This is by no means a full consideration of all existing exceptional circumstances for language development; rather it is a selection of the cases which I find most revealing to gain insight into normal language development. Indeed, in the light of the aforementioned exceptional circumstances, we will be able to draw understandings about language development in its unexceptional nature, such as its relationship to environmental factors (I) and to other cognitive devices (II).
First of all, exceptional circumstances can provide important evidence relevant to the role played by the verbal environment in child language acquisition. Neglected children, hearing children brought-up by deaf parents, bilingual children, and twins, are all faced to a certain form of restricted verbal stimulation. For instance, Marie Mason (1942) reported a case that concerned a neglected child, Isabelle, who had been kept in seclusion with her deaf and mute mother because she was illegitimate.
They spent their time in a dark room shut away from the family who had rejected them, and Isabelle was completely deprived of language until she gained her freedom at the age of 6. Children of deaf parents are also limited in their exposure to spoken language, although in the context of otherwise normal social, communicative and environmental stimulation. As for children who are brought-up bilingual and as twins, verbal stimulation is similarly impaired, the former because their exposure to one particular language is reduced ecause they must deal with two languages simultaneously, and the latter because one family’s linguistic resources are shared between two infants in the same developmental stage. Yet, just as Isabelle went on to develop normal language in only 18 months’ time after gaining her freedom (Skuse, 1988: 33), children of deaf parents, bilingual children, and twins, also develop normal language over time, albeit the adverse circumstances. This provides evidence of resilience of language acquisition.
Indeed, the fact that these children, despite such unfavourable circumstances, ultimately achieve linguistic proficiency (not unlike an ordinary child) tells us that children learn language despite a restricted language input, meaning that innate language abilities must have a substantial role in normal language acquisition. In this sense, exceptional circumstances indicate that the principles of language development advocated by behaviourists are quite inadequate to explain how the child develops language, and provides evidence in favour of Noam Chomsky’s theory of Universal Grammar.
Conversely, however, exceptional circumstances do provide some evidence of the importance of the verbal environment for normal language development. For instance, Genie, another neglected child who was discovered at 13 years of age after having been locked in a small room and beaten by her father whenever she uttered a sound, never fully recovered from the deprivation of language in her early years. Although she is now 55 years-old, she never acquired true linguistic competence.
This gives evidence for the existence of a time window during which external influences have a significant effect. Just as songbirds will learn to sing the appropriate song for their species only if they hear that song in the first few weeks of life, there is a critical period for the child to successfully develop language” (Bishop & Mogford, 1988: 252). This ‘critical period’ is set from birth to sometime between 5 and 7 years of age depending on the individual, which is why Isabelle –who was 6 when liberated– developed language readily, while Genie –who was 13– did not. Therefore, exceptional circumstances provide insight into a critical period for language development after which failed experiences in infancy cannot be compensated.
Moreover, exceptional circumstances can also provide insight into the relationship between language and cognition. In this section, we shall consider the case of children affected by Williams syndrome. Williams syndrome is characterized by a sophisticated use of language with complex syntax and adult-like vocabulary in individuals who otherwise demonstrate no evidence of concrete operational behaviour on Piagetian tasks, and whose overall level of mental development is below that of a 7-year-old (Jones & Smith, 1988: 248).
In other words, Williams syndrome children are mentally retarded, yet they demonstrate impressive lexical semantic abilities, complex expressive morphology and syntax, and good metalinguistic skills. For instance, three Williams syndrome adolescents were investigated: Van (age 11), Crystal (age 15), and Ben (age 16). Their full-scale IQ scores on traditional intelligence tests were: Van, 50; Crystal, 49; and Ben, 54. However, their scores on formal tests of language were higher than performance on non-language cognitive tasks (Bishop & Mogford, 1975: 182).
This relative sparing of language in the face of other cognitive impairments is particularly revealing about the relationship between language and cognition in that it implies that there is dissociation between language and other cognitive functions. Similarly, it may be particularly striking that, in patients of global aphasia, which is a severe language disorder, other cognitive skills remain functioning, affirming that language faculty is indeed a separate domain (Saffran et al).
Therefore, the exceptional case of Williams syndrome children, and the rather converse instance global aphasia, indicate that normal language development is not directly related to intelligence, hence why language is acquired rapidly and uniformly by all ‘normal’ children, irrespective of intelligence. In conclusion, language development in exceptional circumstances stands as a window into the analysis of normal language development.
In the words of Gary Dell: “the inner workings of a highly complex system are often revealed by the way in which the system breaks down” (Baars, 1992: 5). Indeed, throughout this essay, the study of exceptional circumstances has provided us with evidence that, although language input has an important role in language development, it may be limited, given the Poverty of Stimulus argument. The study of exceptional circumstances has also evidenced the existence of a critical period for language development and made the issociation between language and other cognitive functions clearer. Nonetheless, one must bear in mind that a more in-depth study of exceptional circumstances, for instance one that would take into account infantile autism or Down syndrome children, would certainly provide us with further information about the components of normal language development. Unfortunately, given the time limitations for the realization of this essay, these aspects will be left for others to analyse.