We should expect that a horse’s experiences of the world are very different than ours. We know that dogs can hear ultrasound — sounds higher than the range of human hearing — and that elephants can hear infrasound — sounds lower than the range of human hearing. We have learned that bees and birds and butterflies see ultraviolet light, and that a male silkworm can detect a female over 6 miles away. We know that birds can fly by the stars, and can sense magnetic fields. And so we have reason to suspect big differences between horse sense and human sense.
Much of our species’ early development was in the trees, in heavy vegetation. Horses developed on the plains, in open habitat. Humans ate fruit, and needed color vision to determine what was ripe. Horses ate grass, and didn’t need red at all. Humans hunted, and needed to be able to focus on selected prey. Horses were adept at running away from predators, but had to spot them first, somewhere on a 360 degree horizon. Our sensory systems evolved to give us what we needed, with few luxuries. So we would expect that the vision, hearing, and smell of humans and horses might greatly differ.