots seem to have no problem with that. There are still some unknowns as to how parrots process music compared to humans. Previous research suggests that they synchronize to a rhythm, then adapt that synchronization to a song’s tempo. Toro thinks it doesn’t hurt that they are amazing vocal learners and imitators.

“More research would be needed to better understand what is the role that timbre might play in parrots’ recognition of tunes, or whether they, like humans, display preferences for certain musical features similarly to what is observed in humans.”

So maybe the perception of music isn’t something that is only human, but still part of human nature.