Metric analysis of threshold spectral sensitivity in the honeybee.

Behavioral spectral sensitivity curves are frequently used to characterize peripheral stages of visual processing. We test specific hypotheses about the physiology underlying honeybee spectral sensitivity by approximating published sensitivity curves with several metric models. The analysis shows that: (1) models assuming no interactions between different receptor types do not explain the behavioral data. Similarly, neither simple luminance mechanism models (sum of receptor excitations), nor models in which only the most sensitive receptor determines sensitivity fit the data. (2) The minimum number of postreceptoral mechanisms mediating discrimination is two. (3) Both mechanisms are of the chromatic type. Adding an achromatic mechanism decreases the accuracy of approximation.