Object motion influences feedforward motor responses during mechanical stopping of virtual projectiles: A preliminary study

Abstract

An important window into sensorimotor function is how we catch moving objects. Studies that examined catching of free-falling objects report that the timing of the motor response is independent of the momentum of the projectile, whereas the motor response amplitude scales with projectile momentum. However, this pattern may not be a general strategy of catching since objects accelerate under gravity in a characteristic manner (unlike object motion in the horizontal plane) and the human visual motion-processing system is not adept at encoding acceleration. Accordingly, we developed a new experimental paradigm using a robotic manipulandum and augmented reality where participants stabilized against the impact of a virtual object moving at constant velocity in the horizontal plane. Participants needed to apply an impulse that mirrored the object momentum to bring it to rest and received explicit feedback on their performance. In different blocks, object momentum was varied by an increase in its speed or mass. In contrast to previous reports on free falling objects, we observed that increasing object speed caused earlier onset of arm muscle activity and limb force relative to the impending time to contact. Also, arm force increased as a function of target momentum linked to changes in speed or mass. Our results demonstrate velocity-dependent timing to catch objects and a complex pattern of scaling to momentum.

Predictive posture stabilization before contact with moving objects: equivalence of smooth pursuit tracking and peripheral vision

“…Hand kinematics and kinetics were recorded at 1,000 Hz. The virtual moving stimuli was generated using a Gabor-patch generator (https://www.cogsci.nl/gaborgenerator), with properties identical to those in our previous studies (3,4).…”

“…We employed a task called the Mechanical Stopping of a Virtual Projectile (MSTOP) (3,4), where participants had to stop a virtual object moving towards them at a steady velocity. This task was designed to simulate the physical interaction with an object by assigning it a virtual mass.…”

“…In our previous work, we addressed how humans estimate object motion to prepare APAs (3,4). Humans process motion through signals received directly from the eyes (retinal signals) when motion signals of object images moving across the retina (see Fig.…”

Smooth pursuit eye movements contribute to anticipatory force control during mechanical stopping of moving objects

“…After the start position was reached, a background load (4 N in the -Y direction) was applied and stayed on for the remainder of the trial. Background loads of 4N were applied to stabilize the hand prior to the presentation of the moving object (35)(36)(37) and to minimize unnecessary anticipatory hand movements that would affect the measurement of force onset. Then a fixation cross appeared along the midline 19 cm from the start position further away from the body.…”