Motor Development

Equifinality and Multifinality

Motor development is traditionally portrayed as a series of stages, but this simple characterization fails to capture the equifinality (multiple pathways to the same endpoint) and multifinality (multiple outcomes from the same starting point) inherent in the developmental process. Infants often arrive at the same outcome through different developmental routes; the mature manifestation of a skill in young adults often takes different forms; and elderly adults commonly compensate for decrements in skill in different ways. Individual differences and intraindividual variability are typical, and cultural differences can be surprisingly dramatic.

Body–Environment Reciprocity

Motor actions depend on the physical constraints of both body and environment. Thus, the development of motor actions reflects changes in the fit between body characteristics and variations in environmental properties. To walk upstairs, for example, the walker’s leg length, muscle strength, balance control, coordination, and endurance must be sufficient relative to the riser height, tread depth, and number of stairs in the staircase. Changes in either side of this reciprocal body–environment relation alter possibilities for action.

Perception–Action Coupling

Motor development involves changes in psychological functions as well as changes in biomechanics. Because body and environmental constraints are continually varying, perception (and sometimes cognition) is required to guide motor actions adaptively. Optimally, movements are controlled prospectively rather than reactively, and such planning and forethought require perceptual information about possibilities for action (e.g., whether a narrow doorway is passable) and upcoming events (e.g., a car swerving into your lane). Exploratory activity and feedback from movements performed moments earlier generate the requisite perceptual information.

Experience

Generally, basic motor skills such as posture, locomotion, and manual actions emerge in infancy, improve over childhood, become more refined during adolescence and young adulthood, and decline with aging. However, motor development is only age related, not age determined, because experience affects the ages when skills first appear (walking onset at 9 or 18 months), the form of each skill (sitting with legs out or in a deep squat), and which skills are acquired (some infants never crawl, and many people never learn to swim, ride a bicycle, or drive a car). Active, self-generated experience is far [Page 1450]more powerful (e.g., children kicking their legs) than experiences that are passively received (caregiver pumping children’s legs). Child-rearing practices and cultural expectations and customs play a large role in determining the amount and variety of experience with particular skills.

Developmental Cascades

Developmental changes in one motor skill can bring about changes in other motor skills and lead to changes in domains seemingly far afield. For example, the ability to sit facilitates multimodal object exploration (e.g., coordinated looking and touching). The advent of crawling instigates improvements in spatial cognition and memory. And the ability to walk stimulates changes in emotional independence and social interactions with caregivers.

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