Visuo-manual pursuit tracking of human two-dimensional movements.

Abstract

We investigated visuo-manual pursuit tracking in 10 adult subjects. The main features of the experi ments were as follows: (a) The targets to be pursued were planar (two-dimensional) trajectories. (b) Targets were based on actual human hand movements. A set of five different extemporaneous movements (scribbles) were rear-projected on a digitizing table with their original timescale. (c) Targets were presented both as originally recorded (Condition N) and after a numerical manipulation that made the tangential velocity constant throughout the motion (Condition T). After a set of de scriptors of the performance suitable for the two-dimensional case was introduced, individual perfor mances were analyzed to characterize both the features common to all subjects and the idiosyncratic differences. The main results of the study were as follows: (a) Performances are extremely consistent across repetitions. Differences among subjects are mostly confined to the value of the descriptors. (b) The single most characteristic descriptor is the instantaneous delay between target and pursuit. The position error depends jointly on this delay and the instantaneous target velocity. (c) The operat ing strategy is significantly modified in Condition T. (d) A simple formal scheme based on the notion of a delayed velocity feedback accounts quite accurately for the experimental results. This is in contrast with most classical models of pursuit tracking.

Nonvisual Motor Learning Improves Visual Motion Perception: Evidence From Violating the Two-Thirds Power Law

“…It thus seems to be possible to execute movements in which velocity and geometry do not match according to the 2/3 power law. This finding is in contrast with previous studies on manual tracking of predictable (Viviani and Mounoud 1990) and unpredictable twodimensional movements (Viviani et al 1987) and in a study in which participants had to reproduce a movement that was imposed on the right arm with the left arm (Viviani et al 1997). These studies demonstrated that it is nearly impossible to produce movements violating the 2/3 power law.…”

“…In contrast to previous studies (Viviani 2002;Viviani and Mounoud 1990;Viviani et al 1987) but similar to findings of Wann et al (1988), the typical curvature-velocity relation as predicted by the 2/3 power law seems to be altered after motor training.…”

Approaches to the Study of Haptic Sensing

“…This observation has been formalized as the "two-thirds power law" relating speed and curvature (Lacquaniti et al 1983;Viviani and Cenzato 1985). It holds even when subjects track moving targets; performance is degraded if the target motion does not conform to this relation (de'Sperati and Viviani 1997;Viviani et al 1987). In fact, this covariation between speed and curvature is maintained qualitatively when subjects trace unknown and unseen curvilinear closed contours (unpublished observations).…”

Biological movements look uniform: Evidence of motor-perceptual interactions.

“…It has been suggested (Hoffman & Flinchbaugh, 1982) that these motor schemes are instrumental for providing a veridical three-dimensional (3D) interpretation of the retinal images. Moreover, further evidence of a motor component in the interpretation of visual information has come from the results of two experiments on visuomanual pursuit tracking (Viviani, Campadelli, & Mounoud, 1987;Viviani & Mounoud, 1990), which show that it is virtually impossible to accurately pursue two-dimensional (2D) targets that do not comply with certain regularities that characterize biological motions.…”