Intermittent Brain Motor Control Observed in Continuous Tracking Task
In the present study, the author analyzed the hand movement in one-dimensional visuo-manual tracking task. When the target moved slowly or unpredictably, the hand velocity contained many bell-shaped components lasting several-hundred milliseconds. When th
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Abstract In the present study, the author analyzed the hand movement in one-dimensional visuo-manual tracking task. When the target moved slowly or unpredictably, the hand velocity contained many bell-shaped components lasting several-hundred milliseconds. When the target moved fast and sinusoidally, on the other hand, subjects seemed to adjust the movement by a unit of cycle. These findings suggest that our brain divides temporal axis into discrete segments and plans/adjusts motor commands for each segment. This “intermittent motor control” may be the brain’s fundamental strategy for achieving good motor performance with slow sensorimotor system.
1 Introduction Brain motor control system contains many delay/lag elements in the control loop, such as neural transmission, neural calculation and muscle activation. A fundamental question here is how our brain performs a given motor task in a real-time fashion with such a slow system. Computational theory gave an answer of “feed-forward control,” that is, our brain makes a motor plan in advance and executes it without sensory feedback. The validity of this framework has been discussed mainly in relation to reaching movement. Meanwhile, the requirement of real-time control must be more serious in performing a continuous task (such as tracking) compared to a ballistic task (such as reaching), because brain has to obtain task-related sensory information, to design/adjust motor plans and to monitor the performance in a seamless manner. How does our brain handle this situation? One possible answer
Y. Sakaguchi () Human Informatics Laboratory, Graduate School of Information Systems, University of Electro-Communications, Tokyo 182-8585, Japan e-mail: [email protected] Y. Yamaguchi (ed.), Advances in Cognitive Neurodynamics (III), DOI 10.1007/978-94-007-4792-0 62, © Springer ScienceCBusiness Media Dordrecht 2013
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is that brain divides the time axis into discrete segments and executes feed-forward control in each time segment (i.e., “intermittent control”). Actually, our body movement contains discontinuous components even in a continuous tracking task [1–3]. The present study investigates the nature of such discontinuities in a visuomanual tracking task. Especially, the author aims to analyze the hand movement in time domain while most previous analyses were done in frequency domain.
2 Method The experimental setup was as follows. A subject sat in front of a table with his/her chin rested on a chin rest. He/she put his/her right hand on an air-floating slider moving along a linear rail in a front-back direction. The position of the slider was monitored by an optical sensor and sampled by 200 Hz. The hand position was displayed as the vertical position of a red laser spot on a front screen (2.2 m apart from the subject head), where forward hand motion brought upward spot motion. Hand motion was magnified two times on the screen (i.e., 10 mm hand move brought 20 mm (or 0.5ı in visual angle) spot move). On the screen, another green laser spot (“ta
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