During class, we have been discussing language development and how it is affected in individuals who suffer from intermittent hearing loss, blindness, Down's syndrome, and autism. Although we touched on some aspects deafness during class, I have grown to love the deaf community during the time I have spent volunteering at a camp for children who are deaf and hard-of-hearing (HOH) and I wanted to learn more about language development in children who suffer from these types of hearing impairments. Due to the sake of not wanting to write a book on the subject, I will limit my discussion on language development to individuals who have been deaf since birth.
Deafness and Hard-of-Hearing: What's the Difference?
According to Mirriam Webster Medical Dictionary, individuals who are "hard of hearing" or have a "hearing impairment" have a defective, but functional, sense of hearing, while those who are considered "deaf" are lacking or deficient in the sense of hearing. The Individuals with Disabilities Education Act further explains that individuals with hearing impairments can often detect and respond to auditory stimuli, such as speech, while those who are considered deaf are unable to perceive sound stimuli in any form.
While the difference may seem insignificant to the hearing community, there is a huge difference between the two in the deaf community and it would take more than a short blog entry to adequately describe the difference.
What Causes Deafness?
There are two categories that describe what can cause an individual to become deaf. "Acquired" deafness is caused by illness or injury and can affect language development in a multitude of ways, which is why I will focus primarily on "congenital" deafness.
"Congenital" deafness was present at birth and in 50% of cases is due to genetic factors. Congenital deafness can be a result of family history (one or both parents being deaf or carrying a gene that causes deafness), infections during pregnancy, and complications during pregnancy. Unfortunately, there is little data that describes congenital deafness, but the American Speech-Language-Hearing Association says it appears that between 4 and 11 children per 10,000 births suffers from profound hearing loss from birth.
How Does Deafness Affect Language Development?
Many people assume that because deaf people do not always communicate verbally, that they do not develop language like we do. However, nothing could be further from the truth. Different forms of sign language exist throughout the world, which utilize a combination of different hand gestures to indicate letters, words, and phrases, as well as distinct syntactic rules, to communicate. Many studies have also indicated that deaf individuals use the same brain regions to process sign language as we do when hearing spoken English. Because of the vast differences in how and when deaf children are exposed to sign language, it is difficult to compare the very early stages of language development.
First word/sign: in deaf children who have been exposed to sign language, their first use of a gesture to indicate a word normally occurs around the same age as a hearing child speaks their first word. Similar to hearing children, the deaf child's first word is normally of extreme importance as well, such as 'mom', 'dad', 'milk', etc. Unfortunately, in deaf children, vocabulary development is extremely delayed. Although they begin signing around the same time, even children exposed to sign language during infancy develop vocabulary at a slower rate than hearing children. For deaf children not exposed to sign language, their vocabulary comprehension rates are typically between and two and four years behind those of their hearing peers.
Combining two words/signs: Similar to when infants depict their first word, the combination of two words occurs at similar times in those children who have been exposed to sign language and hearing children - around two years of age. However, for children not exposed to sign language, they may not have produced their first word at this point.
Syntactic Competence: Unlike in hearing children, most deaf children do not generalize syntactic rules they have learned (such as "I runned fast"). Instead, deaf children learn rules individually and often take much longer to develop proper syntactic competence.
Fingerspelling: One event that does occur in deaf children but that does not have an equivalent in spoken language is fingerspelling, or using individual letters to spell out words. Fingerspelling is a natural part of communication for deaf children and often occurs long before the child can recognize the printed letters. For many children, they recognize the combination of hand shapes used to depict a word, instead of the individual letters used. This principle of recognizing overall shapes is the main reason programs such as "Baby Can Read" have been so successful.
Based on this information, it is clear that the developmental deficits normally associated with the deaf population are strongly influenced by when the child is introduced to sign language and how often it is used in their presence. In my experience, children suffering from congenital deafness who are born into families where parents or older siblings are also deaf have few deficits in language acquisition. On the contrary, in recent years, many programs have come out that utilize sign language in infants to help accelerate language learning because infants are normally able to control their motor functions, such as hand motions, sooner than they are able to control the muscles involved in vocalization. It is my hope that as hearing screenings for infants become more common, the differences observed in language development between deaf and hearing children will eventually disappear.