Hastad, O. and Odeen A. (2008). Different Ranking of Avian Colors Predicted by Modeling of Retinal Function in Humans and Birds. American Naturalist, 171: 831-838

It has only been recently that visual studies were based on neurological findings, so much of the knowledge in the field of light reception has been gathered using the human eye. To quantify the discrepancy between avian and human light reception, Hastad and Odeen (2008) used mathematical models to compare the levels of contrast birds and humans would see in avian feather patterns.

To compare the interpretation of feather patterns between species, Hastad and Odeen first scanned patterns from 67 species of birds with a spectrophotometer. Their selection included birds that have the opsin for ultraviolet light and those that did not. These scanned samples were then run through a modeling program which predicted the levels of contrast that a UV sensitive bird, a non-UV sensitive bird and a human would see.

The researchers found that the human eye rarely saw contrast levels similar to what the bird saw, and in roughly 40% of cases differed from the birds on which color patterns produced the highest levels of contrast. Interestingly, these variations were upheld even if UV light was removed from the model. Because of these results, it was concluded that the human eye is insufficient to judge coloration in birds.

This study relates most closely to the lecture from 2/26. It discusses the differences in light signal reception due to different opsin types, numbers and their absorptions relative to each other. The opsin proteins in birds are more evenly spaced in their absorption of light, as opposed to the human photoreceptors which nearly overlap on the longer wavelengths. This article reinforces the distinctions made between different photosystems in animals based on the mechanics of the system.