How do reaching and walking costs affect movement path selection?

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.

How are cognitive and physical difficulty compared?

Tasks that require less physical effort are generally preferred over more physically demanding alternatives. Similarly, tasks that require less mental effort are generally preferred over more mentally demanding alternatives. But what happens when one must choose between tasks that entail different kinds of effort, one mainly physical (e.g., carrying buckets) and the other mainly mental (e.g., counting)? We asked participants to choose between a bucket-carrying task and a counting task. Our participants were less likely to choose the bucket task when it required a long reach rather than a short reach, and our participants were also less likely to choose the bucket task the smaller the final count value. We tested the hypothesis that subjective task durations provided a common currency for comparing the difficulties of the two kinds of tasks. We found that this hypothesis provided a better account of the task choice data than did an account that relied on objective task durations. Our study opens the door to a new problem in the study of attention, perception, and psychophysics-judging the difficulty of different kinds of tasks. The approach we took to this problem, which relies on two-alternative forced choice along with modeling the basis for the choice, may prove useful in future investigations.

A method for measuring manual position control.

There is no generally accepted method for measuring manual position control. We developed a method for doing so. We asked university students to hold a handle that had one rotational degree of freedom. The angular position of the handle depended on the degree of pronation-supination of the forearm. The subjects' task was to hold the handle as steadily as possible to keep a needle positioned in a pie-shaped target zone on a computer screen. If the needle remained in the zone for 0.5s, the gain of the feedback loop increased; otherwise the gain decreased or remained at the starting value of 1. Through this adaptive procedure, we estimated the maximum gain that could be achieved at each of the four pronation-supination angles we tested (thumb up, thumb down, thumb in, and thumb out) for each hand. Consistent with previous research on manual control, and so validating our measure, we found that our participants, all of whom were right-handed, were better able to maintain the needle in the target zone when they used the right hand than when they used the left hand and when they used midrange wrist postures (thumb up or in) rather than extreme wrist postures (thumb down or out). The method provides a valid test of manual position control and holds promise for addressing basic-research and practical questions.

Cognitive framing in action.

Cognitive framing effects have been widely reported in higher-level decision-making and have been ascribed to rules of thumb for quick thinking. No such demonstrations have been reported for physical action, as far as we know, but they would be expected if cognition for physical action is fundamentally similar to cognition for higher-level decision-making. To test for such effects, we asked participants to reach for a horizontally-oriented pipe to move it from one height to another while turning the pipe 180° to bring one end (the "business end") to a target on the left or right. From a physical perspective, participants could have always rotated the pipe in the same angular direction no matter which end was the business end; a given participant could have always turned the pipe clockwise or counter-clockwise. Instead, our participants turned the business end counter-clockwise for left targets and clockwise for right targets. Thus, the way the identical physical task was framed altered the way it was performed. This finding is consistent with the hypothesis that cognition for physical action is fundamentally similar to cognition for higher-level decision-making. A tantalizing possibility is that higher-level decision heuristics have roots in the control of physical action, a hypothesis that accords with embodied views of cognition.

Pre-crastination: hastening subgoal completion at the expense of extra physical effort.

In this article, we describe a phenomenon we discovered while conducting experiments on walking and reaching. We asked university students to pick up either of two buckets, one to the left of an alley and one to the right, and to carry the selected bucket to the alley's end. In most trials, one of the buckets was closer to the end point. We emphasized choosing the easier task, expecting participants to prefer the bucket that would be carried a shorter distance. Contrary to our expectation, participants chose the bucket that was closer to the start position, carrying it farther than the other bucket. On the basis of results from nine experiments and participants' reports, we concluded that this seemingly irrational choice reflected a tendency to pre-crastinate, a term we introduce to refer to the hastening of subgoal completion, even at the expense of extra physical effort. Other tasks also reveal this preference, which we ascribe to the desire to reduce working memory loads.