Intercepting virtual balls approaching under different gravity conditions: evidence for spatial prediction

Abstract

To accurately time motor responses when intercepting falling balls we rely on an internal model of gravity. However, whether and how such a model is also used to estimate the spatial location of interception is still an open question. Here we addressed this issue by asking 25 participants to intercept balls projected from a fixed location 6 m in front of them and approaching along trajectories with different arrival locations, flight durations, and gravity accelerations (0 and 1). The trajectories were displayed in an immersive virtual reality system with a wide field of view. Participants intercepted approaching balls with a racket, and they were free to choose the time and place of interception. We found that participants often achieved a better performance with 1 than 0 balls. Moreover, the interception points were distributed along the direction of a 1 path for both 1 and 0 balls. In the latter case, interceptions tended to cluster on the upper half of the racket, indicating that participants aimed at a lower position than the actual 0 path. These results suggest that an internal model of gravity was probably used in predicting the interception locations. However, we found that the difference in performance between 1 and 0 balls was modulated by flight duration, the difference being larger for faster balls. In addition, the number of peaks in the hand speed profiles increased with flight duration, suggesting that visual information was used to adjust the motor response, correcting the prediction to some extent. Here we show that an internal model of gravity plays a key role in predicting where to intercept a fast-moving target. Participants also assumed an accelerated motion when intercepting balls approaching in a virtual environment at constant velocity. We also show that the role of visual information in guiding interceptive movement increases when more time is available.

Ocular tracking of occluded ballistic trajectories: Effects of visual context and of target law of motion

“…The ball was batted by the hitter located at the bottom left corner of the scene. Stationary graphic elements-such as the perimeter of the baseball field, the players, and the overall landscape-provided perspective view and metric cues ( Figure 1A; for further details, see Bosco et al, 2012;Delle Monache et al, 2015, 2017.…”

Body orientation contributes to modelling the effects of gravity for target interception in humans

“…; Jörges and López‐Moliner ; Russo et al . ; Zago et al . 2011), optimal control of reaching movements (Gaveau et al .…”

“…An internal model of gravity is required because no single sensor can distinguish between gravitational and inertial accelerations according to Einstein's equivalence principle. Indeed, an internal model of gravity has been shown to contribute to interceptions of falling targets (Lacquaniti et al 1993;Tresilian 1997;McIntyre et al 2001;Zago et al 2004;Indovina et al 2005;Jörges and López-Moliner 2017;Russo et al 2017;Zago et al 2011), optimal control of reaching movements (Gaveau et al 2016), perceived duration of gravitational motion (Moscatelli & Lacquaniti 2011), time-to-passage estimates during visual self-motion , naturalness judgments of motion under gravity (La Scaleia et al 2014b;Ceccarelli et al 2018), interpretation of biological motion (Troje & Chang 2013;Maffei et al 2015) and perception of the visual vertical (Van Pelt et al 2005;De Vrijer et al 2008).…”

Motion direction, luminance contrast, and speed perception: An unexpected meeting

“…Astronauts initiate catching movements earlier in microgravity than on Earth, as if they expected a priori the effects of gravity on target motion even when absent (McIntyre, Zago, Berthoz, & Lacquaniti, 2001). Likewise, motion direction with respect to gravity and target acceleration influence the estimate of the time to contact in catching tasks in virtual reality (Russo et al, 2017;Senot, Zago, Lacquaniti, & McIntyre, 2005;Zago et al, 2004).…”