Alternate inter-digit finger tapping pattern resembles rudimentary finger grasping pattern

Neurotraumas often result in loss of finger grasping ability, thereby deteriorating quality of life. To develop effective rehabilitation method for finger grasping, objective evaluation metrics of grasping capability is a basic requirement. However, current evaluation methods for grasping confront challenges with their non-rhythmic nature and limited sample size, resulting in low statistical power and high variability. Finger tapping may shed light on this issue, based on its rhythmic nature and a common underlying mechanism between rhythmic finger tapping and rudimentary finger grasping. In this study, we investigated “phase difference” at inter-digit finger tapping, which indicates a deviation from the temporal symmetry of inter-digit tapping and potentially reflects a rudimentary finger grasping pattern. This was accomplished by analysing the metacarpophalangeal (MCP) angle of subjects’ fingers, measured by an infrared hand-motion sensor, during finger-tapping tasks. Subjects performed alternate or simultaneous rhythmic tapping tasks between two adjacent fingers among the thumb, index, and middle fingers while the MCP angle for the fingers was measured. Using the oscillating nature of the MCP angles for each finger, we established phase difference as a metric to describe relative interdigital motion. We identified congruency in phase difference between the alternate inter-digit tapping pattern and the rudimentary grasping pattern. Experimental results with phase analysis suggest that alternate inter-digit tapping, which is a rhythmic and intuitive task, is strongly correlated with the rudimentary grasping in kinematics, while the simultaneous tapping is not. Accordingly, we predict potential applications of alternate inter-digit finger tapping and its metrics in grasping diagnostics and rehabilitation monitoring.