The Critical Period Hypothesis in Second Language Acquisition: A Statistical Critique and a Reanalysis

Jan Vanhove,Stephanie Ann White

doi:10.1371/journal.pone.0069172

Abstract

In second language acquisition research, the critical period hypothesis (cph) holds that the function between learners' age and their susceptibility to second language input is non-linear. This paper revisits the indistinctness found in the literature with regard to this hypothesis's scope and predictions. Even when its scope is clearly delineated and its predictions are spelt out, however, empirical studies–with few exceptions–use analytical (statistical) tools that are irrelevant with respect to the predictions made. This paper discusses statistical fallacies common in cph research and illustrates an alternative analytical method (piecewise regression) by means of a reanalysis of two datasets from a 2010 paper purporting to have found cross-linguistic evidence in favour of the cph. This reanalysis reveals that the specific age patterns predicted by the cph are not cross-linguistically robust. Applying the principle of parsimony, it is concluded that age patterns in second language acquisition are not governed by a critical period. To conclude, this paper highlights the role of confirmation bias in the scientific enterprise and appeals to second language acquisition researchers to reanalyse their old datasets using the methods discussed in this paper. The data and R commands that were used for the reanalysis are provided as supplementary materials.

Highlights

In the long term and in immersion contexts, second-language (L2) learners starting acquisition early in life – and staying exposed to input and learning over several years or decades – undisputedly tend to outperform later learners
The age–susceptibility function is hypothesised to be non-linear. Moving beyond this general version, we find that the critical period hypothesis (CPH) is conceptualised in a multitude of ways [4]
Discussions about the impact of empirical findings on the tenability of the CPH generally revolve around the reliability of the data gathered (e.g. [5,14,22,52,67,68]) and such methodological critiques are highly desirable

Summary

Introduction

In the long term and in immersion contexts, second-language (L2) learners starting acquisition early in life – and staying exposed to input and learning over several years or decades – undisputedly tend to outperform later learners. Derived from biology, the CP concept was famously introduced into the field of language acquisition by Penfield and Roberts in 1959 [1] and was refined by Lenneberg eight years later [2]. Lenneberg argued that language acquisition needed to take place between age two and puberty – a period which he believed to coincide with the lateralisation process of the brain. 176] in immersion contexts and does not preclude the possibility of learning a foreign language after puberty, albeit with much conscious effort and typically less success The critical period concept was concerned with the implicit ‘‘automatic acquisition’’ [2, p. 176] in immersion contexts and does not preclude the possibility of learning a foreign language after puberty, albeit with much conscious effort and typically less success

Results

Discussion

Conclusion