Critical Periods in Speech Perception: New Directions

Abstract

A continuing debate in language acquisition research is whether there are critical periods (CPs) in development during which the system is most responsive 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 experiential influences at key junctures in development and presenting paradigmatic examples testing CP models in human subjects. We conclude with a discussion 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.

Behavioral and Neural Foundations of Multisensory Face-Voice Perception in Infancy

“…Second, starting around 6-months of age when attention is more flexible for various amodal and modality specific properties, infants can learn various arbitrary features (i.e., the sound of a particular voice and the visual appearance of a particular face) associated with a particular face-voice pairing. Neural and behavioral signatures of multimodal processing comparing younger to older infants suggest Intersensory Perception 28 that this development may be coupled with a tuning to the particular combinations of races and species and languages to which they are exposed (Vogel et al, 2012;Scott et al, 2007or Werker & Hensch, 2015.…”

“…Instead, they showed latency differences on earlier perceptual processing (P400) of faces by congruency but only for more familiar Caucasian faces. The authors took these results as evidence of narrowing in intersensory perception that mirrors the developmental time course and nature of experienceIntersensory Perception 25 dependent narrowing in unimodal auditory and visual perception for voices and faces (see Scott, Pascalis, & Nelson, 2007or Werker & Hensch, 2015 for reviews). Interestingly, there also appeared to be a shift in the brain systems involved in interensory processing over development.…”

“…These aspects of the neural response correspond to some of the attentional preferences Intersensory Perception 27 and memory advantages predicted by the intersensory redundancy hypothesis and observed behaviorally in infants of the same age for bimodal redundant face-voice stimuli compared to unimodal face, unimodal voice, or bimodal non-redudant face-voice stimuli (Bahrick, 2000;2001Lewkowicz, 2000; 2010 for reviews). Second, some preliminary results suggest that brain indices of attention, perception, and memory to different race faces and emotion pairings (Vogel et al, 2012) parallel perceptual narrowing effects seen in behavior for race and voice unimodally (see Scott et al, 2007or Werker & Hensch, 2015.…”

Can infants learn phonology in the lab? A meta-analytic answer

“…An overwhelming body of evidence suggests that attunement to the ambient language's phonology begins in infancy (Werker & Hensch, 2015), raising the question of what mechanisms may begin to operate at such an early age. Given that infants' lexicon is highly constrained, a mainstream assumption posits that infants may begin to learn their language's sound system by applying simple statistical mechanisms directly onto the spoken signal they hear.…”

Effects of enriched auditory experience on infants’ speech perception during the first year of life

“…In songbirds, learning their species-typical song depends on experience during a critical temporal window; presentation of conspecific song during that time is essential for normal development (Konishi 1985;Marler 1970). A recent theoretical paper (Werker and Hensch 2015) discusses the nature of the ''critical'' periods, especially the biological factors that ''open'' and ''close'' them. Here, we review work from our laboratory that focuses on one specific time period for human infants' learning; namely, the ''sensitive period'' for phonetic learning and the experiential factors that may influence this learning process.…”