Reach-to-grasp movements during obstacle avoidance

Abstract

The transport and grip components are two controlled components of a prehensile movement. These components are coordinated so that objects of varying size and shape resting in diverse locations can be grasped easily. It has been suggested that the timing between these two components is a specified parameter, although the origin of such timing is unknown. The present study examines the interdependency of the reach and grasp components when the transport component is modified by placing an obstacle of varying height (9 cm and 11 cm) in the hand path between the starting position and the target object location. Subjects were asked to reach over a Plexiglas barrier and grasp a 2-cm dowel. To reach the object, the subject had to elevate the hand. At issue in this experiment is whether changes in hand path trajectory caused by obstacle avoidance produce corresponding changes in the kinematics of grip aperture. The findings showed that reaching in the presence of an obstacle resulted in the prolongation of most transport component time parameters except peak acceleration and a few amplitude parameters. Changes in the transport component also produced systematic prolongation in all time parameters of grip kinematics, including grip closure time. Temporal prolongation was also reflected in a significant decrease in grip opening and closing velocity; only relative time-to-peak closing velocity was maintained. Closure distance and maximum grip aperture were smaller for the obstacle conditions. Together with the observed smaller variability for the distance to peak aperture, these findings suggest that spatial localization of the hand aperture is an important prehensile movement control feature. Parameterization processes for the grip component are closely linked to those of the transport component, and their organization appears to be interdependent.

Effect of speed manipulation on the control of aperture closure during reach-to-grasp movements

“…It may be possible that the aperture closure distance could be altered, if a much greater range of transport speed were examined. Similar to our previous studies (Alberts et al 2000(Alberts et al , 2002Rand et al 2004;Saling et al 1998;Stelmach 1998, 2001), the current study examines whether transport-grasp coordination is better formulated in terms of spatial or in terms of temporal characteristics of the movement by comparing the extent of invariance in those characteristics with regard to transport speed and distance. For this purpose, in this study we expanded the range of speed manipulations from that previously tested and examined how the aperture closure distance varied across that range.…”

“…More specifically, the grip aperture is modulated based on the distance between the hand and the object. Recent studies from our laboratory support this view by demonstrating an invariant nature of the hand location relative to the object where the aperture begins to close (Alberts et al 2000(Alberts et al , 2002Rand and Stelmach 2005;Saling et al 1998;Stelmach 1998, 2001). It was shown that the distance traveled by the wrist after maximum aperture (aperture closure distance) was relatively invariant, even though the distance traveled by the wrist prior to maximum aperture varied under different task constraints.…”

“…It was shown that the distance traveled by the wrist after maximum aperture (aperture closure distance) was relatively invariant, even though the distance traveled by the wrist prior to maximum aperture varied under different task constraints. This was observed in experiments that employed different target sizes and target distances (Alberts et al 2000;Stelmach 1998, 2001), different involvements of body segments Stelmach 1998, 2001), a forearm rotation during the reach (Rand and Stelmach 2005), different conditions for obstacle avoidance (Alberts et al 2002;Saling et al 1998), and with or without mechanical perturbations applied on the reaching arm . These findings were interpreted as evidence that the onset of aperture closure is controlled by spatial information regarding the hand location relative to the object, and hence the transport and grasp components are coordinated primarily in the spatial domain.…”

Learning robotic eye–arm–hand coordination from human demonstration: a coupled dynamical systems approach

“…Tresilian (1998) interprets these effects as subtle adjustments of the transport and grip components which support obstacle avoidance. In their obstacle avoidance experiment, Saling et al (1998) observed a systematic high correlation of arm transport parameters (transport time, time to peak velocity, time to peak acceleration, etc.) with almost all grip kinematic parameters (grip closure time, time to peak aperture, time to peak opening velocity, grip opening velocity, etc.).…”

“…12). Our approach for adapting the reaching hand motion to avoid obstacles is motivated by several studies that have reported significant effects of the obstacle on all aspects of grasp kinematics (e.g., grip duration, grip aperture, time to peak aperture and distance to peak aperture) (Saling et al 1998;Tresilian 1998;Mon-Williams et al 2001). Tresilian (1998) interprets these effects as subtle adjustments of the transport and grip components which support obstacle avoidance.…”