Imagine two metronomes: one ticking with each beat evenly spaced and the other clicking with a messy, inconsistent rhythm. Most people would find the second metronome to be out of place. But would an animal be able to say the same thing?
A recent study shows that the ability to recognize rhythm may be intrinsic not only to humans, but also to other species of vocal learning. The study suggests that male zebra finches could serve as an ideal animal model for understanding rhythm perception, which may ultimately provide information on speech and movement disorders in humans.
Zebra finches, like humans, can recognize a frequently repeated rhythm over time, according to the study published in August in the Proceedings of the National Academy of Sciences. Aniruddh Patel, cognitive psychologist at Tufts University and co-author of the study, explained how this phenomenon works in humans.
âIf you feel a beat in music, it’s very natural to – without even wanting or planning it – to implicitly start predicting when the next beat is going to come,â Patel said. âIt’s actually what gets you moving and dancing to the music.
The researchers predicted that vocal learning species are more flexible than vocal non-learners in distinguishing rhythmic patterns. In voice learners, the areas of the brain that perceive rhythm and control movement are strongly linked.
“Species [that] have learned that their songs should listen and imitate, so they have these strong connections between hearing and complex movement[s] that are learned, âPatel said.
Mimi Kao, a neurobiologist at Tufts and co-author of the study, said songbirds share similar traits to humans in the learning and processing pathways of vocalizations.
“[The] The key is that songbirds have specialized areas in their brains to learn songs and produce them, âKao said. “Like humans, they have a high level[s] cortical control over their vocalizations, which I think has yet to be found in monkeys.
In the experiments, the researchers first trained the male zebra finches to recognize easy songs so that the finches could learn to distinguish between “isochronous” and “arrhythmic” patterns. Isochronous sounds have equal time between them, while arrhythmic sounds are projected at irregular intervals. An isochronous sound would be like the ticking of a metronome, while arrhythmic sounds can be heard in unpredictable patterns.
During the training phase, finches were rewarded when they pecked a switch after hearing an isochronous pattern. If the stimulus was arrhythmic, the finches weren’t supposed to respond at all. If the birds pecked at the switch after hearing an arrhythmic sound, they were given a time-out as punishment, indicating the response was incorrect.
After two phases of training with different sets of songs, seven out of ten zebra finches were able to tell the difference between isochronous and arrhythmic patterns with 84% accuracy in the initial workouts. Once the finches familiarized themselves with the device, the researchers introduced new isochronous and arrhythmic stimuli over a wide range of new tempi to see if the finches could still detect isochronous sounds. They found that the finches were still able to distinguish the differences.
According to Kao, the most difficult part of working with birds was conditioning them to behave according to the experimental design and motivating them to perform specific tasks.
âSometimes I think there’s a lot of animal cognition where animals know more than we think,â Kao said. âAs humans, we don’t always know what is the best wayâ¦ to ask animals to reveal what they can perceive. “
Kao also observed various personalities in the finches she worked with.
âThere might be a period when they can’t start another try and some birds would just physically walk awayâ¦ and others would wait,â Kao said. âThere are certainly individual differences: ‘Are you a restless animal who moves away or one who can sit patiently?’ “
EnikÅ LadÃ¡nyi, linguist and cognitive science researcher at Vanderbilt University, recalled that finding an animal model to map the mechanisms involved in speech can help research on speech and language disorders, including dyslexia, stuttering or impaired language development.
“These findings and the growing literature on the strong links between rhythm and spoken language processing suggest that alteration of the same neurological mechanism may underlie both arrhythmias and speech or language disturbances,” a LadÃ¡nyi said. “An animal model that shares crucial characteristics with human auditory processing could greatly facilitate our understanding of these mechanisms, [which] can then help identify, treat or even prevent these disorders more effectively.
Jennifer Zuk, a speech therapist at Boston University, suggested that the study’s results can be applied to learn more about rhythm in early brain development.
âTo date, the neural mechanisms underlying the development of typical and atypical rhythm processing abilities in humans have not yet been specified,â Zuk wrote in an email to The Daily. “[The study] holds the promise of the potential to uncover the neural basis of rhythm perception relevant to humans by studying the learning process in zebra finches.