Infants go through many stages of language acquisition, all the way from babbling to forming multi-word sentences. Do these stages occur in infants that are deaf or hard of hearing? If deaf infants were to babble the same way as normal hearing infants, it would suggest that phonetic inheritance in humans is something that we are born with, even without prior auditory experiences. If babbling did not occur in deaf or hard of hearing infants, it would suggest that auditory experience plays a significant role in phonetic inheritance.

This first study, “Babbling in canonical stage deaf and hearing infants,” by Oller and Eilers, talks about the four audition stages that occur in the first year of life in both hearing and deaf infants. The phonation stage happens around 0-2 months. This stage includes “comfort sounds” which includes what it sounds to be them trying to produce vowels . The “gooing stage” happens around 2-3 months, which provides a clearer production of vowels and precursors to consonants. The “expansion stage” happens around 4-6 months, the time where new sounds are usually produced. For example, they will produce yells, squeals, growls and isolated vowels. The “canonical stage” happens from 7-10 months, this is when there are well-formed syllables. This stage is critical because this  point symbolizes when infants can produce syllable function.

The study compares hearing infants with deaf infants and the data was collected from their first 10 months of life. This was collected through tape recordings and transcriptions of their babbling. Deaf infants were wearing hearing aids at the time of this study and, not surprisingly, not one of the deaf infants made it to the fourth canonical stage. However, no infants show developmental delay in areas other than speech and language.

The results of this study found that deaf infants show only a delay in reaching the canonical stage, if they do at all, even if they have been stimulated and exposed to the same auditory environment as hearing infants. Only part of this stage is reached because they are still able to perceive speech and language audibly even if they are hearing impaired. The only treatment that can be done to improve this is to try and stimulate the production of babbles.

Speech production in hearing infants is usually routine, following the steps that were previously mentioned. Another study, “Babbling and the lack of auditory speech perception: a matter of coordination?” by Florien, also tracks the vocalization in hearing and deaf infants, but this time over the course of 18 months, about the amount of time that it takes to complete all the stages. The mean age that a hearing infant started babbling was 30.8 weeks and deaf infants started to babble, at the earliest, 18 months of age. The babbling specifically focuses on “uninterrupted phonation combined with two or more articulatory movements.”

Uninterrupted phonation is the earliest production of phonetics in infants. Interrupted phonation combined with two or more articulatory movements is more complicated; both of these measures were tested on hearing and hard of hearing infants. The results were significantly different with a p value of <0.05. The results of this study show where the vocalizations actually differ .

Both hard of hearing and normal hearing infants are at the same developmental rate, but hearing infants use the two-sound production system, which contains both the phonatory system and the articulatory system. Deaf infants possess both of these systems but the problem occurs in when the two systems have to be combined, which is required for canonical babbling, posing trouble for the deaf infants.

Another study, “Babbling in the Manual Mode: Evidence for the Ontogeny of Language” by Petitto and Marentette, discusses the ontogeny of language, specifically in babbling. Ontogeny is basically the development of a single organism, in this case being the vocal tract. As previously discussed, babbling directly effects later language acquisition. This is another article that directly focuses on babbling between deaf and hearing infants, but this study also incorporates sign in addition to speech. Discussed is the importance of manual and vocal babbling and how that is achieved on a brain-based capacity. Babbling is the structure of language that is expressive, signed or spoken.

Similar to previous studies, this study focuses on five infants whose language development was video taped from the ages of 10 months – 14 months. The deaf infants acquired American Sign Language as their first language, and the hearing infants acquired spoken language as their first language with no exposure to American Sign Language. Both groups were tested identically.

The experiment with the hearing infants was analyzing their sounds, like in previous studies. However, the experiment with the deaf infants analyzed their gestures, which they counted as their babbling. In the manual babbling, the infants used hand shapes that are mostly found in ASL, focusing on the ones that were most common. Hearing infants babbled mostly syllables and deaf infants rotated “babbling” 13 signs. This study concluded that babbling is a result of brain based capacity and expression, no matter if they are hearing or deaf, because they can both be expressed. That language is the act of discovering your environment and expression what stimuli comes from that environment.

After learning about how babbling translates into signing in the previous article, the study, “How do deaf infants attain first signs?” by Takei, focus’s solely on the process of deaf infants first attaining signs. This study focused on Japanese Sign Language in deaf infants and how they come to learn their first signs. Acquisition tends to occur the same in both deaf and hearing infants. The first signs that are recognizable by the parents of deaf infants occur from 8 months – 12 months, with more advanced signs occurring at about 18 months, parallel to hearing infants.

This particular experiment observed deaf infants’ hand signs, and broke them into categories of signs, communicative gestures, manipulating, and nonreferential gestures. This  categorization helped them break down and decipher what was being used for communication in the form of “words”, object recognition, or if they even meant anything at all. The results of this study again, matched up with the language acquisition stages of hearing infants.

They concluded two features of nonreferential gestures that the deaf infants produced. The first being that these signs that didn’t have a message behind them were observed 3 or 4 months before actual recognizable signs were observed. This is similar to hearing infants because the nonreferential gestures represent the canonical babbling stage, which is again observed a few months before the first word is produced.

In the study “Infant vocalizations and the early diagnosis of severe hearing impairment,” by Ollers and Eilers, it focus’s on the canonical babbling stage, it discusses how this stage can determine a potential risk in hearing impairment and speech development. Diagnosing hearing loss at the infancy stage is common, and often infants are not properly provided with the resources that could help them acquire at least some language, because infancy is a key period in this development.

This particular study is further evidence that in hearing infants, if the canonical stage is delayed they are at risk for a speech developmental delay. This could be key in the diagnosis of a potential hearing impairment in an infant. There is also no way that hearing infants and deaf infants can go through these stages at the same rate/in the same way. The key conclusion of this study is if the stages of speech development are not there, the infant may have a severe hearing impairment.

After all of these studies and experiments it is safe to conclude that yes, both deaf and hearing infants have the ability to babble, and they both reach the same stages of language development, just in different ways. Whether it is vocally or manually, they both have the ability to develop at the same rate, with the same brain capacity, even if it differs in expression.

Koopmans-van Beinum, F. J., Clement, C. J., & van den Dikkenberg-Pot, I. (2001). Babbling and the lack of auditory speech perception: A matter of coordination?. Developmental Science, 4(1), 61-70. doi:10.1111/1467-7687.00149

Oller, D. K., & Eilers, R. E. (1988). The role of audition in infant babbling. Child  Development, 59(2), 441-449. doi:10.2307/1130323

Oller, D. K., & Eilers, R. E. (1994). (2007, November 27). Retrieved December 06, 2017, from http://www.sciencedirect.com/science/article/pii/S0022347694703035

Petitto, L. A., & Marentette, P. F. (1991). Babbling in the manual mode: Evidence for the ontogeny of language. Science, 251(5000), 1493-1496. doi:10.1126/science.2006424

Takei, W. (2001). How do deaf infants attain first signs?. Developmental Science, 4(1), 71-78. doi:10.1111/1467-7687.00150