Digital implementations of control laws typically involve discretization with respect to both time and space, and a control law that can achieve a task at coarser levels of discretization can be said to require less control attention, and also reduced implementation costs. One means of quantitatively capturing the attention of a control law is to measure the rate of change of the control with respect to changes in state and time. In this paper we present an attention-minimizing control law for ball catching and other target tracking tasks based on Brockett's attention criterion. We first highlight the connections between this attention criterion and some well-known principles from human motor control. Under the assumption that the optimal control law is the sum of a linear time-varying feedback term and a time-varying feedforward term, we derive an LQR-based minimum attention tracking control law that is stable, and obtained efficiently via a finite-dimensional optimization over the symmetric positive-definite matrices. Taking ball catching as our primary task, we perform numerical experiments comparing the performance of the various control strategies examined in the paper. Consistent with prevailing theories about human ball catching, our results exhibit several familiar features, e.g., the transition from open-loop to closed-loop control during the catching movement, and improved robustness to spatiotemporal discretization. The presented control laws are applicable to more general tracking problems that are subject to limited communication resources.
Central cord syndrome (CCS) is extremely rare as a direct consequence of generalized epileptic seizure. CCS is associated with hyperextension of the spinal cord and has characteristic radiologic findings including posterior ligamentous injury and prevertebral hyperintensity following magnetic resonance imaging (MRI). We experienced the case of a 25-year-old man who suffered CCS after status epilepticus. Cervical spinal MRI revealed high signal intensity at the C1 level but with no signal or structural changes in other sites. After rehabilitation management, the patient significantly improved on the ASIA (American Spinal Injury Association) motor scale and bladder function. We proposed that epilepsy related CCS may be caused by muscle contractions during generalized seizure, which can induce traction injury of the spinal cord or relative narrowing of spinal canal via transient herniated nucleus pulposus or transient subluxation of vertebra. We also suggest CCS without radiologic findings of trauma has good prognosis compared with other CCS.
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