What factors influence movement or action? Biomechanical (e.g., size, shape, mass, strength, flexibility,…

What factors influence movement or action?

• Biomechanical (e.g., size, shape, mass, strength, flexibility, coordination of body/body parts)

• Environmental (e.g., effects of gravity; surfaces that provide support for the body; objects toward which movements are directed)

• Both of these factors are continually changing

– Rapid and episodic changes in physical growth over the first two years

– Possibilities for interactions with the environment change with changes in infants’ growth and skills

Role of Perception in Action:

• Perception provides current information about both biomechanical and environmental constraints on action

– Allows actions to be planned (prospective)

• Feedback from prior movements used to anticipate the consequences of future actions

• Motor Development as a Perception-Action System

– How do infants detect and adapt to changes in their physical characteristics (biomechanical factors) and to changes in the environment?

• Vary perceptual information by manipulating infants’ physical characteristics (e.g., weighting infants down with backpacks) or by altering properties of the environment (e.g., changing surfaces)

Perceptual Control of Crawling

• Any action requires perceptual control of balance

– To maintain balance, need support to prevent falling

• Visual Cliff (Gibson & Walk, 1960)

– Provides visual depth cues that balance is not possible (past a certain point)

– Crawling experience is related to avoidance of the visual cliff

• Adolph (2000)

– Tested infants on a “real” cliff

• Visual and haptic information are consistent: Looks risky, feels risky

• Adjustable “gap”

• Can test infants in multiple trials

• Tested 9-month-old infants

– Average time sitting: 3 months– Average time crawling: 1 month

• Balance control depends on experience with specific postures

– Infants maintained balance while sitting but “fell” over the cliff while crawling

Walking

• Perceptual Control of Upright Balance

– Visual motion information from optic flow is important for balance control in standing and walking

• Locomotor experience is related to infants’ sensitivity to different types of optic flow

• Peripheral flow information is important for keeping balance– Infants with crawling experience react more strongly (show

more postural sway) to peripheral flow

• Prospective Control of Balance

– Optic flow information allows infants to control balance reactively

– Ideally, balance control should be prospective (i.e., adjustments occur before beginning to fall)

• Experience is related to prospective control of balance

– But experience in one posture (e.g., crawling) does not transfer to other postures (e.g., walking)

• What is critical for motor development?

– Infants must learn to discriminate actions that are possible from those that are not

– In some cases, infant learning seems to be posture-specific and does not transfer to novel contexts

• i.e., what infants learn about maintaining balance while sitting does not help them when they start crawling, crawling knowledge does not transfer to walking, etc.

– But in other cases, learning does transfer

• What are the processes underlying infants’ learning?

• Affordances: Possibilities for action

– Ex: a flat surface affords walking; a 90-degree slope does not afford walking (but may afford climbing)

• Affordances reflect the objective state of affairs regarding infants’ physical capabilities (biomechanical factors) and relevant features of the environment (environmental factors)

• A critical task in motor development is learning to perceive affordances prospectively

– Makes it possible for infants to select appropriate actions to meet goals

– But it is a difficult task, particularly because of the rapid changes in biomechanical and environmental factors for infants

• Infants’ bodies and skills and the environments to which they are exposed are constantly changing

• Experience with specific postures is critical for perceiving affordances prospectively (i.e., knowing what actions are possible or impossible)

• But what are infants learning from experience?

Possible Answers

• Learning that the experimenter will catch them? (i.e., in the “slopes” and “gaps” studies)– But infants in longitudinal studies became

more cautious over sessions– Similarly, infants in cross-sectional studies

who were “rescued” multiple times in their inexperienced posture avoided risky actions in their experienced posture

• Learning fear of heights?

– But infants often don’t show behavioral indices of fear when they avoid risky actions

• Facial expressions are primarily positive or neutral whether infants avoid the risky action or not

• Learning that sudden drop-offs, steep slopes, etc., are dangerous?

– But posture-specific learning suggests that infants are not simply learning facts about the environment that guide their actions

• e.g., infants always require a sturdy floor to support their bodies; a 50 degree slope or a 90-cm gap is risky for every infant in every posture

– But infants don’t seem to generalize these “facts” from one posture to another

– Also, infants often display flexibility within postures

• Ex: backpack study (Adolph & Avolio, 2000)

– Experienced walkers were able to adjust their perception of affordances from trial to trial

» Treated the same slope as risky while wearing lead-weighted shoulder packs and as safe while wearing feather-weighted packs

– Suggests that infants are not learning “static” facts about their physical capabilities

– In addition, infants show a variety of responses in studies in which infants are confronted with obstacles to locomotion

• Ex: Experienced walkers display a variety of strategies for negotiating risky slopes—e.g., crawling down on hands and knees, sliding in the “Superman” position, backing down, sliding in a sitting position, grabbing the experimenter, or avoiding the slope (Adolph, 1995, 1997)

– Individual infants use multiple strategies on the same slope on different trials within the same test session

– Suggests that infants are not learning simple stimulus-response associations or fixed patterns of responding

• Adolph & Eppler (2002):

– Novelty and variability of motor actions cannot be accounted for by simple association learning

– Harlow’s (1949, 1959) idea of “learning sets” is a better model for motor development

• Learners acquire a set of exploratory procedures and strategies for figuring out solutions to novel problems within a particular problem space

• Scope of transfer should be limited to similar problems/tasks

• Adolph & Eppler (2002)

– Infants assemble a repertoire of exploratory behaviors to generate the required perceptual information to perceive affordances

• Perceptual information specifies infants’ physical capabilities (biomechanical factors) and environmental factors

• To the extent that each posture functions as a separate perception-action system, perceptual information will fail to transfer (Adolph, 2002, 2005)

• To detect affordances, sensitivity to perceptual information is required

– Sensitivity to some perceptual information is present at birth, but is refined with experience

• Ex: postural sway in response to peripheral optic flow

• Exploratory behaviors help to generate perceptual information

– Exs: Crawling and walking infants (at all age levels and experience levels) show longer latencies to action and more looking and touching as they approach risky slopes compared with safe ones

• Walkers generate visual and mechanical information by standing with their feet straddling the brink and rocking back and forth over their ankles; crawlers lean forward with both hands on the slope and rock over their wrists

• Infants use perceptual information to perceive affordances and guide action