But there is no evidence that such vocalizations are learned or that are composed by an organization of categorically different segments as are the vocalizations produced by songbirds and humans. Importantly, rats can discriminate when the fundamental frequency and duration of these vocalizations change (Brudzynski 2014 Simola and Brudzynski 2018). Rats produce two types of ultrasonic vocalizations, aversive (at 22 kHz) and appetitive (at 50 kHz), by releasing air through the vocal tract (Brudzynski 2014). In the present study, we use the rat ( Rattus Norvegicus) as a model to explore the detection of changes in pitch, tempo and timbre in a tune. It is thus important to understand the extent to which this ability is based on sensitivities already present in other species. However, a key aspect in how humans process music is that we perceive musical structures in a relative instead of in an absolute way that is, independently of surface changes along features such as pitch, tempo and timbre. chimpanzees black-capped chickadees zebra finches ). California sea lion cockatoo ) and spectral envelope (i.e. For instance, both mammalian and avian species can perceive changes in fundamental frequency (i.e. Other studies identified more specific musical features that can be detected by other animals. However, since the contrasting excerpts varied along several dimensions, it is difficult to identify the specific features that the animals were using as a cue to guide their discrimination. Bach versus Stravinsky, or blues versus classical music). For instance, pigeons (Porter and Neuringer 1984), rats (Okaichi and Okaichi 2001) and even carps (Chase 2001) have been shown to discriminate excerpts of songs drawn from different musical traditions (e.g. Some earlier studies explored whether different animals can discriminate among musical styles using a variety of cues. One way to address this issue has been by exploring the extent to which these features might arise from sensitivities that are already present in other animals (Fitch 2006 Hoeschele et al. reliance on simple frequency ratios, or variations along rhythmic and harmonic complexity) emerge from specific perceptual and cognitive constraints that predate the emergence of music. For example, there are open questions about whether certain common features present in music (e.g. The universality of key components in music has attracted much attention in recent years (Mehr et al. But to what extent does humans’ biological predisposition to process music emerge from sensitivities already present in non-human animals? In the present study we explore whether a distant non-vocal learner species, the rat ( Rattus norvegicus), detects surface changes in a familiar tune. In fact, this melody recognition ability is so pervasive in humans that is already present in infants as young as two-month olds (Plantinga and Trainor 2009), and is one of the building blocks upon which music appreciation is based. pitch, tempo and timbre) without losing its identity. This is because we identify a musical excerpt as an object that can flexibly vary in at least these three dimensions (i.e. Despite that, all the members of the party will identify the song, even those who know the lyrics in a different language. For instance, at every birthday party, the happy birthday song is sung by different people (with varying individual voices) at distinct frequency ranges and at a randomly-chosen speed (at a slower or faster tempo depending on the enthusiasm and general mood). Much like we can understand a given sentence independently of the gender or accent of the speaker, and even if it is shouted or whispered, the recognition of a familiar tune is done effortlessly regardless of the specific instrument it is used to play it or the speed and octave at which it is played. While the rats responded differently to the familiar and the novel version of the tune when it was played on novel instruments, they did not respond differently to the original song and its novel versions that included octave transpositions and changes in tempo. We then presented novel test items that included changes in pitch (higher and lower octave transpositions), tempo (double and half the speed) and timbre (violin and piccolo). We familiarized the animals (Long–Evans rats) with the “Happy Birthday” tune on a piano. Here we explore whether other animals react to surface changes in a tune. Despite the uniqueness of our music faculty, there is the possibility that key aspects in music processing emerge from general sensitivities already present in other species. Much of the way in which we engage with music relies in our ability to normalize across these surface changes. Humans recognize a melody independently of whether it is played on a piano or a violin, faster or slower, or at higher or lower frequencies.
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