Perceptual judgments of duration of parabolic motions

Abstract

In a 2-alternative forced-choice protocol, observers judged the duration of ball motions shown on an immersive virtual-reality display as approaching in the sagittal plane along parabolic trajectories compatible with Earth gravity effects. In different trials, the ball shifted along the parabolas with one of three different laws of motion: constant tangential velocity, constant vertical velocity, or gravitational acceleration. Only the latter motion was fully consistent with Newton’s laws in the Earth gravitational field, whereas the motions with constant velocity profiles obeyed the spatio-temporal constraint of parabolic paths dictated by gravity but violated the kinematic constraints. We found that the discrimination of duration was accurate and precise for all types of motions, but the discrimination for the trajectories at constant tangential velocity was slightly but significantly more precise than that for the trajectories at gravitational acceleration or constant vertical velocity. The results are compatible with a heuristic internal representation of gravity effects that can be engaged when viewing projectiles shifting along parabolic paths compatible with Earth gravity, irrespective of the specific kinematics. Opportunistic use of a moving frame attached to the target may favour visual tracking of targets with constant tangential velocity, accounting for the slightly superior duration discrimination.

Watching the Effects of Gravity. Vestibular Cortex and the Neural Representation of “Visual” Gravity

“…Indeed, as mentioned above, people systematically underestimate the motion duration of constant speed targets descending along the vertical and activate their arm muscles too early to intercept them (McIntyre et al, 2001 ; Zago et al, 2004 ). The precision of perceptual judgments of the duration of parabolic motions is independent of whether the target moves according to natural gravity or it shifts at a constant speed (Jörges et al, 2021 ). A general heuristic that assumes that descending targets or moving as projectiles are affected by gravity might provide information that is generally good enough while requiring much less cognitive processing or visual resources than exact models of physics (Zago et al, 2008 ; Vicovaro et al, 2021 ).…”

Humans Can Track But Fail to Predict Accelerating Objects

“…For instance, observers are more accurate when tracking and predicting simulated fly balls that move with natural gravity compared with balls that do not (0 g), or that are unnaturally impacted by gravity (2 g; Bosco et al, 2012 ; Russo et al, 2017 ). Although naturalistic priors influence ocular and perceptual motion prediction ( Delle Monache et al, 2019 ), other studies have also found that observers assume that targets move with constant velocity when predicting object motion ( Jörges et al, 2021 ).…”