Language Development in the First Two Years — Milestones, Mechanisms, and Theories

Milestones in the first two years

  • 0–2 months: Reflexive communication (cries, facial expressions).
  • 2–6 months: Meaningful noises (cooing, fussing, laughing).
  • 6–10 months: Babbling with consonant–vowel syllables.
  • 10–12 months: Comprehension of simple words; first signs for deaf babies; pointing begins.
  • 12 months: First spoken words in native language.
  • 13–18 months: Slow vocabulary growth (up to ∼\sim50 words); naming explosion starts.
  • 18–21 months: Rapid growth (∼\simthree+ words/day); first two-word sentence at ∼\sim21 months.
  • 24 months: Multiword sentences; half of utterances are two words or longer.
  • Note: Sequence is universal; timing varies across cultures.

Early listening and infant-directed speech

  • Infants prefer voices to other sounds; attuned to speech, alliteration, rhymes, and varied pitch.
  • Caregivers use child-directed speech (Motherese): higher pitch, simpler words, repetition, exaggerated emotion, promoting attention and learning.

Babbling, gestures, and social cues

  • Babbling is universal and includes cries, coos, then syllables (mama, papa, dada).
  • Deaf babies babble; sign language is crucial for their early communication.
  • Gestures (e.g., pointing) emerge around 12 months, predict later speech, and are communicative (responding to pointing is essential).

Word formation, holophrases, and grammar emergence

  • ∼\sim12 months: First words, understood by caregivers first.
  • ∼\sim18 months: Naming explosion (many nouns).
  • 18–24 months: Grammar appears; two-word combinations (e.g., mommy read; baby cry).
  • By 24 months: Grammar effects clearer; MLU (Mean Length of Utterance) rises with morphology and syntax.
  • Holophrases: Single words expressing broader meanings (with gestures, tone, context).
  • Examples: Simple two-word orders vary by language (e.g., English SVO).

Measuring progress: Mean Length of Utterance (MLU)

  • MLU tracks grammatical development:
    MLU=total morphemestotal utterances\text{MLU} = \frac{\text{total morphemes}}{\text{total utterances}}
  • Higher MLU indicates more advanced syntax and morphology.

Theories of language learning (three schools)

  1. Behaviorism (Skinner): Infants are taught via reinforcement and association. (Limits: doesn't fully explain rapid acquisition).
  2. Social-interaction / sociocultural (Tomasello): Language emerges from social needs, joint attention, imitation, and cultural context. (Cautions against passive video learning).
  3. Nativist / language-internal constraints (Chomsky, Pinker): Innate Language Acquisition Device (LAD) and Universal Grammar; brain expects to hear language.
  • Contemporary view: Language learning results from multiple interacting factors (behavioral, social, biological) with cascades of development.

Neuroscience perspective

  • Language involves multiple brain regions beyond Wernicke’s and Broca’s areas, with numerous genes and neural networks contributing.
  • Sign language engages the same language networks; development involves neural changes and experience-dependent pruning.

Key takeaways for exam review

  • Language development in the first two years follows a universal sequence.
  • Milestones include reflexive communication, babbling, gesture, first words, naming explosion, two-word, then multiword sentences.
  • Child-directed speech, caregiver responsiveness, pointing, and gaze are crucial.
  • Babbling and gestures predict later language.
  • Grammar emerges with increasing MLU and more complex syntax.
  • Language acquisition is explained by behaviorist, sociocultural, and nativist theories, with a contemporary hybrid view.
  • Neuroscience highlights distributed brain networks, genes, and plasticity in language learning.