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PSYCH 211 (210)
Lecture 4

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University of Waterloo
Mattieu Lecorre

Movement! - Humans are extraordinarily adaptable Learning to move: the typical sequence - Dramatic changes in posture - Baby just sits there o It then can start crawling around o 5% of babies just go from sitting to walking o This is not an absolute sequence that each stage must be visited - How do infants learn to walk? Walking - Pinker says o The way one walks is demanding and a recipe for disaster o As we are walking, we are constantly throwing ourselves forwards and catches ourselves back onto our two feet - Walking requires sophisticated internal “control” program o Why? o How does the program develop? What goes on during Walking - Highly coordinated series of alls - Coordination of 200 skeletal muscles - Back muscles prevent forward fall - Abdominal muscles prevent backward fall - 30 muscles to move one leg and move forward Center of gravity goes up and down, and left and right - Each leg alternates between taking full weight of body and moving freely - Each hip sways backwards and forwards o As change support leg, sway left and right Our gait adapts rapidly to new situations - We are able to use perceptual information to adapt our gait on-line - As we walk, we must adapt to the changes in the environment What happens during walking: Summary - Multiple parts moving in sync o Multiple limbs (eg. Arms & legs) o Joints & muscles within same limb (eg. 30 muscles in leg) - Maintain balance while body changes constantly o Supporting leg alternates between left and right o Centre of gravity goes up and down and left and right o Hips sway backwards and forwards - Make on-line adjustments based on perceptual information o Ice, sand, narrow surface, etc… Why there must be a program that controls walking - The program or “conductor” o Coordinates all the parts in motion o Keeps them balanced o Continuously adjusts their motion and balance according to information about surfaces (ice, sand, concrete, etc.) and changes in body shape (eg. Carrying boxes) coming from senses - How does it develop? o How do we acquire the ability to adapt to new situations? To be able to walk, must wait until shape of body changes - Newborns and young infants are “top heavy” o Relative to size of their body, have very big heads - If tried to walk, would always fall down because of that o Think of how easy it would be to tip over tree with no roots. Baby is the same. - There is a change in head size to body size ratio o Difficult to stand up when young How walking develops: Dynamic systems theory - Walking demands orchestration of many skills o Moving limbs to particular positions o Maintaining balance o Integrating perceptual information, etc. - According to dynamic systems, each skill first redefined on its own, then, once each skill is mastered, babies learn to coordinate them - Do infants really need experience to develop each skill? A few test cases. o Coordinating legs during walking o Using information from senses to maintain balance - Skills to develop so that you will not look silly when walking Stepping: Must babies learn to alternating motion of legs required for walking? - Test: put 6 and 7 month olds who have never walked on a treadmill (babies generally start walking when 12 months old) o Will they just let their legs be dragged backwards? o Or will they walk?  They simply walk like an adult  Shouldn’t be something that babies could imitate walking (visual experience) - If place each leg on separate treadmill moving at different speed, 6 and 7 month olds adapt leg motions o One leg moves faster than other! Maintaining balance - Must use information about position of body in space - Two main sources o “Inner eye”: we can feel our body moving in space even with our eyes closed  Involves perceptual mechanism in inner ear  Semicircular canals: tiny tubes filled with fluid. When we move, fluid moves, and triggers
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