How do reaching and walking costs affect movement path selection?

Abstract

Although reaching and walking are commonly coordinated, their coordination has been little studied. We investigated decision-making related to reaching and walking in connection with a recently discovered phenomenon called pre-crastination—the tendency to expend extra effort in the service of hastening goal or sub-goal completion. In the earlier studies where pre-crastination was discovered, participants decided which of two buckets to carry to the end of a walkway, picking the bucket they thought was easier. Surprisingly, the majority of participants chose to carry the bucket that was closer to the start position, which meant that the bucket they chose had to be carried farther than the bucket they did not choose. Here we inquired into participants’ sensitivity to reaching effort and walking effort by varying how far participants had to reach to pick up a bucket, how heavy the bucket was, and how far participants had to walk with the bucket they chose. We found that participants were willing to lean and reach far to pick up an empty bucket that was a shorter walk from the start position. However, as reaching costs and carrying costs increased, participants prioritized shorter reaches over shorter walking distances. The results show that although pre-crastination is a robust tendency, there are limits to the kinds of costs people are willing to incur to complete sub-goals as soon as possible.