Evaluating angular accuracy of wrist-based haptic directional guidance for hand movement

Haptic guidance for the hand can offer an alternative to visual or audio feedback when those information channels are overloaded or inaccessible due to environmental factors, vision impairments, or hearing loss. We report on a controlled lab experiment to evaluate the impact of directional wrist-based vibro-motor feedback on hand movement, comparing lower-fidelity (4-motor) and higher-fidelity (8-motor) wristbands. Twenty blindfolded participants completed a series of trials, which consisted of interpreting a haptic stimulus and executing a 2D directional movement on a touchscreen. We compare the two conditions in terms of movement error and trial speed, but also analyze the impact of specific directions on performance. Our results show that doubling the number of haptic motors reduces directional movement error but not to the extent expected. We also empirically derive an apparent lower bound in accuracy of ∼25° in interpreting and executing on the directional haptic signal.