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Abstract
An important window into sensorimotor function is how humans interact with and stop moving projectiles, such as catching a ball. Previous studies have primarily investigated stopping of moving projectiles using either real-world experiments, which are constrained by laws of mechanics, or augmented-reality interception paradigms with massless objects, which do not engage postural responses. The purpose of this dissertation was to develop a virtual paradigm that allows for the decoupling of the mechanical interaction between a projectile and the to systematically probe the relationship between object dynamics and limb motor control. In a series of experiments, we used the Mechanical STopping Of Projectiles (MSTOP) task to simulate the physics of mechanical interactions with projectiles, but not the movement of the hands that are required to stop projectiles in the real-world. We aimed to explore how varying the momentum of the projectile, via changes in speed, acceleration, and virtual mass, affected anticipatory and compensatory motor responses. Our results showed that the amplitude of force and arm muscle activation, both in anticipatory (before the collision) and compensatory (during the collision) phases, are similar to results observed in real-life catching studies: response amplitude increased with the increase in object momentum, regardless of whether the momentum increase was due to object speed, acceleration, or mass. In contrast, the timing of these motor responses in the anticipatory phase, were different to the results observed when interacting with objects in the real-world that experience acceleration due to gravity. Our results showed that participants increased their hand force above baseline levels closer to the time of contact between the hand and the object in anticipation of higher momentum collisions. Finally, our experiments showed, in agreement with previous findings, that the ability to match an objects’ velocity with smooth pursuit eye movements decreased with objects moving at higher speeds, for both objects moving at constant speeds and with acceleration. Together, our experiments present a viable framework for using virtual paradigms to mimic the physics of mechanical interactions needed for stopping a projectile, opening new possibilities for understanding how we prepare and update our visuomotor responses in dynamic environments.