Abstract
The present study investigated differences in the pickup of information about the size and location of an obstacle in the path of locomotion. The main hypothesis was that information about obstacle location is most useful when it is sampled at a specific time during the approach phase, whereas information about obstacle size can be sampled at any point during the last few steps. Subjects approached and stepped over obstacles in a virtual environment viewed through a head-mounted display. In Experiment 1, a horizontal line on the ground indicating obstacle location was visible throughout the trial while information about obstacle height and depth was available only while the subject was passing through a viewing window located at one of four locations along the subject’s path. Subjects exhibited more cautious behavior when the obstacle did not become visible until they were within one step length, but walking behavior was at most weakly affected in the other viewing window conditions. In Experiment 2, the horizontal line indicating obstacle location was removed, such that no information about the obstacle (size or location) was available outside of the viewing window. Subjects adopted a more cautious strategy compared to Experiment 1 and differences between the viewing window conditions and the full vision control condition were observed across several measures. The differences in walking behavior and performance across the two experiments support the hypothesis that walkers have greater flexibility in when they can sample information about obstacle size compared to location. Such flexibility may impact gaze and locomotor control strategies, especially in more complex environments with multiple objects and obstacles.
Highlights
To successfully navigate through complex environments in the natural world, humans and other animals must adapt their movements to the conditions that are encountered at the present moment and in the near future
There were, small differences in trail foot placement before the obstacle across variations in obstacle depth, suggesting that additional work is needed to better understand how far in advance walkers need information about the dimensions of the obstacle. These findings suggest that walkers may be able to sample information about obstacle size early during the approach or much later with no significant consequences for their ability to successfully cross obstacles of various sizes
The model with depth and viewing window was superior to the model with viewing window (χ2(1) = 6.02, p
Summary
To successfully navigate through complex environments in the natural world, humans and other animals must adapt their movements to the conditions that are encountered at the present moment and in the near future. A safety conscious hiker faced with a choice of which of two routes to follow may prefer the one that is initially more difficult if the alternative option eventually leads to a steep slope that lacks secure footing. The pickup of visual information about size and location during approach to an obstacle be faced with an unfortunate dilemma: to turn back, making an energetically costly corrective adjustment, or to attempt to scale the unsafe slope without injury and at great energetic cost. Sudden and unexpected changes to foot placement are energetically costly, and introduce instability that could lead to falling. Avoiding these sudden adjustments requires the advanced sampling of the visual information necessary for guiding gait in the presence upcoming obstacles in a feedforward manner
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