Coordination of human grasp and manipulation forces - PROJECT SUMMARY
The hand’s sophisticated neuromuscular system enables us to interact with the world in a myriad of ways,
one of which is dexterous manipulation. The hand’s incredible versatility, however, comes at a cost: when
peripheral neuropathies, neurological disorders or traumatic injury occur, our ability to improve sensorimotor
function is severely challenged by our limited understanding of the hand’s sensorimotor control mechanisms.
Therefore, improving our understanding of these mechanisms could enhance the impact of clinical intervention.
This notion has driven extensive research over the past four decades aiming at unravelling how the hand’s
sensorimotor control mechanisms operate. Previous research has provided significant insights into the
coordination of digit forces required to prevent object slip. Surprisingly, however, this previous work neglected
to address another important component of manipulation: the ability to control object position and orientation,
i.e., pose. This is a critical gap because dexterous manipulation often requires both object slip prevention and
dexterous control of object pose. To address this gap, in the past decade our laboratory has developed an
experimental paradigm that allows subjects to choose where to grasp the object and contains a dexterity
component, i.e., lifting an object straight while preventing it from tilting. Nevertheless, the major limitation of
this work is that the modulation of load and grip forces cannot be decoupled to identify their relative contribution
to object slip prevention and pose control. To fill this gap, we propose an approach that will allow us, for the
first time, to identify the control mechanisms underlying grasp and manipulation. Our approach combines a
task with a dexterity component, surface electromyography of digit muscles, and a novel application of digit
force analysis developed for robotic manipulation. Our task requires subjects to coordinate digit forces to
simultaneously prevent object slip and minimize object tilt. Our analysis can mathematically decouple digit
forces into grasp force (object slip prevention) and manipulation force (object pose control). We will pursue two
aims: (1) To determine the causal relation between grasp and manipulation forces, and (2) To quantify the
effect of predictability of object properties on the coordination between grasp and manipulation forces. If
successful, this new knowledge will enable clinicians to extract information about the state of the hand’s
sensorimotor function that cannot otherwise be extracted by clinical assessment tools. Our long-term objective
is to improve the theoretical constructs of dexterous manipulation control and their translation to clinical
applications, including tools for quantifying recovery of hand function following clinical intervention, as well as
design of assistive and/or rehabilitation devices.
