Music has long been the inspiration for many directions of cognitive science research. Music has a special connection with the brain that makes us ask pivotal questions, such as: How do we know that music is music when we hear it? Why does music evoke emotional responses? And why do we associate Mariah Carey and Michael Bublé with Christmas?
To some, the appreciation of music may seem like a characteristically human value. However, non-human animals do show remarkable abilities to process music. Dogs tend to prefer Mozart over Metallica. Elephants can play harmonicas and drums. Birds sing because they have a song (thank you, Maya Angelou). Check out other ways that animals interact with music here.
Rats (Rattus norvegicus) have also been studied for their cognitive processing of music. Rats can discriminate between songs based on loudness, pitch changes, and melodic organization. However, these are more surface level features that could appear in environmental sounds as well as music. Arguably what makes music music is how the tones are organized in temporal patterns—or the rhythm of the song. In 2019, Celma-Miralles and Toro showed that rats can even distinguish between rhythmically regular versus irregular song patterns.
If you own a rat and would like to play some tunes for him/her, please enjoy this rat-approved playlist.
In a recent study published in the Psychonomic Society’s journal Psychonomic Bulletin & Review, Celma-Miralles and Toro (pictured below and websites here, here, and here) took rat musicology to the next level. In their experiment, they asked whether rats could recognize the rhythmic structure of a song independent of pitch or melodic changes.
To test this question, the authors familiarized forty rats with the Happy Birthday song. For this birthday, instead of cake, the rats received food pellets every time they poked their nose into the feeder when the song played. They were thus trained to recognize the Happy Birthday song 40 times a day for 26 days. Imagine listening to your favorite song on repeat for a month. This is what the rats experienced, and it made them proficient at recognizing the song.
After the familiarization phase, they tested the rats in one test session. In this session, they played three excerpts of different versions of the song. These were:
- The familiar Happy Birthday excerpt (that we all know and love)
- An isotonic excerpt, which is the same rhythm as before, but uses a constant pitch
- A rhythmically-scrambled excerpt, which uses the same melody but in different rhythmic order
Familiar:
Isotonic:
Rhythmically-scrambled:
During this test session, the rats responded to the three excerpts differently. They gave the nose-poking response to the rhythmically scrambled version more than the other two. The familiar and isotonic versions did not differ in their amount of subsequent nose-poking. Keep in mind that the familiar and isotonic versions had the same rhythmic structure. Therefore, the rats seemed to be discriminating song excerpts on the basis of rhythm rather than pitch differences.
Based on the overall rat responses, they were more sensitive to rhythm than other features in the song excerpts. This demonstrates that the rats could recognize the tune regardless of the pitch of the tones. They acknowledge that there were individual differences in how the rats processed the excerpts because eight of the forty rats gave more nose pokes to the isotonic version, indicating a sensitivity to pitch changes. While there could be some differences among the rodents, they most often tended to focus on the rhythmic structure of the song.
This finding shows that rats’ ability to process music goes beyond the surface level features of sounds (e.g., pitch and loudness), and they can actually distinguish a rhythmically complex auditory signal. This is an impressive result because it suggests that the cognitive processes involved with music perception have deep biological roots that span across species.
Ultimately, whether you’re a human or a rat—in the immortal words of Gloria Estefan—the rhythm is gonna get you.
Psychonomic Society article featured in this post:
Celma-Miralles, A., & Toro, J. M. (2020). Non-human animals detect the rhythmic structure of a familiar tune. Psychonomic Bulletin & Review. https://doi.org/10.3758%2Fs13423-020-01739-2