VISUAL TRACKING AND PURSUIT - HUMANS AND ARTHROPODS COMPARED

The control systems that different arthropods (praying mantids, hoverflies and the water-flea Polyphemus) use for visual tracking and pursuit of prey or conspecifics are compared with that of humans. The different control systems are also simulated computationally and their performances compared. The general conclusions are: (i) at low speeds or frequencies, continuous (smooth) tracking gives the best performance since it provides a good match to both the position and velocity of the target [humans, hoverflies]; (ii) the addition of velocity feedback to the position signal improves the performance of smooth systems, especially at higher frequencies [humans]; (iii) at higher frequencies position tracking is greatly improved by a switch to a sampled (saccadic) system [humans, hoverflies], especially when velocity as well as position errors are taken into account [mantids]; (iv) mixed systems in which position is dealt with by a saccadic system and velocity by a smooth system give the best overall results [humans and mantids in low contrast environments]; (v) in contrast to the others, the Polyphemus eye movement control system measures neither the position nor the velocity of the target, the direction and duration of constant velocity saccades depending only on the stimulus direction and the time the stimulus remains in a central zone of the eye.