Brightness discrimination ability in the West Indian manatee (Trichechus manatus)

Two manatees were tested on their ability to discriminate brightness using a series of 30 shades of grey varying from white to black. The animals were trained to discriminate between different shades of grey in a twofold simultaneous-choice situation. Their ability to discern brightness differences correlates with Werber's law, and the calculated Werber fraction is 0.35.