Why Can't I Speak Spanish?: The Critical Period Hypothesis of Language Acquisition

Biology 202
2003 Second Web Paper
On Serendip

Why Can't I Speak Spanish?: The Critical Period Hypothesis of Language Acquisition

Stephanie Richardson

"Ahhhhh!" I yell in frustration. "I've been studying Spanish for seven years, and I still can't speak it fluently."

"Well, honey, it's not your fault. You didn't start young enough," my mom says, trying to comfort me.

Although she doesn't know it, she is basing her statement on the Critical Period Hypothesis. The Critical Period Hypothesis proposes that the human brain is only malleable, in terms of language, for a limited time. This can be compared to the critical period referred to in to the imprinting seen in some species, such as geese. During a short period of time after a gosling hatches, it begins to follow the first moving object that it sees. This is its critical period for imprinting. (1) The theory of a critical period of language acquisition is influenced by this phenomenon.

This hypothetical period is thought to last from birth to puberty. During this time, the brain is receptive to language, learning rules of grammar quickly through a relatively small number of examples. After puberty, language learning becomes more difficult. The Critical Period Hypothesis attributes this difficulty to a drastic change in the way that the brain processes language after puberty. This makes reaching fluency during adulthood much more difficult than it is in childhood.

The field of language acquisition is very experimental because scientists still do not completely understand how the brain deals with language. Broca's area and Wernicke's area are two parts of the brain that have long been identified as areas important for language. Broca's area is the left frontal cortex, while Wernicke's area is the left posterior temporal lobe. These areas are connected by a bundle of nerves called the arcuate fasciculus. Both Paul Broca and Karl Wernicke had patients with lesions with lesions on their brains. The problems caused by these lesions led to the discovery of Broca's area as the sight for the production of speech and Wernicke's area as tied to language comprehension. (2) The location of these areas, as well as the effects of anesthetizing one half of the brain have lead scientists to believe that language is primarily dealt with by the left hemisphere of the brain.

Recent studies have shown that activity in the planum temporale and the left inferior frontal cortex during acts of language are not unique to hearing individuals and therefore cannot be attributed to auditory stimuli. The same brain activity was shown in deaf individuals who were doing the equivalent language task in sign language. This adds more support to the idea of specific areas of the brain devoted to language. (3)

Noam Chomksy suggests that the human brain also contains a language acquisition device (LAD) that is preprogrammed to process language. He was influential in extending the science of language learning to the languages themselves. (4) (5) Chomsky noticed that children learn the rules of grammar without being explicitly told what they are. They learn these rules through examples that they hear and amazingly the brain pieces these samples together to form the rules of the grammar of the language they are learning. This all happens very quickly, much more quickly than seems logical. Chomsky's LAD contains a preexisting set of rules, perfected by evolution and passed down through genes. This system, which contains the boundaries of natural human language and gives a language learner a way to approach language before being formally taught, is known as universal grammar.

The common grammatical units of languages around the world support the existence of universal grammar: nouns, verbs, and adjectives all exist in languages that have never interacted. Chomsky would attribute this to the universal grammar. The numerous languages and infinite number of word combinations are all governed by a finite number of rules. (6) Charles Henry suggests that the material nature of the brain lends itself to universal grammar. Language, as a function of a limited structure, should also be limited. (7) Universal grammar is the brain's method for limiting and processing language.

A possible explanation for the critical period is that as the brain matures, access to the universal grammar is restricted. And the brain must use different mechanisms to process language. Some suggest that the LAD needs daily use to prevent the degenerative effects of aging. Others say that the brain filters input differently during childhood, giving the LAD a different type of input than it receives in adulthood. (8) Current research has challenged the critical period altogether. In a recent study, adults learning a second language were able to process it (as shown through event related potentials) in the same way that another group of adults processed their first language. (9)

So where does this leave me? Is my mom right, or has she been misinformed? The observation that children learn languages (especially their first) at a remarkable rate cannot be denied. But the lack of uniformity in the success rate of second language learning leads me to believe that the Critical Period Hypothesis id too rigid. The difficulty in learning a new language as an adult is likely a combination of a less accessible LAD, a brain out of practice at accessing it, a complex set of input, and the self consciousness that comes with adulthood. This final reason is very important. We interact with language differently as children, because we are not as afraid of making mistakes and others have different expectations of us, resulting in a different type of linguistic interaction. Perhaps that LAD processes those types of interactions better. There is not yet enough research to make a conclusive statement, but even the strictest form of the Critical Learning Hypothesis does not say that that language learning is impossible in adulthood. I guess that means doesn't get me off the hook. I'd better keep studying.

References

1) Learning Who is Your Mother, The Behavior of Imprinting by Silvia Helena Cardoso, PhD and Renato M.E. Sabbatini, PhD.

2) The Brain and Language Language page of the Neurobio for Kids websight.

3) Brain Wiring for Human Language Scientific American article.

4) Universal Grammar [Part 1] Forum area of Gene Expression websight.

5) The Biological Foundations of Language, Does Empirical Evidence Support Innateness of Language? by Bora Lee.

6) Evolution of Universal Grammar by Martin A. Nowak, Natalia L. Komarova, and Partha Niyogi.

7) Universal Grammar by Charles Henry.

8) A concept of 'critical period' for language acquisition, Its implication for adult language learning by Katsumi Nagai.

9) Brain signatures of artificial language processing: Evidence challenging the critical language hypothesis by Angela Friederici, Karsten Steinhauer, and Erdmut Pfeifer.

Comments made prior to 2007

i appreciate your frustration and share it with you. But I respectfully disagree with some of your analysis. You discount motivation. It is a huge factor. If you choose not to practice the language you are learning -- i.e. immerse yourself in it -- then you can only expect frustration. I remember when I took myself from knowing biblical hebrew to convesational. each step was very slow and i made imperceptible progress and many, many mistakes. I still hate the frustration i feel when making certain sounds in hebrew that i was not taught to do from a very young age. nevertheless, i learned modern hebrew because i wanted to learn it more than anything and i insisted on speaking it whenever possible. maybe this will help you or others. i mastered hebrew, not spanish. learning an additional language i am not motivated to learn will probably result in me sharing your frustration too ... Mordechai Pelta, 20 April 2006