Do you ever worry about being out on the trail after dark? It's a legitimate concern; after all, if humans can't see well in low light, how well can a horse?
Researchers already know that horses have the physical equipment for scotopic (night) vision, with more rods than cones and a reflective structure in the retina. Experience tells us that they continue to graze, interact, and move about at night. Wild mustangs can even be seen running at full gallop over rough terrain while negotiating sagebrush, rocks, hills, and gullies with only starlight to guide them.
Bodie, a Paint/draft cross, correctly chooses the black circle instead of the triangle. (Note: this photo was taken in full light for enhanced photo quality, but all testing for scotopic vision was carried out in low-light conditions.)
Even so, the physics of the reflective structure could actually make it more difficult for horses to discriminate objects in dim light. As a result, humans have remained mostly “in the dark” about just how well our equine friends can differentiate shapes and objects in dimly lit settings. However, recent research at the Equine Research Foundation (ERF) in California, led by Evelyn B. Hanggi, MS, PhD, assisted by program director Jerry Ingersoll, is now shedding new light on this old question.
Through a series of positive-reinforcement tests with four horses in progressively darker situations, the ERF investigators di