We then discuss recent approaches to studying how songbirds can coordinate their vocalization in reference to an external beat. We start with a brief review of rhythm learning assessment in human subjects, and present the difficulties in using comparable approaches in animal studies of rhythm learning. Here we review emerging evidence from studies of rhythm generation and vocal coordination across songbirds and humans.
In the case of rhythm learning, the experimental question is whether the animal is capable of anticipating the timing of events, which may be either equally spaced in time (i.e., isochrounous events, Figure 1C, top) or complex(i.e., hierarchically organized events corresponding to a musical meter, Figure 1C, bottom). In the case of sequences, one may ask if the animal has learned and responded to a simple or a complex string of contiguous events (Figure 1B). Alternatively animals might respond to sequences of events (Figure 1B) or to temporal pattens (Figure 1C), that is, to the overall periodicity of events. Such rhythms might simply arrise from stereotyped back and forth responses to individual stimuli (Figure 1A). Many animals communicate by exchanging rhythmic calls. What is it that makes entrainment so easy for a few animal species ( Large and Gray, 2015 Wilson and Cook, 2016) including humans, and difficult or impossible for others? Although rhythms, entrainment, and coordination appear to be widespread, some highly intelligent animals, such as dogs and apes, appear limited in their ability to spontaneously synchronize their actions to a given beat ( Merker, 2000 Fitch, 2011), whereas most humans can dance and can synchronize their movements to a broad range of beats with ease. Animals do not only adapt to rhythms, but they can also generate coordinated rhythmic patterns, as in the synchronous flashing of fireflies or the antiphonal calling of marmosets ( Moiseff and Copeland, 1995 Takahashi et al., 2013). From the entrainment of a cricket's circadian cycles, to a sandpiper's repeated chasing and retreating from the waves on a shoreline, rhythms, and synchronization are ubiquitous in animal behavior ( Strogatz, 2003). Building upon previous evidence for spontaneous entrainment in human and non-human vocal learners, we propose a comparative framework for future studies aimed at identifying shared mechanism of rhythm production and perception across songbirds and humans.Īlmost all animals behave in reference to physical and biological rhythms. In songbirds, this is driven, at least in part, by the forebrain song system, which controls song timing and is essential for vocal learning. This capacity resembles, to some extent, human predictive motor response to an external beat.
Surprisingly, zebra finches can readily learn to anticipate the calls of a “vocal robot” partner and alter the timing of their answers to avoid jamming, even in reference to complex rhythmic patterns. In particular, recently developed experimental methods have revealed neural mechanisms underlying the temporal structure of song and have allowed us to test birds' abilities to predict the timing of rhythmic social signals. It is not known, however, if songbirds can perceive rhythms holistically nor if they are capable of spontaneous entrainment to complex rhythms, in a manner similar to humans. In several species, birds can even coordinate the timing of their vocalizations with other individuals in duets that are synchronized with millisecond-accuracy. Songbirds have the ability to acquire songs and calls of various rhythms through imitation. Humans and oscine songbirds share the rare capacity for vocal learning. 3Jerusalem Academy of Music and Dance, Jerusalem, Israel.2Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat-Gan, Israel.1Department of Psychology, Hunter College, City University of New York, New York, NY, USA.Benichov 1 *, Eitan Globerson 2,3 and Ofer Tchernichovski 1
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