Introduction
Despite a large body of evidence supporting Lenneburg’s Critical Period hypothesis as the main decisive factor for language development, case studies like Genie (Yule, 2010) have shown how other factors are able to influence the LAD if an individual has been severely traumatised.
There are several definitions of the Critical Period. From Lenneburg’s linguist perspective, the Critical Period is the specified stage in which the Language Acquisition Device (LAD) can work to its full capacity. The LAD is built into Chomsky’s innatist perspective, in which infants are biologically predisposed to acquiring a language (Buitrago, no date). On the other hand, Sengpiel argues that the Critical Period is when the brain’s features are shaped through its plasticity, along with the impact of our own personal experience and surroundings (Sengpiel, 2007). Therefore, this supports the argument that the Critical Period is a decisive factor in the development of language, because Sengpiel is arguing that our biological features (genes, brain structures, etc) are controlled by environmental factors e.g. upbringing, etc (2007). As well as this, from Bowlby’s psychological perspective, the critical period’s (also known as the sensitive period in humans) duration is up to two years old (McLeod, 2007). Maternal deprivation occurs when an infant fails to form a bond with its mother – who is seen as the most important attachment figure – and is likely to have a lower IQ than usual or no language development (McLeod, 2007). This links back to Genie, who was unable to produce speech, due to the abuse she suffered at the hands of her father (Yule, 2010). Additionally, the fact that Genie failed to form a bond with her mother (Yule, 2010), is indicative of the fact that the Critical Period is a decisive factor when it comes to learning a language.
However, the brain must also be considered when looking at the development of language. Firstly, the brain’s plasticity allows new, stronger connections to be formed, whilst older and weaker ones can be deleted. For example, the use of a homologous area in the opposite hemisphere to which a brain function is localised, allows for the function to continue to work if an area is damaged in the brain. As well as this, a lateralised view of the brain presents the left hemisphere as the language centre of the brain, whilst the right hemisphere is usually involved in facial recognition. Evidence that is provided through the use of brain imaging procedures are usually reliable, due to high levels of objectivity. With this in mind, it is harder to generalise findings onto the wider population (much like with case studies), due to low external validity – which essentially means that tasks are unrepresentative of reality in research procedures.
Throughout this essay, I will analyse the extent to which the Critical Period is a decisive factor in language development, as well as cognitive and psychological factors too, which I have briefly mentioned above such as brain lateralisation and Bowlby’s stance on the Critical Period.
Critical Period as a decisive factor
As I stated before, Lenneburg believed the critical period to be a fixed duration up to the start of adolescence, in which the LAD is able to work fully. The LAD is formed of all the general criteria that is consistent in all languages. It forms part of Chomsky’s innatist theory, which is centred on the belief that children are able to produce many utterances without the knowledge of grammar and syntax. This means that the critical period could be decisive in language development, because the innate feature of the LAD suggests that we are all born with the intent to produce speech. Since the critical period is up to the pubescent period, it is not necessary for children to acquire a language, but after this period, it becomes incredibly difficult for children to develop the ability to produce language with complexity. In the case of thirteen year-old Genie, who was severely abused by her father and locked up for her whole life, she was not able to acquire a language due to being forced to stay silent (Yule, 2010). This provides support for the critical period being a decisive factor, because Genie’s case study illustrates what happens when the LAD does not work to its full capacity. Other research evidence to validate this argument is from deaf people who use American Sign Language (ASL) as a means of communication (Guasti, 2002). Singleton and Newport’s research (cited by Guasti, 1994) found that ‘production and comprehension of ASL verb morphology by congenitally deaf individuals exposed to sign language from birth’ had a weaker score if they acquired ASL later on (Guasti, 2002). For example, those who learnt ASL after the age of 12, struggled the most with the task (Guasti, 2002), which provides supporting evidence for the fact that the critical period can determine how quickly you can develop language, whether that be verbal or non-verbal forms. Although there is a lot of reinforcement for this argument, the samples used in these research studies are abnormal, and therefore harder to generalise to everyone in society. This is because Genie was traumatised from her childhood experience, and so the conclusions made from her case study are too personalised. As well as this, the sample of deaf individuals in Singleton and Newports research (cited by Guasti, 1994), are unusual. Therefore, this questions the extent to which the critical period is a decisive factor for language development, as the research evidence could be suggesting that this argument only applies to these certain groups of individuals, instead of the wider population.
Moreover, Genie was also able to communicate through simple syntax eventually (Yule, 2010), which refutes the idea of the critical period being a decisive factor for language development. This is because she was still able to gain some language abilities, despite not acquiring language during the critical period. Therefore, this suggests that there are definitely other factors at play that should be considered (other than the critical period hypothesis), such as neurological areas in the brain.
The brain as a decisive factor
Language is located in the left hemisphere of the brain, which is supported by Sperry’s split-brain research (Ziganshina, 2017). Case studies such as Phineas Gage, support the fact that there are structures in the brain which affect language development – his frontal lobe was destroyed and so he was unable to make decisions (Yule, 2010). Broca’s area, localised in the left hemisphere, is involved speech construction, and Wernicke’s area which is also localised in the left hemisphere is involved in interpreting speech (Yule, 2010). Damage to either Broca’s area can cause Broca’s aphasia, which means that grammar is missing from the speech, as well as morphemes (Yule, 2010). Then we have Wernicke’s aphasia due to damage to Wernicke’s area which reduces the comprehension of speech from the sufferer (Yule, 2010). Those with this type of aphasia can also have anomia, which means that sufferers will struggle with using the correct words to form grammatical sentences (Yule, 2010). Since the brain is a biological structure, is presents a very determinist perspective of how language develops, suggesting that we have no control over this process. This is a strong rebuttal for the critical period being the decisive factor, because the localisation of language in the brain demonstrates how language is controlled and formed. Therefore, it should not be agreed that the critical period is the ultimate factor in concluding whether individuals have the ability to acquire their first language. On the other hand, it should not be assumed that the brain is the main element for language development either, as Genie was able to use her right hemisphere to produce language using simple syntax – so this localised view of the brain should be reconsidered if there are further intricate structures for language in the whole brain (Yule, 2010).
Psychology as a decisive factor
It is also worth mentioning that Bowlby included the critical period in his Monotropy theory. Within the first two years of life, an infant should have formed a unique bond with their mother, who is seen as the main caregiver (McLeod, 2007). Failure to form this bond can have severe implications on the child’s language development, and intellectual development too (McLeod, 2007). This is linked to Genie, who was not allowed to form a relationship with her mother, and as we know, she could not form complex, grammatical structures (Yule, 2010). It can be argued that the psychological effects of the abuse she suffered, were the decisive factor of her reduced language development, because she failed to attach to her main caregiver. However, Lenneburg’s perspective of the critical period tells us that psychological factors can play a part in this explanation, since these factors would have reduced the capacity of Genie’s LAD, and therefore reduced her ability to develop a language. This means that the critical period can be a decisive factor for language development, especially if it is slowed down by these psychological factors.
Conclusion
Whilst there is a good amount of supporting evidence for Lenneburg’s critical period hypothesis, other factors such as the brain and attachment in psychology are also paramount for language development. As the brain is continuously being studied, it should not be assumed that this biological structure is the decisive factor – there is so much more to be discovered. Even though I am refuting this idea that the critical period is a decisive factor for language development, I am acknowledging the implications mentioned above if no language is learned during this time. The psychological affects mentioned above can be extreme, and therefore it should not be assumed that language development is the only process that is implicated. There should be a balanced argument for the process of language development, but until then, this stance must be rejected as research into language development continues.