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)

• 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

• 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?

• Can examine by varying perceptual information through 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

In general, 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 they 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

• 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