Poster #155 - Perceiving Affordances for Walking over Gaps

• In Event: 3-206 - Poster Session 13
  In Poster Session: PS 13 Section - Perceptual, Sensory, Motor

Integrative Statement

When faced with an obstacle, walkers can modify their gait and continue walking, or avoid walking over the obstacle. In previous work, experienced walking infants modified their gait to navigate challenging slopes, drop-offs, and bridges, and avoided walking over impossibly steep slopes, large drop-offs, and narrow bridges (Adolph & Robinson, 2015). For example, experienced walkers take tiny steps to inch across narrow bridges; on impossibly narrow bridges, infants perceive that gait modifications are insufficient and avoid walking. However, previous studies tested infants on obstacles that required them to decrease the amplitude of their walking steps by taking smaller, shorter steps.

Here, we tested infants at the edge of a gap. Infants could modify their gait to walk over the gap—but in contrast to previous work, they would need to increase the amplitude of their steps (Figure 1A)—or avoid walking (Figure 1B). We tested 14- to 19-month-old experienced walkers (M age = 15.8 months, M walking experience = 3.6 months); preliminary N=17, planned N=36. Infants were encouraged to walk repeatedly over 1- to 90-cm wide gaps (M trials = 58.5). Using a psychophysical procedure (see Kretch & Adolph, 2013), we determined the largest gap each infant could successfully walk over—their “gap threshold.” Then, we presented infants with safe gaps (smaller than threshold) and risky gaps (larger than threshold).

As shown in Figure 1C, most infants displayed small gap thresholds (5-12 cm) and a few displayed large ones (16-40 cm). All infants modified their gait as they approached gaps by decreasing step length and velocity. The difference between the small- and large-threshold infants was what they did after stopping at the brink. Infants with small thresholds avoided walking over gaps that required an increase in the amplitude of their steps, whereas infants with large thresholds took a giant step to cross challenging gaps.

Consistent with previous research, infants accurately perceived whether walking was possible. As shown in Figure 1D, attempts to walk decreased with increasing gap size. Infants always attempted to walk over 1-cm gaps, attempted to walk over their threshold gap on M = 56.9% of trials, and rarely attempted gaps larger than threshold (M = 6.5% of trials). Overall, infants attempted to walk on 96.6% of trials on safe gaps, but only 6.5% of trials on risky gaps.

Although our preliminary data indicate that experienced walking infants accurately perceived the limits of their abilities to walk over gaps, most were loathe to modify their walking gait. Instead of increasing step size to cross gaps larger than their typical step length, they avoided walking. These findings contrast with previous research, which showed that experienced walkers perceive the limits of their abilities and execute gait modifications to increase their ability to navigate obstacles. Infants’ inability to take longer steps when needed may be a failure of planning or a result of immature balance. Regardless, increasing movement amplitude—taking larger steps to cope with an obstacle—appears to require more experience and skill than decreasing amplitude.

Authors

• Whitney Graham Cole, New York University
  Presenting Author

• Karen E Adolph, New York University
  Non-Presenting Author