Effects of support surface and optic flow on step-like movements in pre-crawling and crawling infants

• Step-like movements in crawling and pre-crawling infants were affected differently by a surface of support.
• Pre-crawling infants made more step-like movements in the air than on a surface.
• Crawling infants made the same number of step-like movements in the air and on a surface.
• Step-like movements were not influenced by optic flow in crawling or pre-crawling infants.
• The findings are discussed relative to the idea that stepping disappears because the legs become too heavy to lift.

Step-like movements were examined in pre-crawling (n = 9) and crawling (n = 9) 6–13 month-old infants in the air and on a surface in response to a static pattern or optic flows that moved toward or away from the infant. Infants completed six 60-s trials. A significant interaction between locomotor status and support condition revealed that pre-crawling infants made more step-like movements in the air than on a rigid surface. In contrast, crawling infants made an equivalent number of step-like movements in the air and on the surface. Optic flow did not influence the number of step-like movements made by infants. The pre-crawling infant finding is consistent with a finding in a previous study in which two month-old infants were shown to step more in the air than on the ground. This finding is discussed relative to the idea that the infant stepping pattern disappears because the legs become too heavy to lift.