The effect of voluntary movement on audio-haptic temporal order judgment: A fundamental study for timing control in human-machine interaction

In this study, we investigated the effect of active/ passive motion on audio-haptic temporal order judgment. We used a psychophysical method to measure the differences in Point of Subjective Simultaneity (PSS) and Just Noticeable Difference (JND). PSS and JND were measured under "Voluntary" condition, "Involuntary" condition, and "No-movement" condition. Except Voluntary condition, when the haptic stimulus was presented before the auditory stimulus, the two stimuli were more likely to be perceived as simultaneous. PSS and JND of Voluntary condition were relatively smaller than those of Involuntary and No-movement conditions. Each PSS and JND under Involuntary condition was not significantly different from under No-movement condition. These results suggest that the proprioceptive information and the efference copy in voluntary motion accelerates haptic perception and improves the resolution of temporal order judgment for audio-haptic stimulus, while the proprioceptive information alone does not achieve significant effect on the judgment in involuntary motion.