Single-system and dual-system hypotheses in multilingualism

Single-System and Dual-System Hypotheses in Multilingualism

Multilingualism, the ability to speak and understand multiple languages, has led researchers to explore how these languages are represented and processed in the brain. Two prominent hypotheses that explain this are the single-system and dual-system hypotheses. These hypotheses offer different views on whether multilingual individuals have separate or integrated language systems for each language they speak.

Single-System Hypothesis

The single-system hypothesis posits that multilingual individuals have a unified language system. According to this view, all the languages a person knows are stored and processed within the same cognitive and neural network. This hypothesis suggests that there is significant overlap in the neural representations and cognitive processes used for all languages spoken by an individual.

Key Points of the Single-System Hypothesis:

Shared Representations: The languages share the same mental lexicon and grammatical rules to a large extent.
Interconnected Processing: Cognitive processes involved in using one language can influence and support the use of another language.
Language Interaction: Bilinguals and multilinguals often show cross-linguistic influence, where knowledge of one language affects performance in another.

Evidence Supporting the Single-System Hypothesis:

Code-Switching: The seamless switching between languages in conversation suggests an integrated system.
Neuroimaging Studies: Some studies show overlapping brain regions activated during the processing of multiple languages.
Transfer Effects: Learning a new language can enhance cognitive abilities that are beneficial across all known languages, indicating shared processing mechanisms.

Dual-System Hypothesis

The dual-system hypothesis, on the other hand, argues that multilingual individuals maintain separate language systems. According to this view, each language is stored and processed independently, with minimal overlap between the neural and cognitive mechanisms for each language.

Key Points of the Dual-System Hypothesis:

Distinct Representations: Each language has its own lexicon and grammatical rules stored separately.
Independent Processing: Cognitive processes for one language operate independently from those for another language.
Minimal Interaction: Knowledge and use of one language have limited influence on the other languages known by the individual.

Evidence Supporting the Dual-System Hypothesis:

Selective Aphasia: Some bilingual individuals with brain damage may lose the ability to speak one language while retaining the other, suggesting separate systems.
Neuroimaging Studies: Certain studies show distinct brain regions activated for different languages, especially if the languages were learned at different times or are typologically different.
Error Patterns: Bilinguals often make language-specific errors, which could indicate separate processing systems.

Integration of Both Hypotheses

Modern research suggests that the reality of multilingual language processing might be more complex than either hypothesis alone can explain. It is likely that aspects of both hypotheses are true to varying degrees, depending on several factors such as:

Age of Acquisition: Early bilinguals are more likely to show integrated language systems, while late bilinguals might exhibit more separated systems.
Language Proficiency: Higher proficiency in both languages may lead to more integrated systems.
Language Similarity: Typologically similar languages might be processed more in an integrated manner than very different languages.

Conclusion

The single-system and dual-system hypotheses offer valuable insights into how multiple languages are represented and processed in the brain of multilingual individuals. While the single-system hypothesis emphasizes shared cognitive and neural resources, the dual-system hypothesis highlights separate and independent language systems. Current understanding suggests a more nuanced perspective, with the degree of integration or separation influenced by factors such as age of acquisition, language proficiency, and language similarity. Further research, especially with advanced neuroimaging techniques, continues to shed light on the complexities of multilingual language processing.