Reference: Crespo‐Bojorque, P., Celma-Miralles, A., & Toro, J. M. (2022). Detecting surface changes in a familiar tune: exploring pitch, tempo and timbre. Animal Cognition.

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If you enjoy listening to music, there are many songs that you would recognize even if they are sped up, slowed down, played at a higher or lower pitch, or on a completely different instrument. You might remark on these surface-level differences, but you would still recognize the same fundamental melody.

The ways that people create, enjoy, and share music are dependent on this tendency to recognize a particular tune regardless of changes in pitch (frequency), tempo (speed), or timbre (sound qualities that differentiate instruments). Without this ability, someone who overheard a friend whistling a familiar song might interpret it as an entirely new piece of music. Or potentially, no one would ever whistle a song at all because the sound of their whistle would be too different from the original instruments, rendering the tune completely unrecognizable.

This ability to recognize melodies may have originally evolved to help us understand acoustic, or sound-based, communication. Understanding speech requires recognizing that the information conveyed remains the same even if words are spoken by different voices or at different speeds. If this evolutionary hypothesis is correct, then animals with different ways of communicating might also differ in how they recognize music.

Studying music recognition in rats

In a recent study published in the journal Animal Cognition, a team of psychologists investigated the degree to which rats can recognize altered melodies. They first trained the rats to recognize the tune of the “Happy Birthday” song played on a piano. After the researchers played the song, the rats could poke a button with their nose and receive some tasty treats. Soon, the rats learned to poke the button whenever they heard the song play.

After this training stage was complete, the researchers played modified versions of the tune to see if the rats responded with as many nose pokes as they did to the original version. To test the effects of changing the tempo, the researchers made a fast (double speed) version of the song and a slow (half speed) version. To test changes in pitch, they transposed the song an octave higher and an octave lower. And to test changes in the song’s timbre, they used computer software to create piccolo and violin versions of the song to contrast with the original piano version.

During these tests, the rats had a similar number of nose-poke responses to the faster, slower, higher-pitched, and lower-pitched songs as they did to the original. But when the song was played on a different instrument, the rats’ nose poke responses decreased. Regardless of whether it was played on a piccolo or a violin, the rats seemed to interpret the new version of the melody as fundamentally different from the original version, which was played on a piano.

What do these findings mean for rats… and for humans?

The ability to recognize a melody despite changes in pitch and tempo may be important for acoustic communication in rats just like it is in humans. In addition to using smell and body language to communicate, rats also produce ultrasonic vocalizations that are too high-pitched for humans to hear, but are critical to rat social interactions [1]. Across individuals, rats may differ in their vocalization speed, similar to how some people talk faster than others. Furthermore, male rats tend to vocalize at lower frequencies than female rats [2]. This variation means that rats need to be able to filter out differences in speed and frequency to be able to accurately interpret what other rats are saying to them.

In contrast to humans, rats did not recognize a familiar song when it was played on a new instrument. Previous research has shown similar results for some songbirds as well [3,4]. These findings suggest that for some animals, differences in timbre may convey distinct information, similar to how different words have different meanings in human communication. This would explain why the rats reacted differently to the same melody played on a piano and a violin.

But for humans, ignoring timbre changes may be critical to understanding spoken words across a wide range of voices. People differ widely in their voice and speech characteristics, but to communicate effectively, we need to latch onto the key information: the words being spoken. This ability to separate signal from noise in our spoken communication likely translated into creating and recognizing musical melodies as well.

Of course, more research is needed to explain exactly how speech and music have changed over time and possibly influenced each other throughout our evolutionary history. And more studies like this one could also help us understand how other animals communicate with each other and interpret the sounds around them.

Additional References:

1. Brudzynski, S. M. (2013). Ethotransmission: Communication of emotional states through ultrasonic vocalizations in rats. Current Opinion in Neurobiology, 23(3), 310–317.
2. Lenell, C. & Johnson, A. M. (2017). Sexual dimorphism in laryngeal muscle fibers and ultrasonic vocalizations in the adult rat. The Laryngoscope, 127(8), E270–E276.
3. Bregman, M., Patel, A. D., & Getner, T. (2016). Songbirds use spectral shape, not pitch, for sound pattern recognition. Proceedings of the National Academy of Sciences, 113(6), 1666–1671.
4. Hoeschele, M., Cook, R. G., Guillette, L. M., Hahn, A. H., & Sturdy, C. B. (2014). Timbre influences chord discrimination in black-capped chickadees (Poecile atricapillus) but not humans (Homo sapiens). Journal of Comparative Psychology, 128(4), 387–401.

Images: (1) Rat photo by Alexandr Gusev, Unsplash, (2) Instrument photos modified from Wikimedia Commons.