3.1 SLA Theories and L1 vs. L2 Acquisition

3.1 SLA Theories and L1 vs. L2 Acquisition

Understanding how human beings acquire and learn languages is central to effective English Language Teaching (ELT). The study of Second Language Acquisition (SLA) investigates the cognitive, psychological, and social processes that take place when an individual learns a language in addition to their mother tongue. For teachers preparing for the Cambridge TKT, mastering SLA theories provides the theoretical foundation for choosing appropriate classroom tasks, managing student expectations, and responding effectively to learner output.

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First Language Acquisition (L1) vs. Second Language Learning (L2)

A fundamental starting point in SLA is comparing how children acquire their first language (L1) with how individuals acquire or learn a second language (L2). While both processes involve internalising a complex linguistic system, the conditions, cognitive mechanisms, and outcomes differ significantly.

In L1 acquisition, infants and young children pick up their mother tongue subconsciously through thousands of hours of immersive social interaction. They are surrounded by highly contextualised, meaningful communication provided by caregivers who scaffold their understanding through facial expressions, intonation, and physical presence. Children are not taught explicit grammatical rules, nor are they tested on syntax; acquisition happens implicitly as a natural component of cognitive and social development.

In contrast, L2 learning typically occurs in older children, teenagers, or adults who already possess an established L1 system. L2 learners often have limited exposure to the target language—sometimes only two to four hours per week in a formal classroom setting. Furthermore, L2 learners bring mature cognitive abilities, abstract reasoning, and meta-linguistic awareness to the task. However, they may also experience affective barriers such as self-consciousness, anxiety, and fear of making mistakes, which rarely affect young L1 acquirers.

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Krashen's Monitor Model

One of the most influential theoretical frameworks in ELT is Stephen Krashen's Monitor Model, formulated in the late 1970s and 1980s. Krashen proposed five central hypotheses that explain the mechanism of SLA and directly inform communicative language teaching.

1. The Acquisition-Learning Hypothesis

Krashen argues that adults have two distinct ways of developing competence in a second language:

• Acquisition: A subconscious, natural process identical to L1 development. It occurs when learners focus on communication and meaning rather than language forms.
• Learning: A conscious process involving explicit study of grammatical rules, vocabulary items, and structural patterns.

According to Krashen, explicitly learned knowledge cannot be directly converted into spontaneous, fluent acquisition; it merely serves as an editor or monitor.

2. The Input Hypothesis ($i+1$)

This hypothesis states that language acquisition occurs exclusively when learners are exposed to comprehensible input—language that is slightly beyond their current level of competence. Krashen symbolises current proficiency as $i$ and the next developmental stage as $+1$.

• If input is at level $i+0$, no progress occurs because no new language is encountered.
• If input is at level $i+2$ or higher, the learner is overwhelmed because the language is incomprehensible.
• Input becomes comprehensible through contextual support, visual aids, mime, simplified teacher talk, and background knowledge.

3. The Natural Order Hypothesis

Krashen asserts that grammatical structures are acquired in a predictable, universal sequence regardless of the learner's native language or the sequence in which structures are taught in a textbook syllabus. For example, in English, the progressive suffix -ing and the plural -s are acquired long before the third-person singular -s (e.g., he walks) or possessive 's.

4. The Monitor Hypothesis

Explicitly learned rules act as an internal monitor or editor that alters or corrects utterances initiated by the acquired system. However, the monitor can only function if three conditions are met:

1. The learner has sufficient time.
2. The learner is focused on form and correctness.
3. The learner knows the rule.

Krashen categorises learners as monitor over-users (hesitant, overly anxious about correctness), monitor under-users (speedy but inaccurate, ignoring rules), or optimal monitor users (who use rules appropriately without disrupting fluency).

5. The Affective Filter Hypothesis

The affective filter is an emotional screen that can block input from reaching the language acquisition device in the brain. Psychological variables such as high anxiety, low self-confidence, and poor motivation raise the affective filter. When the filter is high, comprehensible input cannot pass through, preventing acquisition even when input is abundant.

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The Silent Period and Receptive Competence

When beginner L2 learners enter a new language environment, they often go through a silent period. During this phase, learners focus entirely on listening, processing auditory input, and building their receptive vocabulary without attempting to produce spoken output.

Key ELT Concept: Respecting the Silent Period Forcing beginner learners to speak prematurely in the target language can raise their affective filter, causing severe performance anxiety. Effective teachers provide rich comprehensible input and allow learners to demonstrate understanding non-verbally (e.g., pointing, gesturing, matching pictures, using Total Physical Response) until they feel ready to produce spoken words naturally.

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Interactionist and Socio-Cultural Perspectives

While Krashen emphasises passive reception of input, interactionist theories highlight the active role of social conversation. Michael Long proposed the Interaction Hypothesis, arguing that two-way communication forces speakers to engage in negotiation of meaning when breakdown occurs.

When a native speaker or teacher converses with an L2 learner, they use conversational modifications such as:

• Comprehension checks: "Do you follow what I'm saying?"
• Confirmation checks: "Did you mean you bought three tickets?"
• Clarification requests: "Pardon? Could you explain what you mean by that?"

These modifications make input more comprehensible and push learners to produce pushed output (Swain's Output Hypothesis), forcing them to move from semantic processing (understanding gist) to syntactic processing (constructing accurate forms).

From a Vygotskian socio-cultural perspective, learning is mediated through dialogue within the Zone of Proximal Development (ZPD). A knowledgeable teacher or peer provides temporary structural support (scaffolding), enabling the learner to accomplish language tasks they could not yet perform independently.