Sources of variability in interceptive movements

Abstract

In order to successfully intercept a moving target one must be at the right place at the right time. But simply being there is seldom enough. One usually needs to make contact in a certain manner, for instance to hit the target in a certain direction. How this is best achieved depends on the exact task, but to get an idea of what factors may limit performance we asked people to hit a moving virtual disk through a virtual goal, and analysed the spatial and temporal variability in the way in which they did so. We estimated that for our task the standard deviations in timing and spatial accuracy are about 20 ms and 5 mm. Additional variability arises from individual movements being planned slightly differently and being adjusted during execution. We argue that the way that our subjects moved was precisely tailored to the task demands, and that the movement accuracy is not only limited by the muscles and their activation, but also-and probably even mainlyby the resolution of visual perception.

How the required precision influences the way we intercept a moving object

“…The spatial standard deviation of 2.8 mm is similar to the values found in some earlier studies Smeets 2007, 2011b) but poorer performance has also been reported (Brenner and Smeets 2009). The temporal standard deviation of 8 ms (corresponding to 3.2 mm of target motion) is also better than many estimates of human temporal precision Smeets 2009, 2011b), although slightly more precise performance has also been reported McLeod and Jenkins 1991).…”

How timely can our hand movements be?

“…Our results in temporal and spatial precision are not very different from the ones obtained by Brenner and Smeets (2009) for interception tasks. In their experiments subjects saw a disk that moved at 20 cm/s and they had to hit it into a goal while being allowed to see their hand during the whole movement.…”

Catching a gently thrown ball

“…The distinction emerges because performance is only poorer when we block vision for some time between the time that the first prediction can be made and the last moment at which new visual information can lead to useful adjustments. Normally, people will continuously adjust their movements on the basis of continuously updated predictions (Smeets and Brenner 1995;Brenner and Smeets 2009).…”