Light adaptation for visual pattern recognition in flies.

Abstract Flies were found to possess the light adaptation phenomena of vertebrates whereby the eyes achieve optimal sensitivity to an intensity increment on a given background illumination. This was found in the photoreceptors and several higher levels including a behavioral response. It has a time constant varying directly with the sudden change of background intensity that ranges up to about 20 sec for large changes in background. This was distinguished from another adaptation phenomena of about 6 min duration, part of which appears to be due to a change in ommatidial fields produced by shielding pigment migration effects.