Affordances are behavior opportunities that delineate a phase transition beyond which a change in behavior requiring muscular reorganization. In the stepping across task, this muscular reorganization enables subjects to put the tip of the shoe as close as possible to the obstacle. But subjects modify step lengths when approaching an obstacle to secure these adequate foot placements. What is the relationship between the perception of the phase transition and the modification of step lengths?

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... experiment consisted of two different tasks. The first involved subjects physically stepping across an obstacle, the second involved subjects judging the step-acrossability of an obstacle when moving towards the given obstacle. The results showed that subjects seemed to perceive the step-acrossability of the obstacle before the initiation of regulation.