Our ability to pick out objects from their backgrounds based on differences in luminance has traditionally been thought to remain constant across different light intensities. 

This assumption has been based largely on previous studies using relatively dim stimuli (Geisler et al, 2007). But researchers at the State University of New York set out to investigate how contrast sensitivity is affected in a greater range of light intensities.

In tests on cats and humans, the group measured the responses of neurons to different combinations of contrast and light intensities.