The effect of vision on tactile TOJ during arm crossing

When people cross their arms, subjective rank ordering of successive unseen tactile stimuli delivered to both arms is affected (often being reversed) (Shore et al., 2002; Yamamoto and Kitazawa, 2001). It is also known that vision plays a significant role in modulating perceived limb position (Graziano et al., 2000). In this study, we examined the effect of vision; i.e., eyes opening and closing on tactile temporal order judgment (TOJ) with their arms crossed or uncrossed. In a psychophysical experiment, participants ( n = 18 , 13 males, 27.3 ± 1.8 y.o.) were required to judge temporal order of two tactile stimuli that were delivered to their both ring fingers with four conditions: uncrossed arms with eyes closed, crossed arms with eyes closed, uncrossed arms with eyes open and crossed arms with eyes open. To evaluate judgment probabilities of the participants, degree of reversals of their judgment was calculated as the sum of differences between correct response rates of the arms crossed condition and those of the arms uncrossed condition. In arms uncrossed conditions, judgment probabilities of the participants were not significantly different between eyes closed and open conditions. In contrast, reversal of the judgment with eyes closed was significantly larger than that with eyes open in arms crossed conditions ( p < 0 . 05 ). The results suggest that vision play a significant role in tactile order judgment when the subject arms crossed.