Page 48 - Summer2022

SOUNDS FULL OF MEANING Later, alternative approaches gained attention. From those, we learn that western lowland gorillas, Gorilla gorilla gorilla, have impressive control over their breath- ing behavior (Perlman, 2017). Perlman reported that Koko, a female gorilla (for information and videos, see bit.ly/3HKY47C), could drink through a straw and used different types of breath signals to communicate her atti- tude. She blew gently onto the face of a person she was fond of and harshly onto someone she did not wish to talk to. Koko not only employed breathing signals but also vocal signals; both were frequently accompanied by gestures (Perlman and Clark, 2015). Works like these might introduce us to the onset of volitional control over vocal behavior. However, it does not stop there. We have known for a few decades that primates, and here we specifically refer to free-ranging East African vervet monkeys, Chlorocebus pygerythrus, have different alarm calls for different predators. A call for an eagle is distinct from a call for a leopard, among other threats and preda- tors (Seyfarth et al., 1980). In the end, hiding from an eagle is different than hiding from a leopard. Even more compelling, however, is the evidence from human-fostered individuals or groups. Kanzi might be the best-known among his species (Savage-Rumbaugh et al., 1986). This male bonobo, Pan paniscus, was taught to communicate with so-called lexigrams, a set of symbols con- veying a certain meaning (Savage-Rumbaugh et al., 1986). Less known, although not less impressive, was his ability to communicate using vocalizations. Kanzi not only used spe- cific vocalizations in different semantic contexts, but he also modified those vocalizations (Hopkins and Savage-Rum- baugh, 1991). His behavior was similar to modulations such as talking with a higher fundamental frequency to express child-directedspeech.Finally,ithaspreviouslybeenshown that both orangutans (Pongo) and chimpanzees (Pan trog- lodytes) are able to develop novel vocalizations to capture the attention of their caretakers (Lameira et al., 2016). Such vocalizations are structurally more like human speech than typical primate vocalizations. All in all, this evidence shows that great apes do not only rely on gestures. They very much strategically use vocal signals, too. According to Slocombe et al. (2011), theoretical approaches in favor of gestures or vocalizations might be biased by empirical work. In a meta-analysis of empiri- cal work carried out between 1960 and 2008, only 5% of the 553 studies on primates analyzed vocalizations and gestures together. In the rest of the studies, researchers focused on one modality only, supporting the respec- tive theoretical view. That means researchers following the gesture-first theory supported their claims with empirical data from gestures but did not challenge it with vocalizations. The same is true for theories focusing on vocalizations, which used empirical data on vocalizations without confronting it directly with gesture data. Another methodological issue is that approximately 90% of the empirical evidence comes from animals in captive environments with all its consequences on, for example, social behavior, motion, and diet. Furthermore, the living environment of the animals is tightly coupled to the objective of the study. For animals recorded in the wild, researchers focus on vocalizations rather than gestures, which is very likely due to methodologi- cal challenges such as the unpredictability of gestures, moving animals, animals interacting within a larger social group, and changes in the camera perspectives. On the other hand, gesture research has often been car- ried out in captive environments such as zoos. These methodological differences led Slocombe et al. (2011) to a call for more multimodal research to substantiate the theoretical approaches. Ten years later, Liebal et al. (2022) conducted a similar meta-analysis across 294 studies published between 2011 and 2020. Although certain research gaps have been closed, Liebal and colleagues reported a significant decrease; only 2% of the studies were multimodal. Pros and Cons for the Role of Vocalizations in Language Evolution The unimodal perspective on the emergence of com- munication has spread across the discipline and affected the view on human communication as well. With hand gestures, one can, for example, indexically refer to spatial locations, iconically imitate actions, and depict shapes and sizes of objects. One argument for gestures as the onset of communication is that it was possible to teach some captive apes American Sign Language but not spoken communication. Another frequently noted fact is that gestures facilitate communication with infants and babies who yet cannot speak. Babies who were taught to use a simplified visual communication system can communicate their 48 Acoustics Today • Summer 2022