Babbling

Infants follow a general timeline of vocal developments in childhood.[14] This timeline provides a general outline of expected developments from birth to age one. Babbling usually lasts 6–9 months in total.[4] The babbling period ends at around 12 months because it is the age when first words usually occur. However, individual children can show large variability and this timeline is only a guideline.

From birth to 1 month, babies produce mainly pleasure sounds, cries for assistance, and responses to the human voice.[14]

Around 2 months, babies can distinguish between different speech sounds, and can make “goo”ing sounds.[14]

Around 3 months, babies begin making elongated vowel sounds "oooo" "aaaa", and will respond vocally to speech of others. They continue to make predominantly vowel sounds.[14]

Around 4 months, babies may vary their pitch, and imitate tones in adult speech.[14]

Around 5 months, babies continue to experiment with sound, imitating some sounds made by adults.[14]

Around 6 months, babies vary volume, pitch and rate. When infants are 6 months old they are finally able to control the opening and closing of the vocal tract, and upon obtaining this ability, infants begin to distinguish between the different sounds of vowels and consonants. This age is often distinguished as the beginning of the canonical stage. During the canonical stage, the babbling involves reduplicated sounds containing alternations of vowels and consonants, for example, "baba" or "bobo".[14] Reduplicated babbling (also known as canonical babbling) consists of repeated syllables consisting of consonant and a vowel such as "da da da da" or "ma ma ma ma".[15]

Around 7 months, babies can produce several sounds in one breath, and they also recognize different tones and inflections in other speakers.[14]

Around 8 months, babies can repeat emphasized syllables.[14] They imitate gestures and tonal quality of adult speech. They also produce variegated babbling. Variegated babbles contain mixes of consonant vowel combinations such as "ka da by ba mi doy doy".[16] Variegated babbling differs from reduplicated babbling in terms of the variation and complexity of syllables that are produced.[6]

Around 9–10 months, babies can imitate non speech sounds, and speech-like sounds if they are in the child's repertoire of sounds.[14] Infant babbling begins to resemble the native language of a child. The final stage is known as conversational babbling, or the "jargon stage". Usually occurring by about ten months of age, the jargon stage is defined as "pre-linguistic vocalizations in which infants use adult-like stress and intonation".[17] The general structure of the syllables that they are producing is very closely related to the sounds of their native language and this form of babbling significantly predicts the form of early words.[18]

Around 11 months, babies imitate inflections, rhythms, and expressions of speakers.[14]

By 12 months, babies typically can speak one or more words. These words now refer to the entity which they name; they are used to gain attention or for a specific purpose.[14] Children continue to produce jargon babbles beyond their first words.

Manual babbling is structurally identical to vocal babbling in its development.[19] Just as hearing and/or speaking infants babble with their mouths, infants who grow up with a sign language babble with their hands.[19] If a hearing infant has deaf and/or mute parents or parents who otherwise use a sign language, they will still imitate the signs that they see their parents displaying. This is evidence that manual babbling is possible in both hearing and deaf infants, and in both speaking and mute infants.[19]

All babies imitate with their hands the movements that they see. Typical gestures for example are raising arms to be lifted up, or grabbing/reaching to indicate wanting a bottle; these are used referentially.[20] In addition, infants who grow up with a sign language begin to make gestures that are distinct from all other hand movements and gestures.

After it was established that infants could babble with their hands and their mouths, the patterns in which productions occurred were studied. Speaking and signing infants follow very similar maturational paths in language acquisition.[18] Both go through a number of stages, and exhibit similar complexity in their babbling sequences. In studies where deaf and hearing children were compared, children learning sign language produced more multi-movement manual babbling than children who were not learning a sign language.[18] There are three main components of manual babbling. The hand gestures contain a restricted set of phonetic units, show a syllabic organization, and are used without reference or meaning. This is comparable to aspects of vocal babbling as mentioned above.[19] It is difficult to study manual babbling as often the manual activity can be mistaken as gestures rather than signs. When signing children are in fact babbling it will most often take place in front of their torso in a designated area that is called the phonetic space.[20] One of the most common forms of manual babbling is the extension and spreading of all fingers. This babble is also one of the first indicators that an infant will begin to make in manual communication.[18]

Children are able to produce signs correctly, which is important since many articulation tendencies of manual babbling transfer to the children’s early sign production.[18] Children acquire signs for the same concepts as speaking children's words, and in the same stage of development.[18]

Research has been conducted to determine whether or not infants with impaired hearing can demonstrate typical vocal sounds. Babbling can appear at the same age and in similar forms in hearing and deaf child, however, further continuation of babbling and speech development depends upon the ability for the child to hear themselves. For this reason, deaf children stop babbling vocally earlier than hearing children.[31] Babbling should appear if the child is exposed to language, but vocal babbling can be delayed or non-existent for deaf children.[18] It is not clear whether spoken language can develop fully without auditory experience.[21] Deaf children are not only significantly delayed in spoken language development in comparison to their hearing counterparts, but they also produce fewer noises.[32] This suggests that auditory experience is necessary in spoken language development. Some researchers have taken these findings as evidence against the hypothesis that language is an innate human capability.[26]

A number of solutions have been used for hearing-impaired humans to gain auditory experience, one of which is hearing aids; they can be used to help infants reach babbling stages earlier.[21] Cochlear implants have also been tested. Once the surgical implantation is complete, an infant has the opportunity to experience spoken language input. Once language has been heard, the infant begins to babble and speak in rhythmic patterns just as hearing infants do.[26]

Not only are songbird and human language parallel regarding neural and molecular factors, they also are similar in how their communication is initially produced. Observations about these similarities can be traced back to Charles Darwin and his studies. Avian and mammalian brains are similar in form and connectivity and there may even be a gene that is relevant to speech found in both organisms. The learning of a song is produced through a mix of interaction, experience, and predisposition. Young songbirds will imitate their species' call when presented with songs from their own and another species. They are physically capable of producing either song, but do not. Humans learn language through similar means, which is why this early vocalization in songbirds is considered babbling.[20]

Young male songbirds produce varieties of immature songs that are referred to as babbling because the immature songs precede those that are fully developed. As with humans, if these songs are reinforced with positive social feedback, they are more likely to recur. Since the females do not sing songs, they are in charge of providing the feedback. If females provide more social signals as feedback, males will develop more mature songs at a faster rate than other male birds. Young birds require reinforcement from adults in order to finalize their songs. Another relation to human infants is that the amount of vocalizations is not key, but rather the quality of the sounds that is retained and resembles the final produce of language.[33]

The physiology of the animal is important. The properties of the ear and vocal tract, as well as the brain regions used in analyzing and processing information are critical determinants of how song is interpreted and later produced. In studies using isolated birds that have not had exposure to song, they produce an abnormal ‘isolate song’ that nevertheless contains species-specific aspects. This shows that the neural pathways have predetermined features that allow for such a phenomenon to occur. The pathways are able to allow for plasticity of the songs that can be learned in the future.[20]

There is an important phase in development when song learning is best accomplished. This phase is called the ‘sensitive period’ and the amount of change that a songbird experiences in adulthood varies by species. Young birds have a production phase after a listening phase of development. The production of song is called ‘subsong’ where vocalizations resemble that of an adult as time passes. Memory for songs is able to form before the period where learning to sing occurs. Social interaction is important in vocal learning where non-singing females can even influence an infant through feedback.[20]

Pygmy marmosets have been studied and found to produce complex vocalizations 2–3 weeks after birth. Both sexes are capable of creating calls at a rate of 3 calls/second and each bout of calls can last up to 6 or 7 minutes. A normal series of calls by a pygmy marmoset contains approximately 10 different call types. This variety of call forms produced by this creature is comparable to babbling in human infants for a number of reasons. Like reduplicative babbling in humans, the call is often repeated several times before a new sequence of sounds is produced. The vocalizations gain attention from caregivers and provide practice for future vocal behavior. For these reasons, pygmy marmoset calls are seen as babbling behavior.[34]

There are a total of 16 call types in pygmy marmoset babbling language. Different calls serve different survival functions such as when desiring food, social interaction or during times of alarm. As human infants have, marmoset babies have higher rates of social interaction when producing babbling sounds. During the juvenile age, marmosets often regress back to babbling stages if a new infant is born. It is suggested that their production of babbling calls increases because they are seeking attention and social interaction. Another babbling occurrence during the juvenile age is the addition of territorial calls and mild threat vocalizations. Although babbling is important for practising adult calls during the juvenile age, babbling decreases with age in pygmy marmosets. Overall, babbling progresses through a series of stages from infancy to adulthood and slowly leads to the construction of adult calls.[34]

Babbling-like behavior in songbirds, humans and some nonhuman primates has been previously researched, but it has not been researched until recently in non-primate mammals. The sac-winged bat (Saccopteryx bilineata) is a social creature and the vocalizations that it produces depend on the social situation that the animal is in. This bat has a large repertoire of vocalizations with males being more vocal than females. Echolocation pulses, barks, chatters, and screeches are used in various social situations including courtship and territorial defense. Infants produce isolation calls if their mothers are absent, but the pups also produce vocalizations that mirror those of adults. Both sexes of infants babble, even though as an adult, the vocalizations are solely produced by males. Social context, mothers, and surrounding bats do not influence pups because the multiple vocalizations are combined regardless of the situation. Since there is not a social aspect correlated with the vocalizations, the productions of the sounds suggest that the pups vocalize for training. The pups repeat and combine adult vocalizations so that they resemble babbling in what humans, other primates and some songbirds do as infants. However, while human babbling increases social interactions, there are no social responses to babbling in bats. Babbling is common in infants that have a large repertoire of adult vocalizations to learn and this is seen in the pups of sac-winged bat.[35]