The next case study was discovered in 1970, when a nearly blind woman sought help for herself after captivity by her mentally unstable husband. Her thirteen-year old daughter, Genie, was admitted into hospital for malnutrition. Genie, like Victor, had no language when she was discovered. From the time she was twenty months old until her mother’s escape when she was thirteen, Genie spent her time strapped to a potty chair, and had minimal interaction and no talk. Her life and treatment before and after her discovery was documented by Curtiss (1977) and Rymer (1993). Genie did not talk at all when she was discovered. Four years later, she scored in the range of a normal five-year old on standardized vocabulary tests. However, her semantic skills far exceeded her syntactic skills. Her grammar was deficient in both production and comprehension (Curtiss 1977).
Similar cases of Chelsea (Curtiss, 1988, 1989) and Isabelle (Davis, 1947) illustrate the effects of long-term deprivation of linguistic input. Chelsea’s deafness was misdiagnosed as mental retardation and she was only fitted with hearing aids at age 31. By then, Chelsea could not even develop “the rudimentary aspects of grammatical structure” (p. 12) that were characteristic of Genie’s speech. Isabelle had been hidden away in an attic and given minimal interaction until she was discovered at age six, but could reach native-like fluency after one year of exposure. The differences between Genie and Isabelle suggest that a pronounced decrease in potential to acquire native-like proficiency in a first language occurs between the age of seven and puberty.
However, empirical data shows that deaf learners acquiring their first language, American Sign Language (ASL) from four to six years old show slight differences from full native-like proficiency, even after thirty years of using the language (Newport, 1990) while Ruben (1997) reported that hearing children who, due to otitis media, suffered from continuing hearing impairment in their first year of life and then recovered, scored significantly lower than controls for verbal memory and phonetic perception when tested at age nine. Based on these results, Ruben argued that a critical period for phonology may already terminate by age one and “insufficient early phonological input results in flawed semantics and syntactic capacities” (p. 117).
As can be seen from the cases highlighted, a delayed age of onset beyond puberty will result in less than native-like proficiency in the first language, if any language is attained in the first place. However, while it is tempting to accept such case studies as evidence for a critical period, one must also explore the validity of such cases. Firstly, in the cases of Victor and Genie, it is unclear whether the lack of language acquisition was due to a late age of onset. For example, the wrong training method might have been employed on Victor, or he might be physically impaired, resulting in the inability to acquire language. Genie was once diagnosed as mentally retarded as an infant (Rymer, 1993) but there was no follow-up to check if Genie were indeed retarded. Dichotic listening tests were also conducted and it was found that language was a right-hemisphere activity for Genie. A possible cause could be that the late AO prevented Genie from the using the left-hemisphere for language (which is better at language), but aphasia or some kind of brain injury might also have resulted in the loss of left-hemisphere activity. It was not clear from these studies if age was the definite cause of the inability to acquire native-like proficiency in first language.
As for the case of Isabelle, the statement that she reached native-like proficiency after one year may not be totally reliable, as it is not substantiated by detailed linguistic analysis. Moreover, the absolute absence of input during the first six years of her life was also not clearly substantiated. Since the case study of Isabelle is the only evidence that directly supports a critical age limit of six to seven years old, the vague conditions in the case study imply that the critical period could have a lower limit, in the cases that Isabelle had actually failed to attain native-like proficiency or if she had actually been exposed to language at a younger age.
Therefore, it could be seen that while the case studies highlighted a critical period does exist for language acquisition, it also leaves the question when the critical period is unanswered. Besides, because the data collected is sparse and often not well documented, it is difficult to obtain more information required to judge when this critical period lies. In these case studies, there could also be complications such as physical impairment, such that we could not attribute a decline in language proficiency beyond a certain period to the sole factor of age. Perhaps, amidst these considerations, “the only safe conclusions to be drawn from the multitude of reports is life in dark closets, wolves’ dens, forests, or sadistic parents’ backyards is not conducive to good health and normal development” (Lenneberg, 1967, p. 142).
References:
Curtiss, S. (1977). Genie: A psycholinguistic study of a modern day “wild child”. New York: Academic Press.
Curtiss, S. (1988). Abnormal language acquisition and the modularity of language. In F. Newmeyer (Ed.), Linguistics: The Cambridge survey: Vol. II. Linguistic theory: Extensions and implications. Cambridge, England: Cambridge University Press, 96—116.
Curtiss, S. (1989). The independence and task-specificity of language. In M. H. Bornstein and J.S. Bruner (Eds), Interaction in human development. Hillsdale, NJ: Erlbaum, 105—138.
Davis, K. (1947). Final note on a case of social isolation. American Journal of Sociology, 52, 432—437.
Gleitman, L. and Newport, E. (1995). The invention of language by children: environmental and biological influences on the acquisition of language. In L. Gleitman and M. Liberman (eds), Language: An Invitation to Cognitive Science. Vol. 2nd edition. Cambridge, MA: MIT Press, 1—24.
Lane, H. (1976). The wild boy of Aveyron. Cambridge, MA: Harvard University Press.
Lenneberg, E. (1967). Biological Foundations of Language. New York: John Wiley.
Ruben, R.J. (1997). A time frame of critical/sensitive periods of language development. Acta Otolaryngologica, 117, 202—205.
Rymer, R. (1993). Genie: A scientific tragedy. New York: HarperCollins.