Braking reaching movements : a test of the constant tau-dot strategy under different viewing conditions.
Following F. Zaal and R. J. Bootsma (1995), the authors studied whether the decelerative phase of a reaching movement could he modeled as a constant tau-dot strategy resulting in a soft collision with the object. Specifically. they investigated whether that strategy is sustained over different viewing conditions. Participants (N =11 ) were required to reach for 15- and 50-mm objects at 2 different distances under 3 conditions in which visual availability of the immediate environment and of the reaching hand were varied. Tau-dot estimates and goodness-of-fit were highly similar across the 3 conditions. Only within-participant variability of tau-dot estimates was increased when environmental cues were removed. That finding suggests that the motor system uses a tau-dot strategy involving the intermodal (i.e., visual. pro-prioceptive. or both) specification of information to regulate the decelerative phase of reaching under restricted viewing conditions. The authors provide recommendations for improving the derivation of t<sub>x</sub> estimates and stress the need for further research on how time-to-contact information is used in the regulation of the dynamics of actions such as reaching.
