Page 47 - Summer2022

can see the tuning of those instruments across a piano range. Those instruments have different physical proper- ties, from the resonant body, through the length of the neck, to the thickness of the strings. All of them have four strings, but those strings are tuned very differently from one another. For example, we would not expect any of the strings of a large instrument, like a double bass, to be tuned to E5, which is usually the tuning of the highest string on the regular-sized violin. The larger the instru- ment, the lower it might sound and vice versa. The correspondence between sound and visual size might stem from such physical properties. The theory explain- ing this connection in humans and other animals is called the “frequency code” and was proposed by Ohala (1994). Among other examples, Ohala stated that lower frequen- cies typically originate from larger sources and higher frequencies from smaller sources. This drives our expec- tations and can, in turn, be mapped onto more abstract relationships that we can create with the tone of voice, such as the fundamental frequency. Thus, he says that a lower fundamental frequency expresses dominance and a higher fundamental frequency submissiveness. In the end, being larger in the animal kingdom might make an animal threatening and more attractive for mating. These basic correspondences can move into broader sociocultural uses. Using a high fundamental frequency with exaggerated peaks is typical for child-directed speech. And the reason for that might be that it seems less threatening and more playful to children. As an opposite example, we might look at the so-called “creaky voice,” as an extreme case of vocal fry (sounding like an aperiodic low voice; see youtu.be/4L7-9N1xQZA) caused by shortening the vocal folds and lowering the funda- mental frequency, occurring mostly in young women. It started gaining popularity in the 1960s and was later cov- ered in pop culture (see Frank and Moon Zappa’s song “Valley Girl,” at youtu.be/Qb21lsCQ3EM). Originally, the strategy of lowering the fundamental frequency should evoke the image of competence; however, the actual per- ception of this phenomenon is mixed. Therefore, we have to bear in mind that some abstract social meanings such ascompetenceorpolitenessseemmorecomplicatedand may interfere with the use of the frequency code (Winter et al., 2021). Nevertheless, we might still find support for it in our own voice use in different contexts. Cross-Modal Correspondence and Language Evolution Meaningful cross-modal correspondence between sound and size is not only something that humans perceive and use. It is a crucial mechanism in the animal kingdom and its relevance has at least the two following reasons. First, animals sense danger using a variety of perceptual signals, with hearing being a particularly powerful sense. Second, some animals use the sound-to-size corre- spondence as a deceptive strategy to their evolutionary advantage (e.g., Bee et al., 2000). A signal can be decep- tive if it does not correspond to the actual body size of the vocalizing animal but implies a bigger animal. In that case, it can be a potential threat to the receiver and may increase the chance of survival and mating success. To what extent such a signal is intentional or not is not the main concern of this paper. The use of voice for size esti- mation is perhaps best visible in the behavior of various deer species (e.g., Reby et al., 2005). The question here is about perception and adaptation. When confronted with roars that suggest a large-sized caller, male red deer respond more frequently and extend their vocal tract due to laryngeal lowering that changes their resonant fre- quencies (Reby et al., 2005). Studies also show that larger deer have lower frequencies and through that, indirectly, a higher mating success (Vannoni and McElligott, 2008). The use of sound to deceive and communicate an exagger- ated size has been shown in a variety of species so far (e.g., Bee et al., 2000). Some examples include squirrels, birds, and frogs. The deception can function across and within species. For example, juvenile squirrels imitate the voice of their par- ents to drive away predators (Matrosova et al., 2007). Birds may strategically use vocalizations of their predators to fool fellow birds and enjoy an uninterrupted feast on flies themselves (Munn, 1986). Some frog species lower their fundamental frequency to seem larger in the eyes of other frogs and protect their territory (Bee et al., 2000). Research on Primates: Empirical Research Is Mostly Unimodal Although discoveries about sound-sized linkages in animal communication promised to be very fruit- ful, most studies on primates have been unimodal. In the early stages of research in this field, many findings evolved around the gesture-first theory (Hewes, 1973). Summer 2022 • Acoustics Today 47