Hoover the talking seal

Abstract

Hoover, who? Hoover (1971–1985; Figure 1) was a male harbor seal (Phoca vitulina) famous for imitating human speech, who spent most of his life at the New England Aquarium in Boston, USA. Initially raised by a Maine fisherman, Hoover began imitating English phrases once he reached sexual maturity. The seal’s repertoire included “hello there”, “come over here”, “hurry”, “hey hey”, and “Hoover”. Hoover provides an unparalleled example of speech mimicry — a form of vocal learning — in seals. How did a seal learn to parrot human speech? Hoover was an orphaned seal, found at Bethel Point, Maine, in 1971 and rescued a few weeks after his birth. George Swallow took the orphaned pup home, handfeeding and frequently speaking to him. Growing fast, Hoover was donated to the New England Aquarium at about three months. He started producing speech-like sounds much later, around his fifth birthday. Hoover produced his speech-like vocalizations typically in the water, from a vertical position, followed by bubble blowing. These vocal displays were especially frequent during breeding season, and often appeared directed at female seals, suggesting that these vocalizations may have acted as ‘breeding songs’ like those produced by male harbor seals. Importantly, the aquarium staff did not train Hoover to produce these displays. Did Hoover faithfully copy speech, or simply trick us into thinking he does? One might think that Hoover was no different from some ‘YouTube stars’, like Siamese cats or Huskies that say ‘Mama’ or ‘I love you’. Human perception is so attuned to finding (speech) patterns that some animals may trick our brains into hearing speech sounds where no such similarity exists. However, in the case of Hoover there is solid evidence for speech mimicry: spectrograms of his sounds (tools to visualize and compare animal or human voices) show that Hoover’s vocalizations were indeed very ‘human-like’, containing the typical formant modulations that we use to produce vowels and consonants. Ongoing quantitative and statistical analyses of Hoover’s vowel sounds also suggest that indeed this seal produced human-like English vowels. Thus, Hoover is one of the best-documented examples of vocal production learning of human speech available in a mammal. What is vocal production learning? Vocal production learning is a form of social learning. Rare among mammals, it is the ability to produce new sounds or alter existing ones based on experience with others, such as humans learning new languages, or parrots mimicking speech. Vocal production learning and mimicry require mapping perceived sounds to movements of the vocal production system and rely on specialized brain circuits connecting auditory and motor cortices. The vast majority of species known to have vocal production learning are birds, and only a small fraction of mammals — humans, pinnipeds, cetaceans, bats and elephants — show vocal production learning. Is seal vocal production learning closer to birdsong, or to human babies talking? Understanding or intending meaning is not relevant for vocal production learning, and neither Hoover nor most other animals exhibiting vocal production learning seem to ‘understand’ spoken language or the meaning of words. Nonetheless, vocal mimicry is impressive per se and represents a key building block of speech.The timeline of Hoover’s vocal displays suggests that he ‘imprinted’ on George Swallow’s vocalizations at a very young age. Hoover, like many birds, didn’t actually begin producing these learned sounds until he approached sexual maturity, suggesting that there may be a sensitive period for vocal learning in seals, as for many bird species. Although it is possible that only males learn sounds in harbor seals, the issue is too little researched for a definitive statement. Hoover’s example suggests that seals may learn their displays early in life, but only deploy this ability later, when sexually mature, to attract potential mates. Was Hoover a freak of nature or does he tell us something special about seals? Hoover was certainly unusual, but the basic machinery for vocal learning may be present in other harbor seals and pinnipeds. Three-week-old harbor seal pups can modulate the pitch of their voice without training, as we do when speaking or singing. Pitch plasticity requires laryngeal and breathing control — a key component of vocal production learning. Furthermore, seals and walruses can easily be trained to vocalize on command and can learn to roughly imitate both melodies and vowels. Finally, grey seals can be trained to configure their vocal tract to modulate formants, the building blocks of speech sounds, and mimic human vowels. Vocal production learning may thus be widespread in pinnipeds, making them both vocally gifted mammals and promising animal models for understanding human speech. Why are Hoover and other pinnipeds key to understanding vocal learning and human speech? Vocal production learning is a prerequisite for spoken language: humans use it from birth to learn the sounds and words of their language, and vocal production learning thus may have played an important role in the origins of human speech. Understanding the evolution of speech requires a comparative approach, probing for presence or absence of the trait across species in the context of phylogeny. Mammalian vocalizations and human speech are based on three interacting anatomical components: lungs (which control intensity and duration of sound), larynx (which affects the pitch), and vocal tract (for timbre and vowels distinction). Fine-tuned neural control over all three components is required for human speech. At present, harbor seals are one of the few other mammals known to finely control all three components. Apes, our closest relatives, appear to lack key neural connections enabling fine control of their larynx and vocal tract, despite the anatomy of the vocal tract itself being adequate for speech. Pinnipeds use a similar vocal tract to ours and are more closely related to humans than most other species with vocal production learning. Hoover’s case prompted a small scientific revolution in the comparative study of vocal learning by showing that harbor seals are clearly capable of vocal production learning, including formant modification, but much further research and more controlled experiments will be necessary to fully understand these capabilities. But, Hoover may eventually be immortalized as one of the godfathers of mammalian vocal production learning research. /cms/asset/b7856ef6-8346-4c3f-adbb-926d97ad4bea/mmc1.mp3Loading ... Download .mp3 (0.08 MB) Help with .mp3 files Audio S1. Sounds produced by Hoover/cms/asset/caee0fa6-3f10-43ea-bfac-374bc3294664/mmc2.mp3Loading ... Download .mp3 (0.07 MB) Help with .mp3 files Audio S2. Sounds produced by Hoover/cms/asset/7b7921f1-f318-4cc5-9db8-178970649e13/mmc3.mp3Loading ... Download .mp3 (0.08 MB) Help with .mp3 files Audio S3. Sounds produced by Hoover/cms/asset/0677dbd5-4452-46d8-9c25-8bc070c66564/mmc4.mp3Loading ... Download .mp3 (0.07 MB) Help with .mp3 files Audio S4. Sounds produced by Hoover

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