Earth-Gravity Congruent Motion Benefits Visual Gain For Parabolic Trajectories

Abstract

There is evidence that humans rely on an earth gravity (9.81 m/s²) prior for a series of tasks involving perception and action, the reason being that gravity helps predict future positions of moving objects. Eye-movements in turn are partially guided by predictions about observed motion. Thus, the question arises whether knowledge about gravity is also used to guide eye-movements: If humans rely on a representation of earth gravity for the control of eye movements, earth-gravity-congruent motion should lead to improved visual pursuit. In a pre-registered experiment, we presented participants (n=10) with parabolic motion governed by six different gravities (-1/0.7/0.85/1/1.15/1.3g), two initial vertical velocities and two initial horizontal velocities in a 3D environment. Participants were instructed to follow the target with their eyes. We tracked their gaze and computed the visual gain (velocity of the eyes divided by velocity of the target) as proxy for the quality of pursuit. An LMM analysis with gravity condition as fixed effect and intercepts varying per subject showed that the gain was lower for -1g than for 1g (by -0.13, SE = 0.005). This model was significantly better than a null model without gravity as fixed effect (p<0.001), supporting our hypothesis. A comparison of 1g and the remaining gravity conditions revealed that 1.15g (by 0.043, SE=0.005) and 1.3g (by 0.065, SE=0.005) were associated with lower gains, while 0.7g (by 0.054, SE=0.005) and 0.85g (by 0.029, SE=0.005) were associated with higher gains. This model was again significantly better than a null model (p<0.001), contradicting our hypothesis. Post-hoc analyses reveal that confounds in the 0.7/0.85/1/1.15/1.3g condition may be responsible for these contradicting results. Despite these discrepancies, our data thus provide some support for the hypothesis that internalized knowledge about earth gravity guides eye movements.

Prediction in goal-directed action

“…The technology for mobile eye tracking and motion capture has become much more accessible, but the number of studies that make use of such technology to systematically and carefully investigate predictive strategies during tasks such as walking (Matthis et al, 2018), driving (Tuhkanen et al, 2019), or ball sports (Diaz, Binaee, & Phillips, 2016;Higuchi et al, 2018) is still quite limited. Combining such technology with virtual or augmented reality can provide experimenters with precise control of sensory variables of interest and allow them to manipulate target features such as ball elasticity or gravity (Diaz et al, 2013;Jörges & López-Moliner, 2019;Russo et al, 2017), while providing an immersive experience mimicking real-world settings. Virtual reality is especially valuable for creating conflict situations in space and time, for example between the proprioceptive and the (virtual) visual feedback of one's own body movements (Ma & Hommel, 2015), to test the flexibility and the limits of sensory prediction of action consequences.…”