Abstract-There are many algorithms for calculating derivatives. The two-point central difference algorithm is the simplest. Besides simplicity, the two most important characteristics of this algorithm are accuracy and frequency response. The frequency content of the data prescribes a lower limit on the sampling rate. The smoothness and accuracy of the data determine the optimal step size. We discuss the low-pass filter characteristics of this algorithm and derive the optimal step size for two types of human eye movement data. To calculate the velocity of fast (saccadic) eye movements, the algorithm should have a cutoff frequency of 74 Hz. For typical slow (smooth pursuit) eye movements, a step size of 25 or 50 ms is optimal,
Abstract. Humans can overcome the 150 ms time delay of the smooth pursuit eye movement system and track smoothly moving visual targets with zero-latency. Our target-selective adaptive control model can also overcome an inherent time delay and produce zero-latency tracking. No other model or man-made system can do this. Our model is physically realizable and physiologically realistic. The technique used in our model should be useful for analyzing other time-delay systems, such as man-machine systems and robots.
Abstract-When a person walks the head undergoes horizontal and vertical rotations, and also horizontal and vertical translations. To visually fixate on an object while walking, compensatory horizontal and vertical eye movements must be made. Our model for this gaze (head plus eye) control system includes three types of eye movements: smooth pursuit, saccadic, and vestibulo-ocular. The smooth pursuit system uses a target-selective adaptive controller (TSAC) that compensates for the large inherent time delay and produces zero-latency tracking of predictable targets. Target movements were selected to minimize the role of the saccadic control system. Typical tracking is shown while seated with the head restrained, standing with unrestrained head, performing voluntary head rotations, and walking. Each additional degree of freedom produced additional head movements that were compensated by additional eye movements. It is shown that while a human walks the effects of head rotations (yaw) cancel the effects of head translations, thus minimizing the resulting horizontal eye rotations necessary to maintain fixation.
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