Sensorimotor abilities

Developments in motor skill are some of the most obvious changes we see, in early and later life. Motor abilities are used as a measure of development particularly in infancy. It's notable that motor problems appear in the diagnostic criteria for most developmental disorders.

• Rolls from side to back - average age achieved = 2 months
• Sits alone  = 7 months
• Crawls = 7 months
• Pulls to stand = 8 months
• Stands alone = 11 months
• Walks alone = 12 months
• Walks up stairs with help = 16 months

Early sensorimotor behaviours - neonatal reflexes: e.g sucking, rooting, respiratory occlusion, stepping, moro reflex, and grasping

Rochat & Hespos (1997) found differentialy rooting responses in newborns and 1 month olds. Measured rooting responses following self or other touch, and found different responses to these different types of touch. Rooting may not just be an automatic reflex to specific tactile stimulation

Castiello et al (2010): movements of twins sharing a uterus indicate intentional interactions between them. Increase in movements towards twin between 14 and 18 weeks gestation. Different kinds of movements directed towards twin than towards uterine wall, but similar (slower) kinds of movements to self and twin.

Debate concerns whether motor development proceeds according to predetermined maturational timetables. Maturationists like Arnold Gesel (1880-1961) thought that there was a relatively complete genetic blueprint of motor skills prior to development and that development was mainly a matter of the maturation of that predescribed plan.

Evidence for maturation: fixed trajectories of development. Directions of motor development progress in a cephalocaudal direction - from head the next to lower torso, legs, and feet. Also proximodistal direction - from the shoulders to the hands. Strong reflexes wane and are later replaced by more specific behaviours.

Our motor behaviours are controlled by sensory information. The demands that our environment makes on our motor system vary constantly. Children must navigate obstacles, actively explore the environment, and stand up without falling over.

Over the first year, infants get better at using visual aspects of targets to guide their reaching. Von Hofsten & Fazel-Zandy (1984): 4.5 month olds start showing some orientational adjustment of the hand appropriate to target. Von Hofsten & Ronnqvist (1988): 9 month olds start showing some preparation of grasp aperture to match the size of a target prior to contact. Smyth et al (2004): its not until 7 or 8 years that children use visual information to control their reaches in an adult-like way.

We use both proprioceptive (joint and muscle), vestibular, and visual (optic flow) information to maintain our balance. Optic flow tells us how we are moving relative to our environment, and can be important in balancing.

The visual cliff experiment was designed by Gibson and Walk to investigate depth perception in human and animal species. The visual cliff consists of a sheet of plexiglas that covers a cloth with a high-contrast checkerboard pattern. On one side the cloth is placed immediately beneath the plexiglas, and on the other, it is dropped about 4 feet below. The plexiglas supports the infants weight so the cliff is visual rather than an actual drop-off.

Infants that could not yet locomote could still discriminate between the two sides of the cliff, as demonstrated through cardiac responses. Heart rate increased when placed on the deep side (Campos, Langer & Krowitz, 1970). In babies that can crawl, after 6 weeks of crawling, they will avoid the drop-off.

The original visual cliff study had 36 infants from 6-14 months of age placed on the shallow side of the visual cliff. The caregiver then stood on the other side, calling out for them to come. It was assumed if the child was reluctant to crawl over the "drop-off" to their caregiver, they were able to perceive depth, believing the transparent space was an actual cliff. 27 of the infants crawled over to their mother without any problems. A few crawled but were extremely hesitant. Some infants refused to crawl because they were confused about the perceived drop (Gibson & Walk, 1960).

• There are early links between vision and movement
• A lot of changes in the ways infants and children use visual cues to guide their movements right up into late childhood
• Sensorimotor experience seems to be important in giving rise to these fine-tunings of sensorimotor control

We need perception to inform and control our actions. Our actions influence the ways in which we perceive and think.