The Vocal Imitation is a software module that allows the user to imitate vocal characters segments from one person into other person voice in such a way that a second person voice shall be heard speaking in the same voice as the first person.
Vocal Imitation V5 | tested
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We tested the ability of a beluga (Delphinapterus leucas) to imitate sounds presented to it. During the training session, we presented the subject three recorded sounds that were emitted by the subject, and the subject was trained to imitate them. The subject learned to correctly imitate the sounds. During the test session, two novel computer-generated artificial sounds were presented through an audio speaker. In addition, nine arbitrary vocal sounds produced by the experimenter were presented to the subject, and the subject was required to imitate them. Seven persons, who were not involved in the experiment, were presented the sample sounds and imitated calls; subsequently, they judged whether both sounds were similar to each other. In addition, sound spectrums of the sample sounds and imitated calls were analyzed. As a result, some components of the sound spectrums were similar, and most of imitated calls possess spectral features similar to the sample sounds. These results demonstrated that the beluga was able to correctly imitate novel sounds and spontaneously displayed aptitude for imitation.
Vocal learning is the ability to modify acoustic and syntactic sounds, acquire new sounds via imitation, and produce vocalizations. "Vocalizations" in this case refers only to sounds generated by the vocal organ (mammalian larynx or avian syrinx) as opposed to by the lips, teeth, and tongue, which require substantially less motor control.[1] A rare trait, vocal learning is a critical substrate for spoken language and has only been detected in eight animal groups despite the wide array of vocalizing species; these include humans, bats, cetaceans, pinnipeds (seals and sea lions), elephants, and three distantly related bird groups including songbirds, parrots, and hummingbirds. Vocal learning is distinct from auditory learning, or the ability to form memories of sounds heard, a relatively common trait which is present in all vertebrates tested. For example, dogs can be trained to understand the word "sit" even though the human word is not in its innate auditory repertoire (auditory learning). However, the dog cannot imitate and produce the word "sit" itself as vocal learners can.
Historically, species have been classified into the binary categories of vocal learner or vocal non-learner based on their ability to produce novel vocalizations or imitate other species, with evidence from social isolation, deafening studies, and cross-fostering experiments.[1] However, vocal learners exhibit a great deal of plasticity or variation between species, resulting in a spectrum of ability. The vocalizations of songbirds and whales have a syntactic-like organization similar to that of humans but are limited to Finite-State Grammars (FSGs), where they can generate strings of sequences with limited structural complexity.[2] Humans, on the other hand, show deeper hierarchical relationships, such as the nesting of phrases within others, and demonstrate compositional syntax, where changes in syntactic organization generate new meanings, both of which are beyond the capabilities of other vocal learning groups[3]
Vocal learning phenotype also differ within groups and closely related species will not display the same abilities. Within avian vocal learners, for example, zebra finch songs only contain strictly linear transitions that go through different syllables in a motif from beginning to end, yet mockingbird and nightingale songs show element repetition within a range of legal repetitions, non-adjacent relationships between distant song elements, and forward and backward branching in song element transitions.[4] Parrots are even more complex as they can imitate the speech of heterospecifics like humans and synchronize their movements to a rhythmic beat.[5]
The most extensively studied model organisms of vocal learning are found in birds, namely songbirds, parrots, and hummingbirds. The degree of vocal learning in each specific species varies. While many parrots and certain songbirds like canaries can imitate and spontaneously combine learned sounds during all periods of their life, other songbirds and hummingbirds are limited to a certain songs learned during their critical period.
The first evidence for audio-vocal learning in a non-human mammal was produced by Karl-Heinz Esser in 1994. Hand-reared infant lesser spear-nosed bats (Phyllostomos discolor) were able to adapt their isolation calls to an external reference signal. Isolation calls in a control group that had no reference signal did not show the same adaptation.[8]
Further evidence for vocal learning in bats appeared in 1998 when Janette Wenrick Boughman studied female greater spear-nosed bats (Phyllostomus hastatus). These bats live in unrelated groups and use group contact calls that differ among social groups. Each social group has a single call, which differs in frequency and temporal characteristics. When individual bats were introduced to a new social group, the group call began to morph, taking on new frequency and temporal characteristics, and over time, calls of transfer and resident bats in the same group more closely resembled their new modified call than their old calls.[9]
Male humpback whales (Megaptera novaeangliae) sing as a form of sexual display while migrating to and from their breeding grounds. All males in a population produce the same song which can change over time, indicating vocal learning and cultural transmission, a characteristic shared by some bird populations. Songs become increasingly dissimilar over distance and populations in different oceans have dissimilar songs.
Captive bottlenose dolphins (Tursiops truncatus) can be trained to emit sounds through their blowhole in open air. Through training, these vocal emissions can be altered from natural patterns to resemble sounds like the human voice, measurable through the number of bursts of sound emitted by the dolphin. In 92% of exchanges between humans and dolphins, the number of bursts equaled 1 of the number of syllables spoken by a human.[12] Another study used an underwater keyboard to demonstrate that dolphins are able to learn various whistles in order to do an activity or obtain an object. Complete mimicry occurred within ten attempts for these trained dolphins.[13] Other studies of dolphins have given even more evidence of spontaneous mimicry of species-specific whistles and other biological and computer-generated signals.[14]
Such vocal learning has also been identified in wild bottlenose dolphins. Bottlenose dolphins develop a distinct signature whistle in the first few months of life, which is used to identify and distinguish itself from other individuals. This individual distinctiveness could have been a driving force for evolution by providing higher species fitness since complex communication is largely correlated with increased intelligence. However, vocal identification is present in vocal non-learners as well. Therefore, it is unlikely that individual identification was a primary driving force for the evolution of vocal learning. Each signature whistle can be learned by other individuals for identification purposes and are used primarily when the dolphin in question is out of sight. Bottlenose dolphins use their learned whistles in matching interactions, which are likely to be used while addressing each other, signalling alliance membership to a third party, or preventing deception by an imitating dolphin.[15]
Mate attraction and territory defense have also been seen as possible contributors to vocal learning evolution. Studies on this topic point out that while both vocal learners and non-learners use vocalizations to attract mates or defend territories, there is one key difference: variability. Vocal learners can produce a more varied arrangement of vocalizations and frequencies, which studies show may be more preferred by females. For example, Caldwell[16] observed that male Atlantic bottlenose dolphins may initiate a challenge by facing another dolphin, opening its mouth, thereby exposing its teeth, or arching its back slightly and holding its head downward. This behavior is more along the lines of visual communication but still may or may not be accompanied by vocalizations such as burst-pulsed sounds. The burst-pulsed sounds, which are more complex and varied than the whistles, are often utilized to convey excitement, dominance or aggression such as when they are competing for the same piece of food.[17] The dolphins also produce these forceful sounds when in the presence of other individuals moving towards the same prey. On the sexual side, Caldwell saw that dolphins may solicit a sexual response from another by swimming in front of it, looking back, and rolling on its side to display the genital region.[18] These observations provide yet another example of visual communication where dolphins exhibit different postures and non-vocal behaviors to communicate with others that also may or may not be accompanied by vocalizations. Sexual selection for greater variability, and thus in turn vocal learning, may then be a major driving force for the evolution of vocal learning. 2ff7e9595c
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