Why Does Infant Stepping Disappear and Can It Be Stimulated by Optic Flow?

Abstract

Two independent experiments (n = 22 and n = 22) showed that 2-month-old infants displayed significantly more stepping movements when supported upright in the air than when supported with their feet contacting a surface. Air- and surface-stepping kinematics were quite similar (Experiment 2). In addition, when data were collapsed across both experiments, more air steps and more donkey kicks were seen when infants were exposed to optic flows that specified backward compared to forward translation. The findings challenge the currently accepted heavy legs explanation for the disappearance of stepping at 2 months of age and raise new questions about the visual control of stepping.

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

“…Curiously, the amount of air stepping in the approaching optic flow condition was the lowest in the three air stepping conditions, just the opposite of what was observed in newborns (Barbu-Roth et al, 2009, 2013), and seemingly inconsistent with recent reports of enhanced tactile stepping frequency and quality in infants as young as two months of age (with and without disabilities) when optic flow is added to the treadmill on which they are stepping (Pantall, Teulier, Smith, Moerchen, & Ulrich, 2011; Pantall, Teulier, & Ulrich, 2012; Teulier, Barbu-Roth, & Anderson, 2014). Barbu-Roth et al (2015) did not have a tenable explanation for the effects of optic flow they observed in their two month-olds.…”

“…Despite the convincing nature of the evidence provided by Thelen and colleagues to support the heavy legs hypothesis, recent findings reported by Barbu-Roth et al (2015) suggest the hypothesis may need modification. Barbu-Roth et al found that two month-old infants stepped significantly more when held upright in the air than when supported upright on a rigid surface.…”

“…They argued that inability to lift the legs couldn’t be the only explanation for the greater amounts of stepping observed in the air than on the surface because if the legs were too heavy to lift on the surface they must have been too heavy to lift in the air. While acknowledging that heavy legs may have helped to depress stepping on the surface, Barbu-Roth et al (2015) argued that the primary reason stepping was inhibited on the surface was not because the infants could not lift the legs, though heavy legs certainly could have factored into the explanation, but because the infants had a tendency to collapse their legs (flex the hips and knees) when lowered in the upright position onto the surface. In other words, the infants were either unable or unwilling to support their body weight on the surface and stepping was not seen because the infants didn’t adopt a posture from which stepping could be initiated.…”

“…Barbu-Roth et al (2015) also examined whether air stepping in their two month-olds was influenced by approaching and receding optic flows, following earlier studies that showed newborns engaged in more air stepping in response to terrestrial optic flows than to a static pattern (Barbu-Roth, Anderson, Desprès, Provasi, Cabrol, & Campos, 2009; Barbu-Roth et al, 2013). Their findings on two month-olds were difficult to interpret.…”

“…The current exploratory study sought to extend the methodology used by Barbu-Roth et al (2015) to older infants with and without hands-and-knees crawling experience using a balanced design in which two levels of postural support (Air and Surface) were crossed with three levels of optic flow (Static, Approaching, and Receding). We were interested in whether older infants would continue to make more step-like movements in the air than on a surface and whether the infant’s locomotor status would influence their behavior in the two contexts.…”