Iterative learning experiments can help elucidate music's origins.

Anglada-Tort et al. Current Biology, 33, 1472-1486.e12, (2023) conducted a large-scale iterative learning study with cross-cultural human participants to understand how musical structure emerges. Together with archaeological, developmental, historical cross-cultural music data, and cross-species studies we can begin to elucidate the origins of music.

A comparison between common marmosets (Callithrix jacchus) and human infants sheds light on traits proposed to be at the root of human octave equivalence.

Two notes separated by a doubling in frequency sound similar to humans. This "octave equivalence" is critical to perception and production of music and speech and occurs early in human development. Because it also occurs cross-culturally, a biological basis of octave equivalence has been hypothesized. Members of our team previousy suggested four human traits are at the root of this phenomenon: (1) vocal learning, (2) clear octave information in vocal harmonics, (3) differing vocal ranges, and (4) vocalizing together. Using cross-species studies, we can test how relevant these respective traits are, while controlling for enculturation effects and addressing questions of phylogeny. Common marmosets possess forms of three of the four traits, lacking differing vocal ranges. We tested 11 common marmosets by adapting an established head-turning paradigm, creating a parallel test to an important infant study. Unlike human infants, marmosets responded similarly to tones shifted by an octave or other intervals. Because previous studies with the same head-turning paradigm produced differential results to discernable acoustic stimuli in common marmosets, our results suggest that marmosets do not perceive octave equivalence. Our work suggests differing vocal ranges between adults and children and men and women and the way they are used in singing together may be critical to the development of octave equivalence. RESEARCH HIGHLIGHTS: A direct comparison of octave equivalence tests with common marmosets and human infants Marmosets show no octave equivalence Results emphasize the importance of differing vocal ranges between adults and infants.

Black-capped chickadees (Poecile atricapillus) discriminate between naturally-ordered and scramble-ordered chick-a-dee calls and individual preference is related to rate of learning.

Though many forms of animal communication are not reliant on the order in which components of signals are combined to be effective, there is evidence that order does matter for some communication systems. In the light of differential responding to calls of varying note-order observed in black-capped chickadees in the field, we set out to determine whether chickadees recognize syntactically-ordered and incorrectly-ordered chick-a-dee calls as separate and distinct conceptual categories using both an auditory preference task and go/no-go operant conditioning paradigm. Results show that chickadees spent more time on the perch that did not produce sound (i.e., silent perch) than on either of the acoustic perches (i.e., natural and scrambled order chick-a-dee call playback) and visited the perch associated with naturally-ordered calls more often than the perch associated with scrambled-order calls. Birds in both the True natural- and scrambled-order call groups continued to respond according to the contingencies that they learned in Discrimination training, indicating that black-capped chickadees are capable of perceiving and acting upon the categories of natural- versus scrambled-ordered calls.

Lessons learned in animal acoustic cognition through comparisons with humans.

Humans are an interesting subject of study in comparative cognition. While humans have a lot of anecdotal and subjective knowledge about their own minds and behaviors, researchers tend not to study humans the way they study other species. Instead, comparisons between humans and other animals tend to be based on either assumptions about human behavior and cognition, or very different testing methods. Here we emphasize the importance of using insider knowledge about humans to form interesting research questions about animal cognition while simultaneously stepping back and treating humans like just another species as if one were an alien researcher. This perspective is extremely helpful to identify what aspects of cognitive processes may be interesting and relevant across the animal kingdom. Here we outline some examples of how this objective human-centric approach has helped us to move forward knowledge in several areas of animal acoustic cognition (rhythm, harmonicity, and vocal units). We describe how this approach works, what kind of benefits we obtain, and how it can be applied to other areas of animal cognition. While an objective human-centric approach is not useful when studying traits that do not occur in humans (e.g., magnetic spatial navigation), it can be extremely helpful when studying traits that are relevant to humans (e.g., communication). Overall, we hope to entice more people working in animal cognition to use a similar approach to maximize the benefits of being part of the animal kingdom while maintaining a detached and scientific perspective on the human species.

Pitch chroma information is processed in addition to pitch height information with more than two pitch-range categories.

Octave equivalence describes the perception that notes separated by a doubling in frequency sound similar. While the octave is used cross-culturally as a basis of pitch perception, experimental demonstration of the phenomenon has proved to be difficult. In past work, members of our group developed a three-range generalization paradigm that reliably demonstrated octave equivalence. In this study we replicate and expand on this previous work trying to answer three questions that help us understand the origins and potential cross-cultural significance of octave equivalence: (1) whether training with three ranges is strictly necessary or whether an easier-to-learn two-range task would be sufficient, (2) whether the task could demonstrate octave equivalence beyond neighbouring octaves, and (3) whether language skills and musical education impact the use of octave equivalence in this task. We conducted a large-sample study using variations of the original paradigm to answer these questions. Results found here suggest that the three-range discrimination task is indeed vital to demonstrating octave equivalence. In a two-range task, pitch height appears to be dominant over octave equivalence. Octave equivalence has an effect only when pitch height alone is not sufficient. Results also suggest that effects of octave equivalence are strongest between neighbouring octaves, and that tonal language and musical training have a positive effect on learning of discriminations but not on perception of octave equivalence during testing. We discuss these results considering their relevance to future research and to ongoing debates about the basis of octave equivalence perception.

Cultural evolution: Conserved patterns of melodic evolution across musical cultures.

A new study finds that melodies evolve in similar ways, reminiscent of genetic evolution, across cultures. Patterns of change in music and other aesthetic domains may be the key to understanding how culture evolves when unfettered by physical or ecological constraints.

Progress without exclusion in the search for an evolutionary basis of music.

Mehr et al.'s hypothesis that the origins of music lie in credible signaling emerges here as a strong contender to explain early adaptive functions of music. Its integration with evolutionary biology and its specificity mark important contributions. However, much of the paper is dedicated to the exclusion of popular alternative hypotheses, which we argue is unjustified and premature.

Universal principles underlying segmental structures in parrot song and human speech.

Despite the diversity of human languages, certain linguistic patterns are remarkably consistent across human populations. While syntactic universals receive more attention, there is stronger evidence for universal patterns in the inventory and organization of segments: units that are separated by rapid acoustic transitions which are used to build syllables, words, and phrases. Crucially, if an alien researcher investigated spoken human language how we analyze non-human communication systems, many of the phonological regularities would be overlooked, as the majority of analyses in non-humans treat breath groups, or "syllables" (units divided by silent inhalations), as the smallest unit. Here, we introduce a novel segment-based analysis that reveals patterns in the acoustic output of budgerigars, a vocal learning parrot species, that match universal phonological patterns well-documented in humans. We show that song in four independent budgerigar populations is comprised of consonant- and vowel-like segments. Furthermore, the organization of segments within syllables is not random. As in spoken human language, segments at the start of a vocalization are more likely to be consonant-like and segments at the end are more likely to be longer, quieter, and lower in fundamental frequency. These results provide a new foundation for empirical investigation of language-like abilities in other species.

Is consonance attractive to budgerigars? No evidence from a place preference study.

Consonant tone combinations occur naturally in the overtone series of harmonic sounds. These include sounds that many non-human animals produce to communicate. As such, non-human animals may be attracted to consonant intervals, interpreting them, e.g., as a feature of important social stimuli. There is preliminary evidence of attraction to consonance in various bird species in the wild, but few experimental studies with birds. We tested budgerigars (Melopsittacus undulatus) for attraction to consonant over dissonant intervals in two experiments. In Experiment 1, we tested humans and budgerigars using a place preference paradigm in which individuals could explore an environment with multiple sound sources. Both species were tested with consonant and dissonant versions of a previously studied piano melody, and we recorded time spent with each stimulus as a measure of attraction. Human females spent more time with consonant than dissonant stimuli in this experiment, but human males spent equal time with both consonant and dissonant stimuli. Neither male nor female budgerigars spent more time with either stimulus type. In Experiment 2, we tested budgerigars with more ecologically relevant stimuli comprised of sampled budgerigar vocalizations arranged into consonant or dissonant chords. These stimuli, however, also failed to produce any evidence of preference in budgerigar responses. We discuss these results in the context of ongoing research on the study of consonance as a potential general feature of auditory perception in animals with harmonic vocalizations, with respect to similarities and differences between human and budgerigar vocal behaviour, and future methodological directions.

Novel methodology to assess vocal learning in nature.

A recent and thorough longitudinal study by Mennill and colleagues (Current Biology, 28(20), 3273-3278, 2018) provides the first direct evidence for vocal learning in wild birds. Reconciling these findings with prior laboratory evidence and indirect evidence for vocal learning in the field provides novel insight into the vocal learning process in songbirds.

Temporal modulation in speech, music, and animal vocal communication: evidence of conserved function.

Speech is a distinctive feature of our species. It is the default channel for language and constitutes our primary mode of social communication. Determining the evolutionary origins of speech is a challenging prospect, in large part because it appears to be unique in the animal kingdom. However, direct comparisons between speech and other forms of acoustic communication, both in humans (music) and animals (vocalization), suggest that important components of speech are shared across domains and species. In this review, we focus on a single aspect of speech-temporal patterning-examining similarities and differences across speech, music, and animal vocalization. Additional structure is provided by focusing on three specific functions of temporal patterning across domains: (1) emotional expression, (2) social interaction, and (3) unit identification. We hypothesize an evolutionary trajectory wherein the ability to identify units within a continuous stream of vocal sounds derives from social vocal interaction, which, in turn, derives from vocal emotional communication. This hypothesis implies that unit identification has parallels in music and precursors in animal vocal communication. Accordingly, we demonstrate the potential of comparisons between fundamental domains of biological acoustic communication to provide insight into the evolution of language.

Common marmosets are sensitive to simple dependencies at variable distances in an artificial grammar.

Recognizing that two elements within a sequence of variable length depend on each other is a key ability in understanding the structure of language and music. Perception of such interdependencies has previously been documented in chimpanzees in the visual domain and in human infants and common squirrel monkeys with auditory playback experiments, but it remains unclear whether it typifies primates in general. Here, we investigated the ability of common marmosets (Callithrix jacchus) to recognize and respond to such dependencies. We tested subjects in a familiarization-discrimination playback experiment using stimuli composed of pure tones that either conformed or did not conform to a grammatical rule. After familiarization to sequences with dependencies, marmosets spontaneously discriminated between sequences containing and lacking dependencies ('consistent' and 'inconsistent', respectively), independent of stimulus length. Marmosets looked more often to the sound source when hearing sequences consistent with the familiarization stimuli, as previously found in human infants. Crucially, looks were coded automatically by computer software, avoiding human bias. Our results support the hypothesis that the ability to perceive dependencies at variable distances was already present in the common ancestor of all anthropoid primates (Simiiformes).

A technological framework for running and analyzing animal head turning experiments.

Head turning experiments are widely used to test the cognition of both human infants and non-human animal species. Monitoring head turns allows researchers to non-invasively assess attention to acoustic or visual stimuli. In the majority of head turning experiments, the head direction analyses have been accomplished manually, which is extremely labor intensive and can be affected by subjectivity or other human errors and limitations. In the current study, we introduce an open-source computer program for measuring head directions of freely moving animals including common marmoset monkeys (Callithrix jacchus), American alligators (Alligator mississippiensis), and Mongolian gerbils (Meriones unguiculatus) to reduce human effort and time in video coding. We also illustrate an exemplary framework for an animal head turning experiment with common marmoset monkeys. This framework incorporates computer-aided processes of data acquisition, preprocessing, and analysis using the aforementioned software and additional open-source software and hardware.

Humans recognize emotional arousal in vocalizations across all classes of terrestrial vertebrates: evidence for acoustic universals.

Writing over a century ago, Darwin hypothesized that vocal expression of emotion dates back to our earliest terrestrial ancestors. If this hypothesis is true, we should expect to find cross-species acoustic universals in emotional vocalizations. Studies suggest that acoustic attributes of aroused vocalizations are shared across many mammalian species, and that humans can use these attributes to infer emotional content. But do these acoustic attributes extend to non-mammalian vertebrates? In this study, we asked human participants to judge the emotional content of vocalizations of nine vertebrate species representing three different biological classes-Amphibia, Reptilia (non-aves and aves) and Mammalia. We found that humans are able to identify higher levels of arousal in vocalizations across all species. This result was consistent across different language groups (English, German and Mandarin native speakers), suggesting that this ability is biologically rooted in humans. Our findings indicate that humans use multiple acoustic parameters to infer relative arousal in vocalizations for each species, but mainly rely on fundamental frequency and spectral centre of gravity to identify higher arousal vocalizations across species. These results suggest that fundamental mechanisms of vocal emotional expression are shared among vertebrates and could represent a homologous signalling system.

Animal Pitch Perception: Melodies and Harmonies.

Pitch is a percept of sound that is based in part on fundamental frequency. Although pitch can be defined in a way that is clearly separable from other aspects of musical sounds, such as timbre, the perception of pitch is not a simple topic. Despite this, studying pitch separately from other aspects of sound has led to some interesting conclusions about how humans and other animals process acoustic signals. It turns out that pitch perception in humans is based on an assessment of pitch height, pitch chroma, relative pitch, and grouping principles. How pitch is broken down depends largely on the context. Most, if not all, of these principles appear to also be used by other species, but when and how accurately they are used varies across species and context. Studying how other animals compare to humans in their pitch abilities is partially a reevaluation of what we know about humans by considering ourselves in a biological context.

Generalizing prosodic patterns by a non-vocal learning mammal.

Prosody, a salient aspect of speech that includes rhythm and intonation, has been shown to help infants acquire some aspects of syntax. Recent studies have shown that birds of two vocal learning species are able to categorize human speech stimuli based on prosody. In the current study, we found that the non-vocal learning rat could also discriminate human speech stimuli based on prosody. Not only that, but rats were able to generalize to novel stimuli they had not been trained with, which suggests that they had not simply memorized the properties of individual stimuli, but learned a prosodic rule. When tested with stimuli with either one or three out of the four prosodic cues removed, the rats did poorly, suggesting that all cues were necessary for the rats to solve the task. This result is in contrast to results with humans and budgerigars, both of which had previously been studied using the same paradigm. Humans and budgerigars both learned the task and generalized to novel items, but were also able to solve the task with some of the cues removed. In conclusion, rats appear to have some of the perceptual abilities necessary to generalize prosodic patterns, in a similar though not identical way to the vocal learning species that have been studied.

Sex Differences in Rhythmic Preferences in the Budgerigar (Melopsittacus undulatus): A Comparative Study with Humans.

A variety of parrot species have recently gained attention as members of a small group of non-human animals that are capable of coordinating their movements in time with a rhythmic pulse. This capacity is highly developed in humans, who display unparalleled sensitivity to musical beats and appear to prefer rhythmically organized sounds in their music. Do parrots also exhibit a preference for rhythmic over arrhythmic sounds? Here, we presented humans and budgerigars (Melopsittacus undulatus) - a small parrot species that have been shown to be able to align movements with a beat - with rhythmic and arrhythmic sound patterns in an acoustic place preference paradigm. Both species were allowed to explore an environment for 5 min. We quantified how much time they spent in proximity to rhythmic vs. arrhythmic stimuli. The results show that humans spent more time with rhythmic stimuli, and also preferred rhythmic stimuli when directly asked in a post-test survey. Budgerigars did not show any such overall preferences. However, further examination of the budgerigar results showed an effect of sex, such that male budgerigars spent more time with arrthymic stimuli, and female budgerigars spent more time with rhythmic stimuli. Our results support the idea that rhythmic information is interesting to budgerigars. We suggest that future investigations into the temporal characteristics of naturalistic social behaviors in budgerigars, such as courtship vocalizations and head-bobbing displays, may help explain the sex difference we observed.

Phonological perception by birds: budgerigars can perceive lexical stress.

Metrical phonology is the perceptual "strength" in language of some syllables relative to others. The ability to perceive lexical stress is important, as it can help a listener segment speech and distinguish the meaning of words and sentences. Despite this importance, there has been little comparative work on the perception of lexical stress across species. We used a go/no-go operant paradigm to train human participants and budgerigars (Melopsittacus undulatus) to distinguish trochaic (stress-initial) from iambic (stress-final) two-syllable nonsense words. Once participants learned the task, we presented both novel nonsense words, and familiar nonsense words that had certain cues removed (e.g., pitch, duration, loudness, or vowel quality) to determine which cues were most important in stress perception. Members of both species learned the task and were then able to generalize to novel exemplars, showing categorical learning rather than rote memorization. Tests using reduced stimuli showed that humans could identify stress patterns with amplitude and pitch alone, but not with only duration or vowel quality. Budgerigars required more than one cue to be present and had trouble if vowel quality or amplitude were missing as cues. The results suggest that stress patterns in human speech can be decoded by other species. Further comparative stress-perception research with more species could help to determine what species characteristics predict this ability. In addition, tests with a variety of stimuli could help to determine how much this ability depends on general pattern learning processes versus vocalization-specific cues.

Searching for the origins of musicality across species.

In the introduction to this theme issue, Honing et al. suggest that the origins of musicality--the capacity that makes it possible for us to perceive, appreciate and produce music--can be pursued productively by searching for components of musicality in other species. Recent studies have highlighted that the behavioural relevance of stimuli to animals and the relation of experimental procedures to their natural behaviour can have a large impact on the type of results that can be obtained for a given species. Through reviewing laboratory findings on animal auditory perception and behaviour, as well as relevant findings on natural behaviour, we provide evidence that both traditional laboratory studies and studies relating to natural behaviour are needed to answer the problem of musicality. Traditional laboratory studies use synthetic stimuli that provide more control than more naturalistic studies, and are in many ways suitable to test the perceptual abilities of animals. However, naturalistic studies are essential to inform us as to what might constitute relevant stimuli and parameters to test with laboratory studies, or why we may or may not expect certain stimulus manipulations to be relevant. These two approaches are both vital in the comparative study of musicality.