Tracker and Recognizer Schematic. A. Tracker. A Petri plate with worm is placed on a computer-controlled motorized stage. A joystick is used to center the worm in the field of view. The worm is recorded on VCR. B. Recognizer. The video tape is played into a computer by a computer-controlled VCR to recognize the worm and record its body posture and position as a function of time.