Reversal of subjective temporal order due to sensory and motor integrations

It is generally accepted that the brain can resolve the order of two stimuli that are separated in time by 20-50 ms. This applies to temporal order judgment of two tactile stimuli, delivered one to each hand, as long as the arms are uncrossed. However, crossing the arms caused misreporting (that is, inverting) of the temporal order. The reversal was not due to simple confusion of hands, because correct judgment was recovered at longer intervals (e.g., 1.5 s). When the stimuli were delivered to the tips of sticks held in each hand, the judgment was altered by crossing the sticks without changing the spatial locations of the hands. We recently found that temporal order judgments of tactile stimuli are sometimes reversed by visual distractors and by saccadic eye movements. The results suggest that tactile stimuli are ordered in time only after they are referred to relevant locations in space, where multisensory (visual, tactile and proprioceptive) and motor (saccade-related) signals converge. Results from functional imaging generally support this idea. Because performance of congenitally blind people in tactile temporal order judgment is much superior to the sighted and is never impaired by crossing the arms (Roeder et al., 2004), we finally suggest that our integrity of multisensory signals in space is only achieved at the cost of continuity in time.