What is the sensitive period of FLA (Foreign Language Acquisition)? Is the sensitive period solely a biological phenomenon, a psychological one, or perhaps a combination? I shall explore these questions with consideration to neuroscience and psychology in this article, and formulate practical ideas for foreign language classroom teachers —such as EFL teachers in Asia.

It is a well-documented phenomenon that toddlers grow an excessive number of neurons, only to have them gradually pruned as they grow older. This is called pruning (see above). It seems that this event takes place to help ensure that only the most appropriate neurons and networks are selected to carry on the foundations of the child's cognitive development (Chechik, et al, 1999). Is it possible that our own learning follows a similar pattern during language acquisition? In light of other animals' selective synapse elimination (Knudsen, 2004), it would seem so. We are born with the capability to decipher, learn, and use any human language on the planet. However, we only learn the languages that we actually attempt to negotiate the world with, and in most cases we can only reach a so-called native-sounding pronunciation in any given language if we are exposed to that specific language at a young age. Is there a time when our brains decide to prune sensitivity (synapse elimination) to potential sounds and linguistic patterns that we do not use on a regular basis? Does the brain actually streamline its own linguistic networks in order to focus more attention to (and to therefore raise the amount of usable cognitive processing power for only) the most typical-to-the-given-context’s linguistic negotiation patterns? If that is true then it would seem that our brain is marvelously economical in this area as it does away with seemingly needless synapses (and networks). Considering the early pruning of 'weak' neurons in toddlers, and combining to it our knowledge of the known functions of myelination (the ability to create more speedy neuronal network connections by thickening the insulation around our more important neurons' axons) it certainly does seem plausible from a biological perspective that our bodies may benefit from having a sensitive period regarding second language (L2) learning. However, the verdict on the sensitive period, and the even more controversial “Critical Period”, is a long-standing debate, with evidence supporting both sides of the issue (Birdsong & Molis, 2001).

The above paragraph sheds some light on the plausibility of a sensitive period for L2 from a neuro-biological perspective. Is there a neuro-psychological perspective that can be considered, too? As a child receives input from the world, the brain makes analyses of the incoming data. This process lays down tracks of cognition that are unique to the given context, or the culture. These tracks can later form stronger networks that remain in the brain to help make future decisions when faced with similar contexts. In our massively socio-cultural existence, most children learn about their world not separated from, but fully integrated with external stimuli and linguistic features. For instance, most children do not learn about the functionality of crayons, scissors, and paper without at least some linguistic input from parents, peers, and/or teachers. In most cases, children are bombarded with lexical items regarding all aspects of their realm of existence. Because a child's personal understanding of their world is constantly being written and re-written (crafted by and manipulated by) the linguistic input that they happen to receive in concert with each socio-cultural context that they encounter the lexis with, it is my hypothesis that in most circumstances, our own cognitive processes regarding the concepts in our world become reliant on, and become largely inseparable from, lexical items that have been strongly associated with those socio-cultural experiences because those lexical items were instrumental in the formation of the analysis of those very experiences. They must therefore be an integral part of the cognitive network associated with those experiences. In other words, our lexically-based understanding of any given concept is often fused with the non-lexical aspects of cognition regarding the given concept. For example, you cannot think about the word "table" without eventually evoking other lexis on some level connecting to table and you cannot think about "running" without eventually evoking lexis regarding the act of running — and then at some point evoke an emotion regarding them. From this observation, I claim that our upper cognitive processes and our emotions are both typically inseparable from our own first language’s lexical items. In a nutshell, our understanding of the world is massively fused with our first/main language.

Then, what of L2 learners? The answer is much more complex. First of all, what is the definition of an L2 learner? The outcomes of such research would vary widely with age and the amount of contextual support -but perhaps more importantly, for such learners, their entire developmental range is what we must ponder, not just isolated instances in time and context (Murphy, 2009). These points are unpacked across the following paragraphs.

According to Fischer's Dynamic Skill Theory (1980, 2006)(see Fig. 1), and my own research in the cognitive development of Japanese students (Murphy, 2009), with proper contextual support, children are capable of cognition at the "abstractions" level beginning around or slightly before the onset of puberty (10-12 or older). Before that level of cognition is the "representations" level. What potential meaning does this have in regard to L2 learning?
If a child in even a semi-bilingual/bicultural context is given opportunities to manipulate and negotiate the meaning of L2 representations (the semantics of concrete items of their world in L2) while they are still developing most of their own basic L1 representations (concrete items of their native world), they will most likely have authentic intrinsic psycho-social and cultural reasons to acquire the L2 representations as they experience them in tandem with their still-developing L1 representations. This will likely continue as long as they are in an L2 rich context that provides them with meaningful L2 input/output opportunities. However, if a child is put in an L2 rich context when the child of 10-12 years of age or older, and has consequently become capable of realizing cognition at the level of abstractions (and therefore has naturally lost some their keen focus on building representation level pragmatic neural connections), he/she may no longer have strong intrinsic motivation to acquire the L2 as a fundamental basis for unraveling the mysteries of their world, potentially making the L2 a foreign/alien aspect of the child, not a native one.

Even considering the intricacies and dynamism of the minor daily ups and downs in cognitive skill development, or micro-development (Schwartz & Fischer, 2005), I hypothesize that when a child grows accustomed to cognitive functioning at the abstractions levels, lower level cognition could literally seem like child's play in many instances, and therefore not be regarded as part of a very enticing learning experience. This point is noteworthy.
Moreover, I believe the potential negativity toward lower level cognitive activities gets stronger with age, which is why although micro-development is very much a reality even for adult language learning, adult language learners are seldom seen playing with wooden ABC blocks and/or seen moulding clay animals in language classrooms, even though such activities have the potential of being beneficial (Call, 1999; Hirsh-Pasek, 2006). However unfortunate it may be, it would seem that a significant portion of adults are too proud to actively and openly attempt to “regress” to lower states of cognition for the sake of more naturalistic L2 acquisition, even though it could be beneficial for them.

Not only might adults resent what may seem like child's play, perhaps much more importantly, they may have difficulty with the process of re-perceiving the world around them. I believe this second barrier is more difficult to overcome than the first one. Psychologically, having to re-perceive the world from the L2’s context (culture) could be unnerving and perhaps even devastating for some adults. From my own experience, I can say that many adults, somewhat understandably, don't seem to feel comfortable about actively engaging in the deconstruction of the very foundations of their own worldly (and in some cases, spiritual) enlightenment that has been built up throughout their lifetime in tandem with their L1s -simply for the sake a acquiring an L2 at a native-like level. I see this as a major psychological impediment that is perhaps the key component of the sensitive period issue.

Although biological and psychological aspects work together to form the so-called sensitive period for L2 learning, I see the psychological side to be more of a significant issue for teachers because I hypothesize that if the psychological issues of the sensitive period are skillfully tended to, then the biological issues may, to some extent (due to our remarkable brain plasticity), take care of themselves. I further hypothesize that the opposite will not hold true — a brain that is biologically still open to native-like L2 acquisition after puberty will not automatically provide the learner with the psychological plasticity to be more open to the notion of completely re-perceiving their world for the sake of L2 acquisition. For these reasons I believe teachers should focus on the positive aspects of effective pedagogies in the L2 classrooms that rely on brain plasticity and positive change rather than dwelling on the fact that there may be a damning biological issue at play regarding L2 acquisition timing.

So, how can this knowledge be used in the L2 classroom? Since many adults (both students and teachers) somewhat automatically attempt to tackle language learning with grammar-analysis/translation pedagogy in conjunction with rote-memorization, yet typically (because they are adults) do not heavily enough employ the faculties of the amygdala and hippocampus enough through "strong emotion” activities such as games, a simple yet potent suggestion I would like to make is to put less emphasis on computer-like rote memorization, Grammar-Translation, and "Presentation, Practice, Production [PPP]" style pedagogies. And instead put more emphasis on play and real-time "negotiation of meaning" in conversations based in real-life socio-cultural applications. In short, I recommend activities that involve fun-for-adult games, game-like play in the classroom, and engaging discussions that elicit real emotions concerning egocentric matters. In this way, adults may be able to run though dynamic stages of micro and macro development without even noticing they are doing so, therefore achieving their linguistic goals without bruising their adult pride.

In this paper, I have briefly examined the sensitive period of SLA from a biological and psychological point of view. I came to the conclusion that, it may be more beneficial to downplay the possible negative biological aspects of the sensitive period , and to focus efforts on the positive aspects of brain plasticity. I believe brain plasticity in L2 contexts may be positively affected by pedagogy inclusive of game play and egocentric discussions that connect with real emotions in the classroom rather than non-personal, overly analytical methodologies, even though adults may initially show a stronger preference for the latter.