Insect Compound Eyes: Design of Photoreceptor Arrays for Image Pre-processing

Insect eyes are constructed so that much of the destruction of irrelevant data and pre-processing of vital information is accomplished by the receptor array itself, reducing substantially the computational load placed on the neural system. One of the most important mechanisms for destruction of irrelevant data is coarse spatial sampling. At long range, spectral properties of objects then become particularly important as a source of signals conveying specific information about qualities of those objects. Colored wing patterns of butterflies provide important signals for recognition of species and sex, but little is known about butterfly color vision. This study analyzes data from optophysiological measurements of intact butterfly eyes. It demonstrates great diversity in absorbance spectra of visual pigments and spectral sensitivity functions of photoreceptors, and characterizes quantitatively those functions. Reflectance spectra of wing patches are measured microspectrophotometrically. Calculated quantum catches for photoreceptors viewing illuminated wing patches indicate which wing features have value as signals.