Social Development in infancy

Infant Directed Speech Characteristics

🧠 Infant-Directed Speech (IDS) 🔊 Acoustic Characteristics (How it sounds)

IDS is:

• Higher pitch → “baby voice”

• Slower tempo → easier to process

• Exaggerated pitch changes (frequency modulation)
  👉 big ups and downs in voice

• Exaggerated loud/soft differences (amplitude modulation)
  👉 loud parts are louder, soft parts are softer

• Simplified language
  👉 fewer words, shorter sentences, lots of repetition

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🌍 Universality

• Found across many languages and cultures

• Considered nearly universal

👉 Suggests IDS is a natural way humans communicate with infants

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🎵 Cross-Cultural Pitch Patterns 🚫 Prohibition Contours

• Sharp, abrupt pitch changes

• Sounds like: “NO!”
  👉 Signals warning or stopping

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❤ Comfort Contours

• Smooth, gentle pitch changes

• Gradual rises and falls
  👉 Helps calm infants (reduces arousal)

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🎉 Arousing Contours

• Large increases in pitch

• Highly exaggerated
  👉 Used to highlight important words
  👉 Grabs attention and excites the infant

Function of Infant-Directed Speech (IDS)

🧠 Function of Infant-Directed Speech (IDS)

IDS happens in two important contexts:

• Babies are born with a preference for human/maternal voices

• Babies have a slowly developing visual system in the first year

👉 Because of this, IDS helps infants:

• Organize their attention to important things

• Especially while their vision is still developing

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🎯 Main Function

IDS helps solve a key problem for infants:

👉 How do I know what words refer to?

IDS helps babies:

• Focus on relevant objects

• Map words onto objects in their environment

👉 In other words, IDS makes it easier for babies to learn:

• What to learn

• Where to look

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🔍 Attention Function

IDS:

• Captures attention

• Attracts attention

• Maintains attention

👉 It helps babies focus on important parts of a complex environment

IDS Experiment

🧪 Key Experiment (More Detailed but Clear)

Researchers studied 4-month-old infants to see how IDS affects attention

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Step 1: Habituation

Babies were shown a checkerboard pattern for 10-second trials

👉 At first:

• Babies looked at it

👉 Over time:

• They got bored

• Looked less and less

➡ This is called habituation

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Step 2: Add Sound (“Round and around”)

After babies got bored, researchers added speech while showing the SAME checkerboard

They tested two types of speech:

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Condition 1: Adult-Directed Speech

• Normal adult voice

• Babies looked a little longer

👉 But:

• The increase was NOT significant

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Condition 2: Infant-Directed Speech (IDS)

• High pitch

• Exaggerated tone

• “Baby voice”

👉 Babies looked much longer at the checkerboard

➡ This was a significant increase in attention

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💡 What This Shows

IDS caused dishabituation

👉 Meaning:

• Something old and boring became interesting again

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🎯 Key Idea

IDS doesn’t just attract attention — it can:
👉 Bring attention BACK to something babies already got bored of

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🧠 Simple Explanation

• Baby gets bored of object

• Add IDS →
  👉 Baby thinks: “Wait, this is interesting again”

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Infant-directed motion

Infant-Directed Motion (IDM) + IDS & Word Learning 🔑 Core Idea

Caregivers don’t just use infant-directed speech (IDS) — they also use infant-directed motion (IDM)

👉 IDM = moving objects in:

• Exaggerated ways

• Synchronized with speech

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🔗 What is Infant-Directed Motion (IDM)?

Research shows:

• Caregivers move objects more dramatically when showing them to infants

• Movements are timed with speech

👉 Example:
“Look at the BALL!” → object moves at the same time

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🌐 Why IDM Matters (Big Concept)

This creates intersensory redundancy

👉 The same information is given through:

• Auditory input (speech)

• Visual input (motion)

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🎯 Function of IDM

IDM helps infants:

• Direct their attention to the correct object

• Solve the problem:
  👉 “What is this word referring to?”

• Strengthen word–object associations

👉 Especially important for younger infants whose attention is still developing

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🧪 IDS + IDM Experiment (Word Learning) 🎯 Goal

Test whether:
👉 IDS and IDM help infants learn new words

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🧪 Study Design Participants

• 13-month-olds

• 15-month-olds

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Stimuli

• Novel objects
  👉 prevents prior knowledge

• Fake words
  👉 sound like English but have no meaning

• Controlled for:
  👉 object preference

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🔁 Manipulations 1. Speech Type

• IDS (baby talk)

• ADS (adult speech)

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2. Motion

• No motion

• Synchronized motion (IDM)

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🧩 4 Conditions

1. IDS + no motion

2. IDS + motion

3. ADS + no motion

4. ADS + motion

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🧠 Test Phase (24 hours later)

• Infants shown both objects

• Asked to choose one (e.g., “Give me the ___”)

👉 Measure:
Did the infant correctly remember the word–object pairing?

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👶 Results 13-Month-Olds

👉 Best performance: IDS + motion

• Needed BOTH cues

• Motion helped guide attention

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💡 Interpretation

Younger infants:

• Don’t automatically know where to look

• Need visual + auditory cues together

👉 IDM acts as a signal:
“This is the object the word refers to”

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15-Month-Olds

👉 Best performance: IDS alone

• Motion did NOT add benefit

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💡 Interpretation

Older infants:

• Better attention control

• Already understand:
  👉 “When I hear IDS, I should look at the object”

👉 No longer need intersensory redundancy

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🔥 Key Developmental Shift

• 13 months → rely on intersensory redundancy (IDS + IDM)

• 15 months → rely on speech alone

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🎯 Big Theoretical Takeaway

This study shows:

👉 Learning depends on multiple cues early in development

👉 Over time, infants become:

• More efficient

• Less dependent on extra support

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🧠 Why This Matters

• Demonstrates developmental change in attention and learning

• Shows how social interaction (speech + motion) supports learning

• Explains how infants solve the problem of:
  👉 “What does this word refer to?”

Influence of IDS on Early Word Learning

🧠 Influence of IDS on Early Word Learning

Researchers wanted to test:
👉 Does infant-directed speech (IDS) actually help babies learn new words?

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They studied 13- and 15-month-old infants by:

• Showing them new (novel) objects

• Giving them made-up words to label those objects

👉 The fake words sounded like English, but had no meaning
👉 This made sure babies weren’t using prior knowledge

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They also changed how the objects were presented

Because in real life:
👉 Parents don’t just talk differently —
👉 They also move objects in sync with their speech

This is called:

• Infant-directed motion

• Intersensory redundancy (multiple cues together: sound + movement)

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🧪 What They Manipulated

There were 2 things changing:

1. Type of Speech

• IDS (baby talk)

• ADS (normal adult speech)

2. Motion

• No movement

• Synchronized movement (object moves with speech)

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🧩 4 Conditions

1. IDS + no motion

2. IDS + motion

3. ADS + no motion

4. ADS + motion

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🧠 Memory Test (24 hours later)

Babies came back the next day

They were:

• Shown both objects again

• Asked for one object (the one they learned)

👉 Example: “Can you give me the ___?”

Researchers checked:
👉 Did the baby choose the correct object?

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👶 Results: 13-Month-Olds

• They did best when they had:
  👉 IDS + motion together

👉 They needed BOTH cues to remember the word

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💡 Why?

Younger babies:

• Need motion to grab their attention to the object

• Use both what they hear + what they see moving

👉 Motion helps them know:
“This is what the word is referring to”

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👶 Results: 15-Month-Olds

• They did well with:
  👉 IDS alone

👉 Motion was no longer necessary

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💡 Why?

Older babies:

• Already understand:
  👉 “When I hear this kind of speech, I should look at the object”

👉 They don’t need extra help from motion anymore

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🔥 Big Developmental Change

• 13 months → need multiple cues (speech + motion)

• 15 months → can rely on speech alone

👉 Shows improvement in:

• Attention

• Learning efficiency

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🎯 Main Conclusion

IDS helps babies learn words, BUT:

• Younger infants need extra support (motion)

• Older infants can learn from IDS alone

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🔁 Overall Comments on IDS

IDS:

• Organizes attention
  👉 Helps babies focus on the right thing

• Controls arousal
  👉 Can calm or excite babies

• Supports emotional learning
  👉 Babies learn what tones mean

• Supports language learning
  👉 Clear, simple speech helps them learn sounds and structure

• Helps form word–object connections
  👉 Links words to things in the world

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🌍 Big Picture

IDS is part of babies’ everyday environment

👉 They hear it from:

• Parents

• Siblings

• Other adults

👉 Learning happens through:

• Social interaction

• Multiple cues working together (voice + motion + context)

Impact of depressed maternal IDS on infant learning (Kaplan)

🧠 Core Idea

Not all IDS is the same.

👉 If a caregiver is depressed, their speech:

• Is less exaggerated

• Sounds flatter

👉 This can affect how well babies learn from speech

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🧪 Kaplan’s Question

Do babies learn differently depending on the type of speech they hear?

Especially:
👉 Does depressed speech make learning harder?

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🧪 Study Setup

Babies saw this pattern 8 times:

• Hear speech → see a face

• Hear speech → see a face

👉 They learn:
Speech = face is coming

(This is habituation + learning a pattern)

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🔄 Test Trial (9th time)

• Hear speech → see a checkerboard instead

👉 If babies learned the pattern, they should think:
“Wait… I expected a face!”

➡ They should look longer (dishabituate)

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🎯 Key Idea

Dishabituation =
👉 Baby learned the connection (speech → face)

No dishabituation =
👉 Baby did NOT learn the connection

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👶 Condition 1: Own Mother’s Speech If mom is NOT depressed:

• Baby learns the pattern

• Looks longer at checkerboard ✅

👉 Shows learning happened

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If mom IS depressed:

• Baby does NOT learn the pattern

• Does NOT look longer ❌

👉 Depressed speech didn’t help learning

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⚠ Problem (Confound)

Maybe babies just respond differently to:
👉 their own mom’s voice

So researchers tested this further

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👩 Condition 2: Unfamiliar Depressed Voice

• Babies hear a different depressed woman

Result:

• Babies do NOT learn

• No dishabituation ❌

👉 This is true for:

• Babies with depressed moms

• Babies with non-depressed moms

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💡 Meaning

It’s NOT about:

• The baby

• Or their relationship with their mom

👉 It’s about the type of speech itself

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👩 Condition 3: Unfamiliar Non-Depressed Voice

• Babies hear a normal (non-depressed) voice

Result:

• Babies DO learn

• They dishabituate ✅

👉 Even babies with depressed moms can learn here

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🎯 Big Conclusion

Babies CAN learn

BUT:
👉 Learning depends on whether the speech provides good cues

• Non-depressed speech → works

• Depressed speech → doesn’t work as well

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⏳ Developmental Change At 4 months:

• Babies with depressed moms can still learn from
  👉 unfamiliar non-depressed speech

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At 12 months:

• Babies with depressed moms stop learning from female speech altogether

👉 They’ve generalized:
“Female speech isn’t helpful”

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BUT:

• They can still learn from dad’s speech (if not depressed)

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💡 What This Means

There is nothing wrong with the babies

👉 The issue is their acoustic environment

Over time, they learn:

• What speech is worth paying attention to

• What speech to ignore