Early visual processing in insects.

The present account reviews some of the progress made recently towards understanding better the processing of visual information in the peripheral visual system of insects. To limit the scope, it concentrates mainly upon the group that has been the subject of the most intensive recent work, and that is better understood from most aspects: the Diptera, or true flies. The region discussed is the retina proper and first synaptic neuropile, the lamina, and thus encompasses visual processing up to the level of third-order visual neurones. A number of reviews give either wider or fuller accounts of the same area: those of Laughlin (1980) and Jarvilehto (1984) are particularly wideranging, Shaw (1981) discusses the neural connections in detail, whilst Meinertzhagen & Frohlich (1983) and Meinertzhagen (1984) provide introductions to aspects of neural development. A recent NATO conference volume features this area (Ali, 1984). Much of the recent advance in knowledge has come from detailed application of electron-microscopic (EM) methods to the anatomy of the neuropile. To illuminate the function of the microanatomical circuits, the optics and general layout of the eye are first reviewed briefly; several recent accounts of this heavily researched area may be consulted for more detail, for instance Kirschfeld (1976), Stavenga (1979), Land (1980) and Ali (1984).