Week 12 - Infant directed speech

Brain development for language

development of auditory system ~ 20 weeks gestation

2 hypothesis on brain development and language

1. Equipotentiality hypothesis

2. Invariance hypothesis

1. Equipotentiality Hypothesis

No hemispheric specialization for language at birth, it comes with time

• specialization of left hemisphere comes later

• as the infant develops and is more exposed to language the left hemisphere is able to develop

• language it lateralized to the left side of the brain

2. Invariance Hypothesis

• hemispheric specialization for language at birth

• comparable left hemisphere organization to adults

• the left hemisphere is already specialized this right from the start

Evidence for the Invariance hypothesis

• Left hemisphere >(more activated than) Right hemisphere when you infants hear speech sounds

• Patients with aphasia (when language is impaired) tend to have left-hemispheric damage over right-hemisphere → but there is plasticity for acquiring language (new neural pathways will be supported to direct language elsewhere for production

• infants open right side of mouth more when babbling, but not when making other vocalizations (language lateralized to left side).

  • Contralateral processing - opposite side of the brain sends message to the other side of the body - if the right side opens more, the left side is controlling that

Critical language acquisition phase

• developing infant, infant needs to be exposed to language in order to acquire it

• in order to find the critical period for language acquisition you need to find a way to test it

ex. 2 year, 5 year, 7 year old learn a new language and see which group learns best, but this is challenging because the child may have passed through the critical period already

critical time period: case study

• no language exposure till age 13

• gain some semantics (map words to meaning), but don’t acquire full syntax (grammar)

• challenge: there can be developmental delays through abuse, etc.

Learning Language later in life (hoff 2008)

1. sign language- early learners have better grammar than late learners. Some children aren’t exposed to sign language till later, learning sign language has shown to lead to better grammar (full syntax)

2. second language - younger learners are more proficient

Babbling

the production of sounds that involves phonemes spanning human language

Stages of babbling

1. Quasi-resonant vocalization (QRV) → sounds not coming through mouth cavity, whiny vocalizations

2. Fully-resonant vowel (FRV) → mostly vowel sounds, no real consonant sounds yet (3-4 months)

3. Marginal-syllable: consonant and vowel sounds (4-8 months)

4. Canonical syllable → ‘typical’ syllable sequences for a language (9 months)

Gestures

• gestures can be a pre-cursor to language

• infants use gestures to communicate what they want when they can’t yet speak → pointing, eye gaze, etc.

• iconic gestures - clearly map to the meaning of the object

• symbolic gestures - combined with language to provide meaning to the object

3 key behavioral methods to measure speech perception in infants

1. Looking time preference procedure

2. head-turn procedure

3. habituation procedure

Method 1: Looking time preference procedure

• what do infants like?

• if infants look longer in one direction then infant must prefer that sound

• in the example they turned more to the side that presents the motherese (infant directed speech) rather than presenting adult directed speech

Method 2: Head turn procedure

• do infants detect a change in sound?

• if infants turn head when a change in the auditory stimulus happens, then they detected the change

• turn head toward one direction they are rewarded with something

Method 3: Habituation procedure

• do infants detect novelty changes in sound?

• if infants look longer at novel sounds then they detect a change

• repetitive sounds = decrease looking time

• new sounds = new exciting things = increase looking time

What is infant directed speech?

• the tendency to alter how we communicate with infants

• modulate speech sounds in specific ways when interacting with infants

  • hyper articulationID of vowels

  • more variable speech pattern (pitch)

  • higher frequency

  • slower speech/longer pauses

IDS changes across development

• IDS persists across first year of life

• as infants get older people change how they speak to them to allow them to properly understand

Does IDS affect language acquisition

Study 1: Exaggerate different sounds

Study 2: clarity of important sounds

Study 1: exaggerate different sounds - does caregiver speech variability relate to infants’ detection of different S sounds?

• YES!

• creating differences in speech sounds may facilitate speech perception

• novel sounds with greater distinction generate more interest than the habituate sounds

Study 2: does clarity of important sounds affect word recognition?

• hyper articulation creates longer gaze on the correct word

• more vowel hyper articulation (exaggeration) = better word recognition

Does everyone use IDS? are there cultural difference?

• not all cultures speak to infants the same way

• we can recognize differing IDS in different cultures because of the tone, pitch and speed of the sounds