Are humans the only ones who recognize musical melodies, whether they are played on different instruments, frequencies and tempos? Study reveals that rats showed sensitivity to track harmonic and temporal patterns in music and such sensitivities might be shared across species.
Have you noticed that at birthday parties, the “Happy Birthday” song is sung by different people (with different individual voices) in different frequency ranges and at a randomly chosen speed (slower or faster rhythm)? And that, despite this, all the participants in the party are able to recognize the song, even those who only know the lyrics in another language? This happens because we identify a musical excerpt as an object that can flexibly vary in at least three dimensions (pitch, tempo and timbre) without losing its identity.
But to what extent does the biological predisposition of humans to process music emerge from sensitivities already present in non-human animals? With the support of the BIAL Foundation, researchers Paola Crespo-Bojorque, Alexandre Celma-Miralles and Juan Toro joined forces to explore whether a distant non-vocal learner species, the Long-Evans rat (Rattus norvegicus), would be able to detect surface changes in a familiar tune.
In the paper “Detecting surface changes in a familiar tune: exploring pitch, tempo and timbre”, published in the journal Animal Cognition in February 2022, the researchers from Universitat Pompeu Fabra (Spain), Institució Catalana de Recerca i Estudis Avançats (Spain) and Aarhus University (Denmark) explain that, to carry out the study, they used a sample of 40 female rats aging 5-month-old. The animals were familiarized with an excerpt of the “Happy Birthday” song, using the timbre of an acoustic piano. After familiarization, the animals were submitted to three different test sessions with variation in pitch (higher and lower octave transpositions), tempo (double and half speed) and timbre (violin and piccolo).
The results showed that the rats responded differently to the familiar and novel version of the tune when it was played on new instruments (timbral change) but did not respond differently to the original song and its novel versions that included octave transpositions and changes in tempo. The researchers then concluded that, like humans, rats can recognize a melody, even if it is presented at different frequencies and speeds.
The fact that they do not recognize the musical excerpt when played on violin or piccolo may be related to the processing of intra-species vocal communication signals. That is, unlike humans, who readily process linguistic information regardless of the speaker's identity, rats may not have this normalization mechanism, so the animals in this study might find it difficult to recognize a melody when different instruments produce it.
“A key question in our study is to understand why rats took variations in tempo and pitch to be less psychologically distant than changes in timbre”, says Juan Toro, stressing, however, that “the results indicate that ability to normalize across surface musical features that is present in humans might partly emerge from pre-existing sensitivities to track harmonic and temporal patterns that are already present in other species”.
Learn more about the project “Biological bases of music cognition” here.
