Critical Periods in SpeechPerception: New DirectionsJanet F. Werker1,3and Takao K. Hensch2,31Department of Psychology, University of British Columbia, Vancouver British Columbia V6T1Z4, Canada; email: [email protected]2Department of Molecular and Cellular Biology, Harvard University, Cambridge,Massachusetts 02138; email: [email protected]3Canadian Institute for Advanced Research, Toronto Ontario M5G 1Z8, CanadaAnnu. Rev. Psychol. 2015. 66:173–96First published online as a Review in Advance onSeptember 17, 2014TheAnnual Review of Psychologyis online atpsych.annualreviews.orgThis article’s doi:10.1146/annurev-psych-010814-015104Copyright c 2015 by Annual Reviews.All rights reservedKeywordsinfancy, language acquisition, attention, GABA, parvalbumin, perineuronalnetAbstractA continuing debate in language acquisition research is whether there arecritical periods (CPs) in development during which the system is most re-sponsive to environmental input. Recent advances in neurobiology providea mechanistic explanation of CPs, with the balance between excitatory andinhibitory processes establishing the onset and molecular brakes establishingthe offset of windows of plasticity. In this article, we review the literature onhuman speech perception development within the context of this CP model,highlighting research that reveals the interplay of maturational and experien-tial inﬂuences at key junctures in development and presenting paradigmaticexamples testing CP models in human subjects. We conclude with a discus-sion of how a mechanistic understanding of CP processes changes the natureof the debate: The question no longer is, “Are there CPs?” but rather whatprocesses open them, keep them open, close them, and allow them to bereopened.173Annu. Rev. Psychol. 2015.66:173-196. Downloaded from Access provided by Harvard University on 06/09/15. For personal use only.