Eye movements and manual interception of ballistic trajectories: effects of law of motion perturbations and occlusions

Abstract

Manual interceptions are known to depend critically on integration of visual feedback information and experience-based predictions of the interceptive event. Within this framework, coupling between gaze and limb movements might also contribute to the interceptive outcome, since eye movements afford acquisition of high-resolution visual information. We investigated this issue by analyzing subjects' head-fixed oculomotor behavior during manual interceptions. Subjects moved a mouse cursor to intercept computer-generated ballistic trajectories either congruent with Earth's gravity or perturbed with weightlessness (0 g) or hypergravity (2 g) effects. In separate sessions, trajectories were either fully visible or occluded before interception to enforce visual prediction. Subjects' oculomotor behavior was classified in terms of amounts of time they gazed at different visual targets and of overall number of saccades. Then, by way of multivariate analyses, we assessed the following: (1) whether eye movement patterns depended on targets' laws of motion and occlusions; and (2) whether interceptive performance was related to the oculomotor behavior. First, we found that eye movement patterns depended significantly on targets' laws of motion and occlusion, suggesting predictive mechanisms. Second, subjects coupled differently oculomotor and interceptive behavior depending on whether targets were visible or occluded. With visible targets, subjects made smaller interceptive errors if they gazed longer at the mouse cursor. Instead, with occluded targets, they achieved better performance by increasing the target's tracking accuracy and by avoiding gaze shifts near interception, suggesting that precise ocular tracking provided better trajectory predictions for the interceptive response.

Gravity as a Strong Prior: Implications for Perception and Action

“…), another physical variable came into focus: (earth) gravity. Gravitational biases have been reported for free falling targets (McIntyre et al, 2001; Zago et al, 2005, 2008, 2010, 2011) as well as for parabolic trajectories (Bosco et al, 2012; Diaz et al, 2013; Delle Monache et al, 2014; de la Malla and López-Moliner, 2015; Lacquaniti et al, 2015, validated a gravity based model for parabolic interception brought forward in Gómez and López-Moliner, 2013), objects on ramps (Mijatović et al, 2014), and even for objects that move horizontally (De Sá Teixeira et al, 2013; De Sá Teixeira, 2016). Interestingly, there seem to be certain constraints as to when computations can access the internal representation of gravity; when the so called “idiotropic vector” along the vertical body axis, for example, is not aligned with the direction of gravity, the contribution of the internal representation of gravity decreases (De Sá Teixeira, 2014; De Sá Teixeira and Hecht, 2014).…”

“…In the wake of this observation, some recent studies investigated parabolic and other trajectories: trajectories. Bosco et al (2012) introduced a combination of weightlessness and hypergravity perturbances and occlusions in 1g trajectories and reported earth gravity biases for interception; (Delle Monache et al, 2014) used eye tracking in a similar design and showed predictive effects of an internal presentation of gravity. A paradigm based on an initial parabolic trajectory and several bounces in combination with eye tracking revealed that gaze movements were consistent with earth gravity based predictions of the ball’s position (Diaz et al, 2013).…”

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.…”

“…where x and y represent the coordinates of either eye or ball position, as indicated in subscript (Mrotek & Soechting, 2007;Delle Monache et al, 2015). Briefly, we computed f s ð Þ for each bin of the pursuit bout by varying the value of s 6200 ms around the time t of the given bin.…”

Earth-Gravity Congruent Motion Benefits Visual Gain For Parabolic Trajectories

“…If gaze behavior is influenced by prediction and an "internal model of gravity" or "earth gravity prior" (Jörges & López-Moliner, 2017) drives prediction in many different computations, then this internal representation of 1g should allow humans to follow targets more closely when their trajectories are governed by earth gravity. And indeed, this line of reasoning has recently been brought into focus: (Delle Monache, Lacquaniti, & Bosco, 2014) presented participants with targets moving along parabolic trajectories that were generally governed by earth gravity. In the second half, a perturbation with 0g or 2g could occur.…”