Measuring just noticeable differences for haptic force feedback: implications for rehabilitation

Describes preliminary work in the use of a virtual environment to derive just noticeable differences (JNDs) for force. Specifically, we look for thresholds of force sensitivity so that we may ultimately construct therapeutic force feedback distortions that stay below these thresholds. Initially, we have concentrated on JNDs as they are applied to the index finger; preliminary data in healthy individuals shows an average JND of approximately 100%. More significantly, the data indicate that visual feedback distortions in a virtual environment can be created to encourage increased force productions by up to 100%, and that this can be done without a patient's awareness.