Why does infant stepping disappear and can it be stimulated by optic flow?

Area of Science:

• Developmental psychology
• Infant motor development
• Visual perception

Background:

• The disappearance of infant stepping reflexes around two months is often attributed to the 'heavy legs' hypothesis.
• Limited research exists on the specific kinematic differences and visual influences on early infant stepping.

Purpose of the Study:

• To investigate infant stepping movements when supported in air versus on a surface.
• To examine the effect of optic flow (visual input) on infant stepping and related movements.
• To challenge the prevailing explanation for the cessation of the stepping reflex.

Main Methods:

• Two experiments were conducted with 2-month-old infants (n=22 each).
• Infants were supported upright in air and on a surface to compare stepping movements.
• Kinematic analysis was performed on air- and surface-stepping.
• Infants were exposed to optic flows specifying forward or backward translation to observe effects on stepping and donkey kicks.

Main Results:

• Infants exhibited significantly more stepping movements when suspended in air compared to when their feet contacted a surface.
• Kinematics of air- and surface-stepping were found to be similar.
• More air steps and donkey kicks occurred when infants perceived backward visual translation compared to forward translation.

Conclusions:

• The 'heavy legs' explanation for the disappearance of infant stepping is challenged by these findings.
• Infant stepping movements are influenced by visual information, suggesting a role for visual control.
• New questions arise regarding the mechanisms underlying visual control of early motor behaviors in infants.