Social influences on song learning
Introduction
In most animal species, only a fraction of juveniles survive to maturity. Young social animals, in addition to being small, inexperienced, and vulnerable, must also learn how to successfully integrate within their group. They must learn how to identify and interact with friends and enemies [1, 2], and how to utilize public and private space [3]. In vocal learners such as songbirds and humans, juveniles must also learn complex vocal communication skills, which are often initially shaped by social interactions with parents. Later, social learning continues not only through direct (potentially agonistic) interactions with peers but also by attending to the consequences of interactions between others (Figure 1). The complexity of these factors, and the long duration of vocal development, make it difficult to assess how social forces combine to shape the outcomes of vocal development [4].
In humans, even two-day-old infants prefer to listen to infant-directed speech [5], which is higher in pitch, simplified in grammar, and slower overall [6]. These adjustments facilitate word recognition [7] and segmentation [8] by infants. The timing of vocal exchanges with the caregiver is particularly important: nine-month-old infants can quickly match the phonological structure of their mother's vocalizations, but only if she answers their babbling promptly [9]. Similar influences have been observed in songbirds: juvenile zebra finches produce poor imitation of non-interactive song playbacks, but copy live tutors with high accuracy [10, 11]. Vocal development in songbirds is also susceptible to complex social interactions with peers and adults other than parents [12, 13]. There is a large diversity of song learning strategies across songbird species, including differences in the timing and speed of learning, repertoire size, and the degree of imitation [14]. Here we focus on songbirds that are age-limited learners, where social influences occur within a narrow developmental window [14, 15], making it feasible to track an entire vocal development under controlled conditions [16, 17]. We review recent technical advances for quantifying the cumulative influences of social factors on vocal development. We start with techniques for tracking vocal interactions, non-vocal communication, and eavesdropping. We then present a framework for a more ambitious approach of experimenting with virtual social environments (VSE), in order to test the influence of specific social variables and potential synergies between them. If successful, VSEs could test a broad range of hypotheses about how songbirds interpret and incorporate social information during vocal development.
Section snippets
Social influences on vocal development
Song learning is inherently social, but the social environment can shape the course of vocal development at different levels:
Tracking social interactions during song development
Song learning is a means by which an individual establishes its place within a social network. Recent advances in computation power, data storage, and miniaturization of electronic devices have made it possible to study song development continuously [36, 37] and even across generations [38], but only in laboratory environments where social interactions are either restricted, or nonexistent. Field studies provide ecological validity, but monitoring vocal development in the wild is usually not
Toward virtual social environments (VSEs) for studying vocal development
Continuous monitoring of social interactions is likely to provide deeper understanding of song development. However, establishing causality from such complex longitudinal data is unlikely to succeed unless complemented by controlled studies. We suggest that this can be achieved by developing VSEs that simulate the social context of song learning, through iterative interactions between the developing bird and a computerized visual and vocal interface. Video playbacks have been successfully used
Conclusions
Birdsong, like human language, is culturally transmitted and figuring out how social processes accumulate to shape vocal learning in songbirds is now within reach. In this review we highlighted three categories of social factors that are likely to play a role in vocal development in both humans and songbirds: vocal interactions, non-vocal communication, and eavesdropping as means of acquiring information about the social world. Designing VSEs to test specific hypotheses about social influences
Conflict of interest
None declared.
Acknowledgments
We thank Petra Ljubičić and Kirsten Canfield for the use of their artwork. Supported by NSF grant 1261872 to OT.
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