Hand forces and placement are modulated and covary during anticipatory control of bimanual manipulation

Abstract

Dexterous object manipulation relies on the feedforward and feedback control of kinetics (forces) and kinematics (hand shaping and digit placement). Lifting objects with an uneven mass distribution involves the generation of compensatory moments at object lift-off to counter object torques. This is accomplished through the modulation and covariation of digit forces and placement, which has been shown to be a general feature of unimanual manipulation. These feedforward anticipatory processes occur before performance-specific feedback. Whether this adaptation is a feature unique to unimanual dexterous manipulation or general across unimanual and bimanual manipulation is not known. We investigated the generation of compensatory moments through hand placement and force modulation during bimanual manipulation of an object with variable center of mass. Participants were instructed to prevent object roll during the lift. Similar to unimanual grasping, we found modulation and covariation of hand forces and placement for successful performance. Thus this motor adaptation of the anticipatory control of compensatory moment is a general feature across unimanual and bimanual effectors. Our results highlight the involvement of high-level representation of manipulation goals and underscore a sensorimotor circuitry for anticipatory control through a continuum of force and placement modulation of object manipulation across a range of effectors. NEW & NOTEWORTHY This is the first study, to our knowledge, to show that successful bimanual manipulation of objects with asymmetrical centers of mass is performed through the modulation and covariation of hand forces and placements to generate compensatory moments. Digit force-to-placement modulation is thus a general phenomenon across multiple effectors, such as the fingers of one hand, and both hands. This adds to our understanding of integrating low-level internal representations of object properties into high-level task representations.

Anticipatory Motor Planning and Control of Grasp in Children with Unilateral Spastic Cerebral Palsy

“…In healthy adults, compensatory torques are achieved with a combination of force scaling and digit positioning along a spectrum (e.g., [ 18 , 31 , 36 ]; i.e., they use motor equivalence [ 22 ]). Given this flexibility, on trials where the digits are more collinear, the LFs are partitioned during lift-off to a greater extent.…”

“…Despite the reduced magnitude of scaling of digit positions in the USCP groups when the COM was on the side of the thumb, they showed similar covariation of digit placement and forces to controls, which did not support our hypothesis. However, the covariation between digit placement and forces was less compared to healthy adults (typically 0.8 to 0.9) [ 18 , 31 , 36 ], likely reflecting continued development of grasp coordination until adolescence [ 8 ]. Alternatively, it could be due to the considerably lower external torque of the object compared to ones used in adult studies (e.g., [ 20 , 21 ]).…”

Handlebar Robotic System for Bimanual Motor Control and Learning Research

“…These inconsistent results between robotic assistance in unimanual or bimanual conditions may be connected to the need for studies that elaborate on the mechanisms behind the bilateral training interventions, including the hand dominance, before working on brand new devices for clinical rehabilitation. Addressing this issue, some authors have implemented motor learning paradigms in bimanual environment, using robotic systems to study adaptation due to force field [ 21 , 31 , 32 , 33 ], proposing bimanual versions of the serial reaction time task [ 34 , 35 , 36 , 37 ], or investigating motor acuity by analysing the prehension force during bimanual manipulation [ 38 , 39 ].…”

“…Force recordings during bimanual manipulation are important to quantitatively analyse the coordination control among limbs, in stroke survivors [ 40 , 41 , 42 ] or healthy and elderly adults [ 39 , 43 , 44 , 45 , 46 ]. Additionally, a recent literature review with meta-analysis showed that patients with stroke have dynamic imparement control of bimanual coordination [ 30 ].…”