Motor Development

Question 1

motor development

Answer 1

• Previously believed to be an element of neurological maturity.
  
  • Most researchers now take a dynamic systems theory (DST) approach:
  • Dynamic - change over time
  • System - many elements interacting
  • DST explains how behaviour changes over time.
  • Dynamic systems theory emphasises multiple cases:
  • Increases in strength and weight
  • Neural mechanisms
  • Posture control
  • Balance
  • Perceptual skills
  • Motivation

Question 2

major milestones of infant motor development

Answer 2

• Birth to 5 months:
  
  • Stepping reflex
  • Mini push-ups during tummy time
  • Bounce when held upright
  • 6 to 10 months:
  • Sit up
  • Crawl
  • Stand with support
  • Cruise
  • 9 to 15 months:
  • Pull to a stand
  • Stand unsupported
  • Take first steps
  • 16 to 18 months:
  • Dance
  • Climb stairs with help
  • Walk backward
  • 2 years:
  • Run
  • Kick a ball
  • Jump from low step

Question 3

dynamic systems theory

Answer 3

· Dynamic - change over time
· System - many elements that interact in a complex lawful way
· Goal of dynamic systems theory - explain how behaviour changes lawfully through time.
· Not “when” but “how” development occurs
· Most children arrive at certain milestones - “attractors” (e.g., crawling, standing, and walking), although by way of different routes.
· Paths to attractors can be variable
· The process depends more upon experimentation, curiosity, and learning than was previously thought.

Question 4

motor development is an ongoing process

Answer 4

· Motor skills do not suddenly “turn on”
· How often you measure also leads to different data
In this examples, black = daily measurements, pink/grey = monthly

Question 5

motor skills

Answer 5

· Fine - smaller muscles:
- Grasping (hand)
- Object manipulation
- Drawing
· Gross - large muscles:
- Sitting
- Reaching (arm)
- Crawling
- Walking
- Running

Question 6

stepping reflex

Answer 6

· Infants lift first one leg and then the other
· Coordinated pattern resembling walking
· Alternative leg movements
· Disappears at around 2 months of age
· Infants’ rapid weight gain in the first few weeks causes their legs to get heavier faster than they get stronger.
· DST demonstration - make babies behave like other babies - older babies in water, younger babies with ankle weights
· Know its not neurological maturity because they can do the same behaviour when laying down (distributed gravitational pull).

Question 7

sitting independently

Answer 7

· Sitting independently (no support from arms) aids reaching (Spencer et al, 2000)
· Sitting independently has a cascading effect on infant perception (Ross-Sheehy et al, 2016)
· Sitting creates new opportunities for exploring
· New opportunities for exploring shape visual perception

Question 8

figure/ground assignment

Answer 8

· Figure/ground assignment allows us to identify objects (figures) from the background.
· It helps us understand depth and plan reaching.
· Adults use symmetry, convexity (curvature), lower region to determine figure/ground.
· Infants need figure/ground segregation to guide attention, eye movements and learning.

Question 9

illustrating the dynamic systems view

Answer 9

· Thelen performed two classic experiment to test the hypothesis that rapid weight gain causes disappearing reflex.
1. Weights were attached to ankles of infants who still had the stepping reflex -> babies suddenly stopped stepping
2. Infants who no longer showed the stepping reflex were suspended waist-deep in a tank of water that supported their weight -> reflex appeared
* Hence, the movement pattern and its neural basis remains but is masked by the changing ratio of leg weight to strength.

Question 10

reaching

Answer 10

• Stretching out one or both hands toward something to touch or grasp it (Rohr et al, 2021)
  
  • Initial reaches are swiping movements
  • First, infants are limited to clumsy swiping movements towards the general vicinity of objects.
  • After infants gain the ability to sit independently, then reaching becomes quite stable.
  • With experience, infants’ reaches show signs of anticipation.
  • Their approach is influenced by what they intend to do with the object and its size and material.

Question 11

“soft assumbly” of reaching

Answer 11

• Motor development is not a fixed sequence:
  
  • Variability is okay
  • Variability in when components (e.g., stable base, arm control) come “online”
  • Need all components to “assemble” a successful reach
    Infants’ behaviour not in genes or brain, but in the interaction of the baby-environment system.

Question 12

sticky mittens

Answer 12

· Sticky mittens - have velcro that help children who are not yet reaching make contact with objects.
· Parents were asked to give infants sticky mitten time for 10 min/day for 2 weeks.
· After only one week infants’ in the training group grasps and reached significantly more often that their peers (Libertus and Needham, 2010).

Question 13

A not B

Answer 13

· Piaget created the “A-not-B” task to test 8-10 months infants’ representations
· “A-not-B” task:
- Hide toy at A, infant finds (repeat ~6x)
- Hide toy at B, infant searches A, not B
· Piaget reasoned infants do not have objected permanence until ~10 months

Question 14

DST account of A-not-B

Answer 14

· Behaviour is the product of past history, just previous past and present (“nested timescales”)
· A-not-B error is the result of previous attention to A and practice reaching to A
· DST explanation includes attractors, motor memory, and preservation
· Errors persist if:
- There is no reaching on A
- There are no objects (just wave lids)
- Unmarked locations (sandbox) in 2-4 years
- There are long delays - even in adults
· If you change posture between trials errors are reduced (less reliant on motor memory)

Question 15

(self-) locomotion

Answer 15

· At around 8 months, infants become capable of self-locomotion - they begin to crawl
· Toddlers begin walking independently around 13-14 months, using a toddling gait.

Question 16

motor skills are context dependent

Answer 16

· Adolph (1997) tracked infants in a weekly longitudinal study from early crawling to proficient walking
· Knowledge does not transfer from crawling to walking
· 67% of children plunged down ALL slopes, but did become more cautious with experience
· Knowledge is context dependent

Question 17

the importance of falling

Answer 17

· Falling (errors in balance and motor control) may help us understand the role of errors in early development.
· 138 toddlers (13-19mo) were observed in a laboratory playroom
· Toddlers fell 563 times
· Han & Adolph (2020, Wiley)
· Falling did not alter subsequent behaviour
· After a fall, infants returned to play in 1.84s on average
· Impact was mitigated by small body size, and infants’ quick reactive behaviours (e.g., bracing with hands)
· Infants rarely fussed (4% of falls)
· Caregivers were rarely concerned (8%)
· Walking experience did not predict fussing, caregiver concern or recovery
· Frequent, low-impact errors encourage further practice

Question 18

road crossing

Answer 18

· Children 5-14yrs have higher rates of pedestrian injuries than any other age group (O’Neal et al., 2018)
· Most child pedestrian injuries happen at mid-blocks (e.g., Oxley et a., 2012)
· Shorted path to school often requires crossing mid-block (Bennet & Yiannakoulias, 2015)
· 6-10yr children are much slower than older children and adults to enter a road and also enter roads with much smaller gaps in traffic (O’Neal et al., 2018)

Question 19

crossing road with friends

Answer 19

· Pairs of friends crossed a virtual road 30 times (half on left/right)
· A stream of traffic came from the left at ~40kmh (25mph)
· Traffic included random 2s-5s gaps
· No instructions to cross together or alone
· They could wait to cross as long as they wanted to
· Adolescents took riskier gaps with a friend than alone
· To compensate for short gaps, they entered and crossed faster
When solo, first crossers were more risky (and 12yo first crossers riskier than adults)

Question 20

depth perception/peripheral vision

Answer 20

· Does depth perception emerge before or after crawling?
· How to assess infants depth perception?
· The visual cliff…
· Depth perception emerges after crawling.
· Peripheral vision improves after crawling.

Question 21

scale errors

Answer 21

· Toddlers’ sense of scale is so fragile that their desires can “override” their perception, leading to scale errors (making an action on a miniature replica).

Question 22

slopes

Answer 22

· Karen Adolph and colleagues have found that infants do not transfer what they learned about crawling to walking.
· To examine motor development, Adolph conducted a longitudinal study:
- Followed infants from 1st week of crawling to several good weeks of walking
- Infants came in every week and went over the slopes of different degrees.
· Results - experienced crawlers became more cautious as slopes were more steep
· Knowledge about sloped did not generalise to walking:
- 10 of 15 new walkers plunged down all of the slopes, even though they had been cautious of these slopes as crawlers
- Knowledge of slopes is context (action) specific
- New perceptual behaviours emerge when actions become stable.
· If slope task depends on depth perception, then why are crawlers so bad compared to the visual cliff?:
- Maybe they can detect steepness, but don’t know what it means for actions.
- Crawlers cannot match their perceptual abilities to their action abilities.

Question 23

motor skills summary

Answer 23

· Motor development depends on experimentation, curiosity, and learning by experience
· Many factors need to come together (”soft assembly”)
· Motor development is an ongoing process
· Behaviour is the product of nested timescales

Question 24

motor experience is related to language

Answer 24

· Emergence of sitting correlates with vocabulary at 10mos and 14mos (Libertus & Violi, 2016)
· Emergence of walking correlates with both receptive and productive vocabulary (Walle & Campos, 2014)
· Children who walk make more bids for communication than same-age children who crawl (Clearfield, Osborne & Mullen, 2008)
6-12-year-olds remember new vocabulary better if they exercise after learning the new words (Pruitt & Morini, 2021)