Scientists have understood the importance of "critical periods" in the lives of organisms ever since Konrad Z. Lorenz discovered the need for geese to go through filial imprinting shortly after hatching. A critical period is generally defined as a specific time in an organism's life in which an organism must learn a certain behavior or be exposed to particular environmental influences in order to develop properly. Sometimes a critical period is described more loosely as an optimal time in an organism's development where a specific skill is most easily obtained. Although the results of Lorenz's experiment validated the concept that geese have a critical period for imprinting from their parents, the concept of critical periods in human beings has been a topic of debate for several years. Critical periods have been discovered in several human systems, but a topic still argued over is the presence of a critical period in language development. The study of language brings forth several questions about whether or not there exists a necessary or preferable time in human life for the acquisition of language.
A recent event in Hong Kong may provide some insight into whether or not exposure to language during certain years can significantly impact human language use. Last Tuesday, a mother of four children was arrested for child neglect. Her children had been beaten, were malnourished, had problems with development, were extremely underweight, and had never had the opportunity to go to school. The sons were found to only speak "baby language" despite the fact that they were aged three to seven years.
The language impairment of the children raises several questions. Were the children unable to speak properly because they had not been exposed to language in school or with their family? Would this damage be permanent, irrelevant to their future success, or impair future language development from occurring successfully? Would developmental problems be worse for the younger children or the older children. Did any of the children miss the possible critical period for language and would future learning of language and language related knowledge be a struggle for them?
A famous story that addresses the concept of a possible critical period for language is the story of Victor, the "Wild Boy of Averyon." Victor was found in the early 1800s in France. He had appeared to have lived in the wild for a long time and could not speak. Despite efforts to "civilize" Victor and to teach him to speak, little success occurred. Victor's story also brings forth important questions about language. He most likely had not been exposed to language in his childhood because of living in the wilderness. If a person does not hear, speak, or learn language as a child, is it impossible to learn it later in life because of never having been exposed? In Victor's situation, this seemed to be the case. But although stories like that of Victor may seem to support a potential critical period for language development, it is also important to recognize that other circumstances may have been involved. Most historians assume that Victor had been ostracized by his family and abandoned. Several historians and psychologists suggest that Victor was autistic, a condition that may have served as a reason for his family to abandon him. If Victor was autistic, other factors may have come into play, and his impaired language development may have occurred for reasons other than a lack of exposure to language as a child. Victor's story is interesting because no one can really be sure why he could not speak or learn to speak. The story was documented, but in the early 19th century, nothing was done to really discover why he had problems with language. It would be interesting to examine a modern day "Victor" in the presence of new ideas, experiments, and technology. More modern studies on other "feral" children have demonstrated that there indeed seems to be some type of important time before children hit puberty in which language needs to be acquired. Without exposure to language during that critical period, humans tend to be unable to communicate sufficiently.
Scientists seem to agree that unlike many animals (such as birds) who can communicate with another based on sounds known innately, humans need extensive experience with language in order to learn a language. Early experience has also been found to be important. Babies who are deaf generally do not begin "babbling" (producing speech-like sounds), unless they are exposed to a type of sign language that allows them to babble with their hands. Feedback that children can hear and understand seems to play a significant role in the development of language. Deprivation of this feedback can put a stop to language development (as in the deaf children), and make future communication difficult. Another aspect of early experience in learning languages relates to the learning of a native language. As babies, humans can distinguish between all types of phonemes. However, as a baby is exposed to a certain language, the phonemes not associated with that language tend to fade out, and the baby only remembers those associated with its own language. If the same human tries to learn a language in the future that incorporates the forgotten phonemes, it is often difficult to produce and understand the sounds. Studies of language acquisition in babies support the concept that a critical period for language exists.
It appears that the early stages in human development provide important resources that aid in language development. But is the so-called critical period for language absolutely necessary for language acquisition, or just a preferable time in which language is acquired most efficiently? Are human beings who miss out on this critical period destined to a life of failure with languages and communications or can they in fact undergo language development throughout adulthood and the rest of their lives? Adults seem to learn new aspects of language everyday, but could they do that without the basis of language knowledge learned in childhood? If there is a critical period, is it a very specific time period (as seen with animal experiments), or does it vary from human to human, language to language, and culture to culture? Research seems to be supporting the presence of some type of critical period in learning language, but whether the critical period is a time that is absolutely necessary (as in the case of the geese) or whether it is a time of facilitated language development is still being examined.
Links I used:
"Sons 'Speak Baby Language'." http://www.news24.com/News24/World/News/0,,2-10-1462_2189820,00.html
http://en.wikipedia.org/wiki/Imprinting_(psychology)
"The Development of Language. A Critical Period in Humans." http://www.ncbi.nlm.nih.gov/books/bv.fcgi?indexed=google&rid=neurosci.section.1651
http://www.feralchildren.com/en/showchild.php?ch=victor
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Great post, very well researched! The question of critical periods is certainly an interesting one in psychology and neuroscience, and like you point out it is often difficult to differentiate competing hypotheses. One alternative to strict critical periods (the idea that children’s brains are more plastic or flexible before becoming fixed at a certain maturational stage such as puberty) is the idea that the brain is generally pretty flexible, but that as we experience life and learn new things (represented by patterns and networks of activity in the brain) it becomes harder to represent or distinguish information that we have not previously trained our brains to distinguish. Some researchers have suggested that this learning hypothesis can help explain the appearance of critical periods as well as related phenomena such as the infants’ ability to differentiate the phonemes of all languages while adults speakers often cannot differentiate certain phonemes in other languages that do not appear in their own. But of course, what can we as researchers do to differentiate these hypotheses? See Travis’ blog for more thoughts on this matter!
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