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Critical Periods in Speech Perception: New Directions Janet F. Werker 1 , 3 and Takao K. Hensch 2 , 3 1 Department of Psychology, University of British Columbia, Vancouver British Columbia V6T 1Z4, Canada; email: [email protected] 2 Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138; email: [email protected] 3 Canadian Institute for Advanced Research, Toronto Ontario M5G 1Z8, Canada Annu. Rev. Psychol. 2015. 66:173–96 First published online as a Review in Advance on September 17, 2014 The Annual Review of Psychology is online at psych.annualreviews.org This article’s doi: 10.1146/annurev-psych-010814-015104 Copyright c 2015 by Annual Reviews. All rights reserved Keywords infancy, language acquisition, attention, GABA, parvalbumin, perineuronal net Abstract A continuing debate in language acquisition research is whether there are critical periods (CPs) in development during which the system is most re- sponsive to environmental input. Recent advances in neurobiology provide a mechanistic explanation of CPs, with the balance between excitatory and inhibitory processes establishing the onset and molecular brakes establishing the offset of windows of plasticity. In this article, we review the literature on human 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 paradigmatic examples testing CP models in human subjects. We conclude with a discus- sion of how a mechanistic understanding of CP processes changes the nature of the debate: The question no longer is, “Are there CPs?” but rather what processes open them, keep them open, close them, and allow them to be reopened. 173 Annu. Rev. Psychol. 2015.66:173-196. Downloaded from Access provided by Harvard University on 06/09/15. For personal use only.
Contents INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 DEFINITION OF CRITICAL PERIODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 Conceptual Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 Biological Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 CRITICAL PERIODS IN SPEECH PERCEPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Phoneme Perception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 Audiovisual Matching and Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 PROBING LANGUAGE CRITICAL PERIODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Shifting Onset Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Early Enrichment: Bilingual Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 Early Deprivation: Deafness and Cochlear Implants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 THE LASTING IMPACT OF CRITICAL PERIOD DEVELOPMENT . . . . . . . . . . . 186 Later Language Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Perceptual Savings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 REOPENING CRITICAL PERIODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 CONCLUSIONS AND FUTURE DIRECTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 INTRODUCTION The ability to acquire human language is one of the quintessential characteristics of our species. Al- though many animals have communication systems, only human language allows the construction of an infinite number of new sentences not only to share needs and desires, but also to comment on the past and the future, to consider new possibilities, and to construct poetry and narrative.

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