Second Language Learning Theories: A Comprehensive Overview

The study of second language acquisition (SLA) seeks to explain how individuals learn a second language, building upon their existing knowledge of their first language. This interdisciplinary field draws insights from linguistics, sociolinguistics, psychology, cognitive science, neuroscience, and education. These diverse perspectives can be grouped into four major research strands: linguistic, cognitive, socio-cultural, and instructional dimensions of SLA. While each strand has a distinct focus, they all aim to identify conditions that facilitate successful language learning.

Historical Development of SLA Theories

Pinpointing the exact beginning of SLA as a field is challenging due to its interdisciplinary nature. However, two publications are widely recognized as foundational to the modern study of SLA: Corder's 1967 essay, "The Significance of Learners' Errors," and Selinker's 1972 article, "Interlanguage."

The 1970s saw research expanding on the ideas of Corder and Selinker, while also challenging behaviorist theories of language acquisition. This included investigations into error analysis, studies of transitional stages in second-language ability, and "morpheme studies" that explored the order in which learners acquired linguistic features.

By the 1980s, Stephen Krashen's theories, known as the Input Hypothesis, gained prominence. Krashen proposed that language acquisition is primarily driven by comprehensible input - language that learners can understand. This model significantly influenced both SLA research and language teaching practices. During this period, other theories emerged, including Michael Long's Interaction Hypothesis, Merrill Swain's Output Hypothesis, and Richard Schmidt's Noticing Hypothesis. Additionally, Elaine White's work on learner competence and Manfred Pienemann's application of speech processing models and lexical functional grammar to explain learner output made notable contributions.

The 1990s were marked by two main research areas: linguistic theories of SLA based on Noam Chomsky’s Universal Grammar and psychological approaches such as skill acquisition theory and connectionism. This era also saw the development of new frameworks, including Processability Theory and Input Processing Theory. Moreover, sociocultural theory, which explains SLA in terms of the learner's social environment, and approaches influenced by complexity science were introduced during this period. These trends continued into the 2000s, with research remaining divided between linguistic and psychological approaches.

Key Concepts in SLA

Input and Intake

Learners' primary source of information about the target language is direct exposure to it, referred to as "input." When learners process this input in a way that contributes to learning, it becomes "intake." However, the input must be comprehensible to the learner. Krashen's monitor theory suggests that language input should be at the "i+1" level, slightly beyond the learner's current understanding. This input is comprehensible but contains structures not yet fully mastered. Critics argue that "i+1" lacks a clear definition and that factors beyond structural difficulty can influence whether input becomes intake.

Krashen's Input Hypothesis and Monitor Model

Krashen's Input Hypothesis posits that language acquisition occurs when learners receive input that is just beyond their current L2 competence, termed “i+1.” Krashen also distinguishes between "acquisition," a subconscious process of picking up a language like children do with their first language, and "learning," the conscious and intentional study of language features common in traditional classrooms. He views these processes as distinct with minimal interaction.

In contrast to emergentist and connectionist theories, Krashen adopts an innate approach, applying Chomsky's Government and Binding Theory and the concept of Universal Grammar (UG) to second-language acquisition. He proposes a Language Acquisition Device that uses L2 input to define the parameters of the L2 within the constraints of UG and to increase the learner's L2 proficiency.

Krashen's Affective Filter Hypothesis states that anxiety can hinder second language acquisition. A high degree of anxiety when receiving input can cause a mental block, preventing intake.

Input enhancement, which involves modifying input to highlight important linguistic features, has been a focus of research. This might involve bolding vocabulary or adding marginal glosses in a text.

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Interaction and Output

Long's Interaction Hypothesis emphasizes the importance of interaction in language acquisition. Similar to Krashen's Input Hypothesis, it asserts that comprehensible input is crucial. Long focuses on exchanges between teachers and learners or among learners, arguing that adjustments made during these interactions facilitate SLA. Through interaction, the difficulty of content can be adjusted to the learner's level, promoting effective learning.

Merrill Swain's Output Hypothesis suggests that meaningful output is as essential as meaningful input for language learning. Although some studies have not found a strong correlation between the amount of output and learning, the hypothesis highlights the importance of actively using the target language. Recent research has expanded to include insights from socio-cultural theory.

Attention and Cognitive Processes

Attention is considered a key factor in successful language processing. Several theories explore how learners use their internal L2 knowledge to understand input and produce output. One perspective suggests that L2 proficiency is acquired similarly to other complex cognitive skills.

Automaticity, the ability to perform a skill without conscious control, results from proceduralization. Anderson's model of skill acquisition in cognitive psychology suggests that individuals use procedures to apply declarative knowledge to solve problems. With practice, these procedures become production rules, allowing for problem-solving without accessing long-term declarative memory. DeKeyser's research supports the application of this model to L2 automaticity, showing that learners develop proficiency in morphosyntax through practice, following a typical learning curve for cognitive skills.

Linguistic Theories of SLA

Universal Grammar (UG) and the Fundamental Difference Hypothesis (FDH)

Chomsky's theory of Universal Grammar (UG) has significantly influenced the field of linguistics. The Fundamental Difference Hypothesis (FDH), proposed by Bley-Vroman (1989), suggests a distinction between L1 and L2 acquisition. According to the FDH, L1 acquisition is guided by UG and the innate language acquisition device, while L2 acquisition relies more on general cognitive mechanisms like problem-solving and memory. Adult learners might lose access to UG, which could explain the persistent errors and slower progress often seen in L2 learning compared to L1 acquisition. Studies showing differences between child and adult language learning, especially in syntax and morphology, support the FDH.

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Other Linguistic Hypotheses

The Wild Grammar Hypothesis suggests that the initial stages of L2 interlanguage are not constrained by Universal Grammar (UG). The Missing Surface Inflection Hypothesis (MSIH) proposes that the omission of inflectional morphology in L2 learner output reflects difficulties in mapping grammatical representations onto surface forms, rather than deficits in learners’ underlying grammatical knowledge. It explains that competition occurs between morphemes inserted in morphology, and in such cases, the underspecified form is incorrectly selected.

The Representational Deficit Hypothesis (RDH) and the Interpretability Hypothesis (IH) are related theories addressing challenges faced by adult learners in acquiring certain grammatical features in their L2. Both claim that adult L2 learners struggle to acquire grammatical features in the L2 that are uninterpretable and absent in their L1. These uninterpretable features are syntactic elements that serve a grammatical function but lack semantic meaning, such as agreement, tense, or case markers. According to the RDH, adult learners lose full access to UG and therefore cannot fully represent new features in their interlanguage if those features are absent in their L1. Both hypotheses converge on the idea that L2 acquisition in adulthood is constrained by the availability of UG and the learners’ L1 grammar. They agree that uninterpretable features absent in the L1 are particularly challenging, leading to persistent errors or incomplete acquisition in the L2.

The Feature Reassembly Hypothesis (FRH) emphasizes the challenge L2 learners face in reorganizing their L1 linguistic features to match the configurations of the L2. Unlike the Valueless Features Hypothesis, this approach acknowledges that learners bring feature values from their L1, but these values often need to be restructured to accommodate the target language. This hypothesis has been praised for explaining difficulties in L2 acquisition, particularly when L1 and L2 grammars diverge significantly.

The Interface Hypothesis explores the challenges learners face at the intersection of syntax and other linguistic domains, such as semantics and pragmatics. While UG may facilitate the acquisition of core syntactic structures, learners often struggle with interface phenomena that require the integration of multiple linguistic modules. The Interface Hypothesis has gained attention for addressing advanced stages of L2 acquisition, where subtle pragmatic or contextual errors persist.

The Bottleneck Hypothesis suggests that certain linguistic features in second-language acquisition (SLA) act as a bottleneck, limiting the progression of learners in acquiring the full grammatical system of the target language. According to this hypothesis, functional morphology is the most challenging aspect for adult L2 learners to acquire. This difficulty arises because functional morphology serves as a gateway to more complex linguistic structures and is central to linking syntax and semantics. Slabakova argues that while functional morphology is the bottleneck, other aspects of language acquisition, such as syntax and semantics, are comparatively easier to acquire because they involve structures or features that are interpretable and more directly tied to meaning.

The Critical Period Hypothesis

In 1967, Eric Lenneberg proposed the existence of a critical period (approximately 2-13 years old) for the acquisition of a first language. This has attracted much attention in the realm of second language acquisition. For instance, Newport (1990) extended the argument of critical period hypothesis by pointing to a possibility that when a learner is exposed to an L2 might also contribute to their second language acquisition. Indeed, she revealed the correlation between age of arrival and second language performance.

Cognitive Approaches to SLA

Cognitive theories explore how learners organize language knowledge. MacWhinney, Bates, and Kliegl found that speakers of different languages (English, German, and Italian) showed varying patterns in identifying the subjects of transitive sentences, highlighting the influence of L1 on L2 processing.

Connectionism models cognitive language processing using computer architectures that create associations between language elements based on their frequency of co-occurrence in input. Frequency is a significant factor in various linguistic domains of language learning. Connectionism posits that learners form mental connections between co-occurring items, extracting language rules from input through cognitive processes similar to those used in other areas of skill acquisition.

Processability theory suggests that learners restructure their L2 knowledge systems in a specific order based on their developmental stage. For example, learners acquire the correct forms for English questions through a series of consistent stages. Michael T. Ullman's declarative/procedural model explains how language information is stored, distinguishing between the storage and retrieval of facts (declarative knowledge) and the understanding of how to carry out operations (procedural knowledge).

Major Theories Influencing SLA

Three major theories have significantly influenced SLA: behaviorist, innatist, and constructivist.

Behaviorism

In the early to mid-20th century, behaviorist theories emerged, advocating for objective, empirical analysis of language acquisition. Skinner's Behaviorist theory (1957) views language as a set of structures and language acquisition as habit formation through stimulus-response repetition. Learning is considered an observable behavior acquired automatically through stimulus responses. This theory recognizes the linguistic environment but overlooks internal processes and cultural influences.

A key criticism of behaviorism is its inability to explain how learners produce original, grammatically correct sentences (Chomsky, 1976). Larsen-Freeman and Long (1991) suggest that the behaviorist model offers little explanation for SLA, except for pronunciation and rote memorization.

The Audio-Lingual Method, derived from behaviorist theories, uses language drills and objective assessments. Errors are not tolerated, as they are believed to lead to bad habits. Learning results from habit formation through imitation. The learner's first language (L1) has no place in this method due to the emphasis on imitation and recitation. Computer-assisted language learning programs like Rosetta Stone align with this method, providing input and immediate feedback.

However, audio-lingual methods have been criticized for being ineffective and unengaging. While traditional behaviorist methods can be tedious, newer computer-adaptive language learning systems based on behaviorist models can be engaging and supportive for level one language learners. Examples include Razkids.com, LearnZillion.com, Rosetta Stone, and Star Fall, which specialize in areas like phonics, grammar, and conversational English and use behaviorist methods to reinforce correct answers. These programs can supplement a communicative-based approach in the classroom.

Innatism

Noam Chomsky (1965) identified inconsistencies in the behaviorist perspective, leading to the Innatist perspective on language acquisition. Chomsky emphasizes the role of cognition in language development, suggesting that cognitive faculties enable learners to produce unlimited sentences with limited grammatical rules. This is referred to as language competence, which differs from performance.

The Universal Grammar (UG) hypothesis views SLA as an innate human capability. It posits that all humans are biologically endowed with a language faculty, the language acquisition device (LAD), responsible for language development. UG theory suggests that environmental input is insufficient to account for language acquisition. Mitchell and Myles (2004) state that the Universal Grammar approach is only interested in the learner as a processor of a mind that contains language.

According to Innatists, there is a critical period in early childhood when the brain is specifically predisposed to language acquisition. The Critical Period Hypothesis (CPH) states that the early years are crucial for acquiring a first language if adequate stimuli are present. For second language acquisition, the ideal learning time is between six and eleven years old (Lightbrown & Spada, 2006). According to CPH, if language input does not occur during this time, full command of the second language may not be attained. Research corroborates CPH, showing that learners immersed in the target language at an early age can achieve native-like proficiency in grammar and pronunciation (Johnson & Newport, 1989).

However, if native-like proficiency is not the primary goal, learners can be successful at any age. Research suggests that adolescent learners may have advanced cognitive skills that allow them to understand language forms and grammar better than younger learners (Lightbrown et al., 2006). Moreover, factors such as motivation, aptitude, investment, and opportunities to learn and practice the target language contribute to language learning ability.

Instrumental and integrative motivation theories also challenge the CPH theory (Gardner &Lambert, 1972). Instrumental language learning motivates students to learn for specific reasons, such as college or a job. Integrative learning motivates learners to acquire the language to be part of a community. A meaningful connection between a community and one's identity can increase investment in language learning (Pierce, 1995), regardless of age. Aptitude also plays a role in language learning, with some students possessing a natural proclivity for language learning that influences their rate of acquisition.

Stephen Krashen, influenced by innatism, developed the Monitor Model, which includes five hypotheses: the acquisition-learning hypothesis, the monitor hypothesis, the natural order hypothesis, the input hypothesis, and the affective filter hypothesis. Krashen emphasizes that language acquisition is an innate subconscious process. Effective teaching does not focus on explicit grammar rules or conscious learning. Language students need comprehensible input (i+1) to activate the language acquisition device (LAD) and acquire language. Comprehensible input is language that can be understood by the learner and should be slightly beyond their current ability. Teachers can make input comprehensible through drama, visuals, gestures, and repetitions. Experiential, hands-on activities make input comprehensible (Genesee, 1994).

Designing a syllabus using Krashen’s theories specifically takes the needs of the students in consideration. Criticisms of Krashen’s theories include questions about the validity of the Acquisition vs. learning hypothesis (Lydia White, 1987) and whether the five theories can be empirically tested (Lightbrown & Spada, 2006). Despite these criticisms, research shows that language students can make progress by receiving comprehensible input alone without direct instruction. However, some students may reach a plateau without direct instruction (Lightbrown & Spada, 2006).

Constructivist and Sociocultural Views

Jean Piaget explains that all learning, including knowledge acquisition, stems from a student’s active involvement in knowledge construction. Similarly, Vygotsky views learning as a result of knowledge construction. However, Vygotsky believed social interactions and culture had a greater influence on linguistic and cognitive faculties, leading to Sociocultural theory.

Sociocultural theory explains that learning is a semiotic process where participation in socially mediated activities is essential. Students’ understanding of language structure and function develops by using the language in social settings. Vygotsky’s theory suggests that L2 students should be taught according to their Zone of Proximal Development (ZPD). The zone of proximal development refers to the distance between what children can do by themselves, and what they can achieve with assistance from a mentor. Scaffolded teaching and learning methods in turn use the ZDP to provide support for students. The teacher provides scaffolds to support the students learning to create academic growth. Scaffolding is similar to Krashen’s comprehensible input (i+1) as it uses what the child already knows to introduce new knowledge or skills. The teacher should engage the student in a task that is just slightly more difficult that what the student can do on their own. The teacher then helps the student progress through the ZDP to attain new levels of achievement. Scaffolding can take many different forms in the classroom such as models, cues, prompts, hints, partial solutions, think-aloud modeling and direct instruction (Hartman, 2002). For language learners, semi-controlled activities that include a prompt with some freedom when discussing literature can be effective. For instance, teaching students how to participate in whole group discussions by using phrases like, "I made a text-to-self connection when…”, or “I made an inference when…”. Each day focusing on mastering a different prompt and within a few weeks students no longer need to be prompted. Students can engage in whole group or small group to successfully discuss literature on their own. Slowly taking away the prompt is an important part of students achieving mastery on their own.

Communicative Competence

The communicative approach to second language acquisition begins with the premise that language is communication, and the goal of language acquisition is to communicate. Hymes (1972) advocates for a constructivist, communicative approach to language learning, claiming that the old innatist model does not take into account any sociocultural features of language.

Hymes (1972) developed the theory of communicative competence, distinguishing between linguistic competence and communicative competence. In previous years, linguistic competence meant the ability to create well-formed sentences (Chomsky, 1965). Hymes' view of communicative competence ascribes competences to knowing what to say, when to say it, and how to say it. Communicative competence highlights the difference between knowledge about language and knowledge that enables a person to communicate functionally and interactively. Halliday (1973) explains that the interpersonal aspect of the elements of the dialogue help to reinforce the sense that speakers are working together to negotiate meaning when they engage in conversation. Swain and Canale (1980) expanded communicative competence to include four major competence components: grammatical, sociolinguistic, strategic, and discourse. Grammatical competence, meaning grammatical capacity, “refers to what Chomsky calls linguistic competence and what Hymes calls formally possible” (Richards & Rogers, 2001, p. 160). Sociolinguistic competence refers to communication within an interactive social setting. Discourse competence refers to how a part of the discourse contributes to the whole discourse. Finally, strategic competence involves the strategies learners use to overcome communication breakdowns and enhance their understanding.

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