Finger-thumb coordination is crucial to interacting with our environment. This coordination remains incompletely understood, even in neurologically intact individuals, and is difficult to study with current interface devices. Knowledge of finger-thumb relationships during dynamic movement facilitate identification of key impairment mechanisms following stroke and thus, help to guide rehabilitation strategies. Accordingly, a high-bandwidth, biocompatible finger exoskeleton is developed and implemented in a pilot study to investigate coupling between the finger and thumb during pinching movements. Performance of the Cable Actuated Finger Exoskeleton (CAFE) is analyzed in the lab and during interaction with human subjects, both neurologically intact and survivors of stroke. The exoskeleton is found to perform exceedingly well, exceeding nearly all design requirements lending to the continued use of the CAFE a research platform for human motor control of the hand.

During experimental trials, participants move through index finger and thumb palmar pinching movements while the CAFE delivers perturbations during the closing and opening phases of movement. Two experiments are conducted, delivering reflex-inducing or joint-locking perturbations to the index finger. Muscle EMG and thumb tip trajectory are recorded during movement and variations in these parameters immediately following perturbation demonstrate the effect of coupling of the index finger and thumb. Reflexive coupling is evidenced in both healthy and post-stroke individuals by heteronymous reflexes in the unstretched muscles of the thumb. Similarly, kinematic changes are apparent in thumb movement following impedance perturbations of the index finger in both populations. Coupling is observed to vary with phase of movement in intact participants, but not following stroke, suggesting a loss of modulation following stroke. Most notably: in survivors of stroke impedance perturbations to the index finger during the opening phase of movement results in dramatically increased thumb opening.