Janet Werker: How Babies Begin Learning Their Native Language co.9

Overview

• Janet Werker received the APS William James Research Award for landmark infancy research.
• Talk focus: how infants begin learning native languages via perceptual development.
• Time span of research discussed: prenatal (in utero) to ~2 years, with bilingual and preterm considerations.

Key Findings About Infant Language Perception

• Newborns show differential brain responsiveness to speech versus non-speech.
• Fetuses hear and begin learning rhythmic properties of maternal speech before birth.
• Infants are born able to discriminate many phonetic contrasts across world languages.
• Perceptual attunement (narrowing) occurs in the first year: broad discrimination narrows toward native-language contrasts by ~10–12 months.
• Early perceptual tuning supports later word learning and vocabulary growth.

Important Concepts And Mechanisms

• Perceptual Attunement / Narrowing
  • Infants initially discriminate non-native contrasts; ability declines for unattended contrasts.
  • Native-language expertise emerges by 12 months; some sensitivities persist longer.
• Distributional (Statistical) Learning
  • Exposure to bimodal distributions (two peaks) of sounds facilitates forming two categories.
  • Effective primarily at 6–8 months; much harder after 10–12 months.
• Word-Referent Mapping
  • Consistent pairing of distinct sounds with distinct objects helps discrimination around 9–10 months.
  • Mapping cues that signal "this is about words" improve learning of tone or stress contrasts.
• Critical / Sensitive Periods
  • Plasticity windows are gated by molecular mechanisms (inhibition/excitation balance).
  • Maturational timing and experience both influence opening/closing of these windows.
  • Preterm infants: earlier exposure to broadcast speech does not shift timing of attunement; maturation gates sensitivity.
• Pharmacological and Maternal Factors
  • Prenatal exposure to SSRIs (antidepressants) can accelerate loss of non-native discrimination.
  • Maternal depression without pharmacological treatment can delay narrowing.
  • Both acceleration and delay may have downstream consequences for word learning and development.

Multi-Sensory And Motor Contributions

• Infants use audiovisual speech cues; visual-only cues can distinguish languages at 4–6 months.
• McGurk-like effects and bimodal matching occur in infancy; visual influence declines for non-native distinctions by ~10 months unless bilingual exposure.
• Oral-motor (articulatory) influences:
  • Preventing specific tongue or lip movements disrupts infants' discrimination of related speech contrasts.
  • Suggests early speech representations are multisensory and include motor/articulatory components.
• Multisensory development models:
  • Traditional: modalities develop independently, integrate later.
  • Alternative (Werker’s view & others): sequential scaffolding — early motor/oral templates facilitate later auditory and visual tuning.

Evidence Linking Perception To Later Language Outcomes

• Better discrimination of native contrasts (and reduced sensitivity to non-native contrasts) in the first year correlates with larger vocabularies at age two.
• Phonological categories formed in infancy guide mapping of words to meanings at 18–20 months (e.g., Dutch vowel length contrast used by Dutch toddlers only).
• Delays or atypical timing (e.g., due to hearing loss) can hinder phonological category formation and subsequent word learning; early cochlear implantation mitigates some delays.

Bilingual And Cultural Context Effects

• Bilingual infants follow similar perceptual timelines but retain sensitivity to both languages longer.
• Visual language cues:
  • By 11 months, Vancouver infants associate ethnicity with likely language (e.g., ethnic Chinese faces → Chinese speech).
  • Bilingual infants discriminate language-specific contrasts better when preceded by a face matching the cultural/ethnic source of that language.
• Cultural/ethnic cues can help bilingual infants separate and learn each language in complex input environments.

Methods Mentioned

• Neuroimaging and newborn brain activation studies (functional specialization present near birth).
• Behavioral paradigms:
  • Sucking paradigm (fetal/newborn preference for familiar language).
  • Conditioned head-turn (infant discrimination).
  • Distributional familiarization (bimodal vs. unimodal sound exposure).
  • Word-object mapping (switch paradigm).
  • Fetal heart rate (in utero discrimination).
  • Oral perturbation (placing teether to restrict tongue/lip movement).
  • Silent visual-only speech videos (language discrimination by sight).

Key Terms And Definitions

• Phonetic Discrimination: ability to distinguish speech sound contrasts (e.g., dental vs retroflex).
• Perceptual Attunement: narrowing of perceptual sensitivity toward native-language sounds.
• Distributional Learning: learning categories from statistical distributions of stimuli.
• Critical Period: developmental window of heightened sensitivity to environmental input.
• McGurk Effect: visual information alters perceived speech sound in adults and infants.
• Parvalbumin Cells: interneurons involved in gating plasticity via inhibition/excitation balance.

Implications And Applications

• Early perceptual tuning is foundational for word learning and later language development.
• Timing of plasticity matters: both premature acceleration and delays can be problematic.
• Clinical relevance for:
  • Children with hearing loss (importance of early cochlear implants).
  • Babies with oral-motor or visual impairments.
  • Considerations around prenatal SSRI exposure and maternal mental health interventions.
• Bilingual environments: infants use multiple cues (auditory, visual, cultural) to separate languages.

Action Items / Next Steps (If Applicable)

• Longitudinal follow-up: continue tracking children with prenatal SSRI exposure and maternal depression to assess long-term outcomes.
• Further research:
  • Mechanisms linking motor/oral development and auditory speech perception.
  • How cultural cues interact with bilingual acquisition across different communities.
  • Interventions to support infants with delayed or atypical perceptual tuning.
• Clinical translation: refine guidelines for early detection and intervention (hearing, motor, visual) to support phonological category formation.

Summary Table: Developmental Milestones And Influences