An effect of minimum-jerk acceleration on arm velocity-change perception

Abstract

In recent years, the methods of motor learning using haptic devices have been studied, which give motion-related stimuli to learners so that they can perceive the stimuli with proprioception. In order to design control systems of the haptic devices, we need to understand the characteristics of human’s position, velocity, and force sensation. Then, in this study, we took up the velocity sensation with proprioception, and examined velocity JNDs (Just Noticeable Differences), which represent the smallest differences humans can discriminate, and are a representative feature on human velocity-change perception. In particular, we focused on an effect of acceleration during velocitychange on the human velocity-change perception. A representative way to change velocity is a constant-acceleration movement where acceleration is changed linearly with respect to time, however, it differs from human natural movements that smoothly accelerate/decelerate. Therefore, in this study, we employed the minimum-jerk trajectory that is referred to as a trajectory representing human natural movement. Then, we examined velocity the JNDs in correspondence with various magnitudes of acceleration. In an experiment, as a presenting process, we enforced subjects to accelerate their right hand with a minimumjerk trajectory from predetermined velocities to other predetermined velocities. We set acceleration-time durations to 1.0, 1.4, 2.2, 3.4, 5.0, and 7.0 s. After the acceleration movement, subjects answered whether they perceived velocity-change or not during the movement. The velocity JNDs were obtained by repeating the process under the PEST protocol with various velocity differences. As a result, it was found that, while the acceleration-time duration condition was decreased from the maximum of 7s to the minimum of 1s, and acceleration was approximately increased by 7 times, while, among velocity JND means, the maximum is just 1.4 times of the minimum. As a result, it was suggested that the magnitude of acceleration is not a determinative factor in perceiving velocity-changes caused by externally-applied forces under the minimum-jerk trajectory.