The alteration of simultaneity perception in the cross-modal integration under motor control

We investigated the effect of the efference copy and the proprioceptive feedback on auditory-tactile temporal order judgment, using Temporal Order Judgment (TOJ) task to measure the differences in Point of Subjective Simultaneity (PSS) and Just Noticeable Difference (JND). These parameters were measured under Voluntary condition, Involuntary condition, and No-movement condition. While both the Involuntary and Voluntary conditions contain proprioceptive feedback, only Voluntary condition contains efference copy. JND of Voluntary condition was smaller than that of No-movement condition. PSS was significantly different among the three conditions. Movement condition shifted PSS to the point where auditory stimulus presented prior to tactile stimulus compared to No-movement condition. Furthermore, the shift in PSS of Voluntary condition was larger than that of Involuntary condition. These results suggest that each proprioceptive information and efference copy accelerates tactile perception, and voluntary movement improves the resolution of TOJ for audio-tactile stimulus, while the proprioceptive information alone does not achieve significant effect of improvement on the judgment in involuntary motion.