Scientists have recently discovered intriguing insights into how our brains process vocal emissions, uncovering the remarkable ability to differentiate between the vocalisations of certain primates. This research, conducted by the University of Geneva (UNIGE), challenges previous assumptions and reveals the complex factors that influence our understanding of primate sounds.
Contrary to popular belief, the study found that our ability to identify vocalisations is not solely determined by our genetic proximity to other species. The team from UNIGE asked volunteers to categorize the vocalizations of three species of great apes (Hominidae) and humans, while measuring their brain activity during each exposure to these intriguing sounds.
The results of the study, published in the journal Cerebral Cortex Communications, were astonishing. It was discovered that alongside phylogenetic proximity, the acoustic proximity - the specific frequencies emitted - also plays a crucial role in our ability to identify vocalizations accurately. This finding highlights how our brain has evolved to efficiently process the vocal emissions of our closest primate relatives.
"Our ability to process verbal language extends beyond just semantics. Other parameters, such as prosody and affective bursts, contribute to the meaning and understanding of our vocal communications," explains Leonardo Ceravolo, senior lecturer at UNIGE's Faculty of Psychology and Educational Sciences, and the first author of the study.
To conduct the research, a group of 25 volunteers were placed in an MRI scanner and equipped with headphones. They were exposed to various vocalizations from humans and three primate species: chimpanzees, macaques, and bonobos. The participants were then tasked with categorizing the vocalizations to identify the species they belonged to. The vocalizations ranged from positive interactions to threats or distress calls.
The results showed that when exposed to chimpanzee and macaque vocalizations, the frontal and orbitofrontal regions of the participants' brains were activated in a similar way to human vocalizations. Remarkably, the participants were able to differentiate between these primate sounds with ease. However, the activation of these brain areas was significantly reduced when confronted with the vocalizations of bonobos - another close cousin of humans. Categorization of bonobo vocalizations was at chance level, indicating a distinct challenge in decoding their sounds.
Bonobo
Didier Grandjean, full professor at the Swiss Center for Affective Sciences and at UNIGE's Faculty of Psychology and Educational Sciences, who led the study, explains, "Our results show that a second parameter comes into play: acoustic distance. The further the dynamics of the acoustic parameters, such as the frequencies used, are from those of humans, the less certain frontal regions are activated. This acoustic distance, in terms of frequencies, explains our inability to decode bonobo vocalizations, despite their close phylogenetic proximity."
This study provides a glimpse into the fascinating world of primate vocal communication and how our brains process these intricate sounds. The next phase of research will delve deeper into identifying the emotional content of vocalizations emitted by chimpanzees, macaques, and bonobos, shedding further light on the complexities of primate communication.
