Quantitative Assessment of Functional Object Interactions After Stroke

Many individuals after stroke exhibit upper extremity (UE) motor impairments. Manual interactions with objects are ubiquitous in everyday life and impaired interactive abilities result in loss of independence. Hence, understanding how deficits of UE manifest in functional interactions with objects is important for neurorehabilitation. However, detailed quantitative measurements of such intricate skills have been elusive so that current quantification of motor impairment has focused on impairment. This paper introduces a portable, low-cost device custom-designed (MAGIC Table) to record real-time kinematics of a functional skill, the transport of a complex object, i.e., a ‘cup of coffee’, on a table surface. Participants move a 3D-printed cup with a rolling ball inside, representing the sloshing coffee. Three participants after stroke and three able-bodied participants performed a planar elbow flexion-extension movement while holding the cup without losing the ball. Performance recorded via a webcam mounted above the table, was evaluated with both conventional metrics, i.e., movement time and smoothness, and novel kinematic metrics, i.e., risk and predictability, derived in previous theoretical research on the same task. Movement time and smoothness were less sensitive to functional ability than risk and predictability. Able-bodied participants engaged in more risky strategies, but also prioritized predictability of object dynamics. The stroke survivors were risk averse and had less predictable interactions. These results showed the feasibility of the new device and promise that the new theory-based analyses can be leveraged for novel insights into functional skill after stroke.