Abstract: The recogntion of repetitive movements characteristic of walking people, galloping horses, or flying birds is a routine function of the human visual system. It has been demonstrated that humans can recognize such activity solely on the basis of motion information. We present a novel computational approach for detecting such activities on the basis of the periodic nature of their signatures. The appraoch suggests a low-level feature-based activity recognition mechanism. this contrasts with earlier, model-based approaches for recognizing such activities.