The Biology of Auditory Stress

Background: Darwin (1871) originally proposed the possibility that the evolutionary origins of music and language were shared. Both language and music occur in all human cultures, are primarily auditory but have closely related non-auditory components (e.g., sign/body language, dance). They can also both be analyzed in terms of phonology (sound system) and syntax (rules governing structure; see Fitch 2005; Masataka 2009; Patel & Daniele 2003 for reviews). Through comparing the behavioral capabilities of human and non-human animals, researchers can tease apart what aspects of language and music are uniquely human, and what aspects we share with other species in order to address their evolutionary origins (Hauser Chomsky & Fitch 2002; Fitch 2005). Goal: To date, phonology has received less attention than syntax in nonhuman animals despite its fundamentality in language (Yip 2006). One critical aspect of phonology is lexical stress, which helps a listener segment speech and distinguishes the meaning of words and sentences. Although there are differences in stress patterns across languages, there are also important universally perceived patterns suggesting that linguistic stress patterns are rooted in the biology of auditory communication (Hayes 1995; Cutler 2012). In music, the importance of stress is even more evident, with specific patterns of strong and weak components underlying rhythms popular all over the world. Here the goal is to systematically evaluate whether these stress patterns in language and music are domain-specific, and also whether they are a human-specific adaptation. Methods: The budgerigar (Melopsittacus undulatus) shares both the ability of vocal mimicry (being able to reproduce sounds experienced in their environment; Gramza 1970) and of rhythmic entrainment (being able to synchronize with a beat; Hasegawa et al., 2011) with humans and thus is an ideal candidate for cross-species analyses of stress perception. In contrast, the pigeon (Columba livia) and marmoset (Callithrix jacchus) do not have these capacities, but share closer phylogenetic histories with budgerigars and humans respectively. Accordingly, these four species will be trained to discriminate trochaic (stressed-unstressed) from iambic (unstressed-stressed) nonsense words (study 1), tones (study 2), or analogous visual stimuli (study 3) and then tested using a go/nogo operant conditioning paradigm (with which I have had much success in related work e.g., Hoeschele et al. 2011; 2012a; 2012b; 2013). Contribution: Auditory stress is a fundamental component of human language and music. These studies will determine: (1) whether the perception auditory stress is specific to the domain of language or music; and (2) whether the perception of auditory stress is uniquely human or shared with other species. The answers to these questions are relevant to ongoing work in cognitive science addressing linguistic and musical perception as well as animal behavior research aimed at understanding the evolution of what makes us human.

Did language and music evolve together? Charles Darwin thought they might have. Language and music share a lot of commonalities such as that they are both primarily auditory, but have closely-related non-auditory components (e.g., sign/body language, dance). They are processed by similar regions of the brain, both have structural rules, known as syntax, and both derive meaning from the way the sounds are produced, known as their phonology. Recently, researchers have been comparing humans to other species to see whether other animals that share aspects of our language capabilities also share our aspects of our musical capabilities and vice versa. In this way, we can begin to understand the evolution of these important aspects of what it means to be human. Although a lot of research comparing humans and other animals has focused on syntax, prior to this study little work had focused on phonology. One critical aspect of phonology is acoustic stress. Acoustic stress is the emphasis patterns found in both language and music. In language, perception of acoustic stress is important because it helps a listener segment speech and distinguishes the meaning of words and sentences. Although there are differences in stress patterns across languages, there are also important universally perceived patterns suggesting that linguistic stress patterns are rooted in the biology of auditory communication. In music, the importance of acoustic stress is even more evident, with specific patterns of strong and weak components underlying rhythms popular all over the world. By training several species to distinguish acoustic stress patterns, we found that humans are not the only species that attends to these patterns. We showed that both the budgerigar, a common small parrot often kept as a pet, and the rat were also able to detect acoustic stress patterns. However, the budgerigar species was much more flexible at detecting patterns than the rat. Not only that, by using a place preference paradigm we showed that female budgerigars preferred listening to rhythmic patterns rather than arrhythmic patterns, much like humans. These similar results between humans and budgerigars might be due to the fact that budgerigars communicate with complex learned vocalizations, can vocally imitate sounds in their environment, and detect and move to a beat in music, much like humans do when dancing. The results of this project support the idea that the abilities underlying language and music are not unique to humans and that other animals that produce complex language-like abilities also share music-like abilities with us such as the preference for rhythmic sounds.