Behavioural evidence for parallel information processing in the visual system of insects.

Many flying insects display remarkable visual agility in capturing prey or pursuing a potential mate. They are capable of detecting, recognising, tracking and capturing a rapidly moving object on the wing. These manoeuvres are usually completed in a couple of seconds. The interval of time between the absorption of light quanta by the photoreceptors and the generation of an appropriate behavioural response is very short, encompassing only a few tens of milliseconds. In this time the visual nervous system has abstracted the essential features of the object, and recognized it (where appropriate), or measured its movement and computed an interception course. As an elementary unit of computation, we know that a neuron in the nervous system is considerably slower than, say, a flip-flop in the CPU of a modern computer. However, it is evident from the visual performance of an insect that the nervous system as a whole processes optical information much faster than a modern computer does. Rapid processing of visual information by animals therefore has to be attributed to the structure and the modus operandi of the nervous system.