Life history theory and the explore-exploit dilemma illuminate sensitive-period effects in second language learning
Date
2023-06-03
DOI
Authors
Caldwell-Harris, Catherine
Version
Other
OA Version
Citation
C. Caldwell-Harris. 2023. "Life history theory and the explore-exploit dilemma illuminate sensitive-period effects in second language learning."
Abstract
The difficulty of learning languages in adulthood compared to childhood suggests that language is constrained by a maturationally-based sensitive period. But no genetic mechanisms for limiting language learning have been identified despite decades of investigation. The teen years are supposedly post-sensitive period, but are now recognized as a time when the brain is highly plastic and approaching its cognitive peak. Even if genetic mechanisms exist for muting second language acquisition (SLA), one must still explain why a domain-specific reduction in language learning ability would have been evolutionarily adaptive.
Theoretical proposal. A new maturational explanation of age effects in SLA is presented, rooted in life history theory. Life history theory is a framework for understanding how organisms navigate resource allocation trade-offs. In contrast to the juvenile years, it is not adaptive for adults to spend hours a day processing completely novel informational structures. Learning a new language poses prohibitive opportunity costs, since that time is unavailable for pursuing adult roles including consolidating status. Practicing a foreign language positions adults in a role of diminished competence. This is experienced as tedious and unrewarding, unless incentives are in place. Such incentives include the rare situation when adults can not rely on their L1 for communication, and thus must learn the L2 for social rewards and basic survival.
Hypotheses. The resource allocation and opportunity costs account of SLA age effects is used to explain why motivation to acquire a second language declines in the late teen years and adulthood. (Note that a second language is defined as a language acquired after a first language has been mastered, which usually means after age 4 or 5.) A specific prediction is that that the age at which one can best most easily learn a second language while maintaining fluency in the home language is middle childhood and the early teen years. This view differs from the common assumption that a younger language learner is always superior to an older learner.
Method. Interviews were conducted with 80 Russian-English and Spanish-English immigrants, aged 18-56. Respondents discussed their current and childhood usage patterns and rated their language abilities. A third group of learners were 156 immigrants and heritage language learners (different L1s with L2 English). They completed a questionnaire to assess usage patterns; English grammar, morphology and vocabulary were also measured.
Results. Language use, preferences and ability varied systematically with age of arrival. Those who immigrated in early childhood reported growing up in an environment rich in the language of the new country, facilitating dominance in L2, while halting or reversing abilities in L1 (L1 attrition). Those who immigrated in the late teen years (after age 14) reported nostalgia for their L1, and sought out environments in their new country which were rich in L1, facilitating L1 maintenance.
Conclusion. Age effects in SLA reflect cognitive systems that prioritize learning from caregivers in infancy and early childhood, from peers in middle childhood, and from the larger culture in the early teen years. By adulthood, learning entirely new information is avoided in favor of consolidating and gaining status from existing knowledge systems. On this view, it is wasteful to set aside two decades spent learning a first language by retraining on a new second language. Indeed, the situation of immigration to a culture with a different language can probably be considered evolutionarily unanticipated, even though multilingualism was almost certainly common in ancestral time, given contemporary hunter-gather societies.
For convenience, the proposed maturationally-constrained learning systems have been described as stage-like, but the actual account specifies quantitative and continuous change with age. In addition, these learning stages are assumed to exhibit considerable flexibility. The teen years were likely a special time where environmental signals could incentivize investment in a new language. This as may have been the cause of good L2 learning for Russian-English interviewees who immigrated in young adulthood. Personal, family and socio-political factors can motivate young adult immigrants to stay in a knowledge acquisition mode longer, thus devoting more energy to learning L2. In rare cases, environmental contingencies can activate the knowledge acquisition system in an older immigrant, thus facilitating SLA in the 30s and beyond.