Dynamical Systems Interpretation of Reversal of Subjective Temporal Order Due to Arm Crossing

Beginning with the famous conception of B. Libet, how the brain orders successive events has been a matter of intense debate in neuroscience. Yamamoto and Kitazawa (S. Yamamoto et al., 2001, Nature Neuroscience, 4, p.759) revealed that subjective temporal orders of successive taps to the hands are easily reversed simply by crossing the arms. What is astonishing, especially in the arm-crossing case, is that when the tapping interval was less than 0.3 seconds, the error rate grew to 100%. This result could be taken as default functionality of the real brain ’s adaptation process to its own body. In this presentation, we propose a model that interprets the cross hand effect of temporal order judgment from the dynamical systems perspective. According to the results revealed by Yamamoto and Kitazawa, and using a genetic algorithm, we reconstructed the cross hand effect with an agent containing a recurrent neural network. As a result, we found two important properties of the internal dynamics that enable this phenomenon. One is the enlarged response time delay to a single stimulus when the hands are crossed. According to the body posture, the agent changes the internal time unit to confront the successive stimuli.

And the second is the generation of the structure called the “stimulus sensitive time window” inside the enlarged response time delay. If the second stimulus is applied to this time region, inversion of judgment occurs. The results suggest that the body image is not statically determined but rather dynamically sustained. In the presentation, we will explain the detailed model description and the mechanism realizing those temporal properties. Finally, we will discuss the implication of this model for the embodied sensorimotor coupling system and future work.