The Effect of Rhythmic Tactile Stimuli Under the Voluntary Movement on Audio-Tactile Temporal Order Judgement.

The simultaneous perception of multimodal sensory information is important for effective reactions to the external environment. In relation to the effect on time perception, voluntary movement and rhythmic stimuli have already been identified in previous studies to be associated with improved accuracy of temporal order judgments (TOJs). Here, we examined whether the combination of voluntary movement and rhythmic stimuli improves the just noticeable difference (JND) in audio-tactile TOJ Tasks. Four different experimental conditions were studied, involving two types of movements (voluntary movement, involuntary movement) and two types of stimulus presentation (rhythmic, one-time only). In the voluntary movement condition (VM), after the auditory stimulus (cue sound) participants moved their right index finger voluntarily and naturally, while in the involuntary movement condition (IM), their right index finger was moved by the tactile device. The stimuli were provided in a rhythmic or one-time only manner by hitting inside the first joint of the participants' right index finger using a tactile device. Furthermore, in the rhythmical tactile (RT) conditions, tactile stimuli were presented rhythmically to the right index finger 5 times consecutively. On the other hand, in the one-time tactile (1T) conditions, tactile stimuli was presented one-time only to the right index finger. Participants made an order judgment for the fifth tactile stimuli and the first and only auditory stimuli. In our TOJ tasks, auditory-tactile stimulus pairs were presented to participants with varying stimulus-onset asynchronies (SOAs; intervals between the within-pair onsets of the auditory and tactile stimuli). For the two stimuli presented at a time that were shifted by the SOA, the participants were asked to judge which one was presented first, and they were given a two-choice answer. Using a non-parametric test, our results showed that voluntary movement and rhythmic tactile stimuli were both effective in improving the JNDs in TOJ Tasks. However, in the combination of voluntary movement and rhythmic tactile stimuli, we found that there was no significant difference in JNDs in our experiments.