The reason lies within the eye. In the eye are light receptors called cones and rods. Cones help us distinguish different colors, while rods help us see in dim light. The number of cones and rods is different for dogs. Turns out, dogs have fewer cone receptors than humans, which means they can't see as many colors. Human cones can detect 3 colors: red, green, and blue. Dog cones can only detect 2 colors. No one is certain what those 2 colors are. Some experts think it could be blue and yellow. Alexandra Horowitz, author of "Being a Dog" told us that it's difficult to know exactly what colors a dog sees, but it's probably similar to what we see at dusk. Dog eyes have more rods than humans, which means they can see much better at night. Dogs also have a layer of eye tissue that humans lack called the tapetum lucidum, it reflects light into the retina. This boosts dogs' night vision even more and is why dogs' eyes shine in the dark. Turns out, dogs' eyes see much more than just black and white. Consider that the next time you stare into those cute puppy dog eyes.
The theory has been around for some time, but a new book backs up the idea that 'dogs smell time’. “As each day wears a new smell, its hours mark changes in odors that your dog can notice,” explains Professor Alexandra Horowitz, founder of Barnard College's Dog Cognition Lab. The dog expert makes the claim in her new book 'Being A Dog'. While for most humans, the world is primarily visual, for dogs, their world is based on scents. Dogs are often used to sniff out drugs, explosives, disaster victims, dead bodies and even cancers, thanks to their extraordinary power of smell. Even for humans, scents can give clues as to what time of day it is, such as the smell of freshly brewed coffee in the morning. Professor Horowitz believes that dogs can detect subtle changes in scent during the day, giving them a sense of time. “Smells in a room change as the day goes on. Hot air rises, and it usually rises in currents along the walls and will rise to the ceiling and go kind of to the center of the room and drop,” she explains in an interview with Fresh Air. “I think dogs can smell that through the air movement in a room” she said. This could explain why a dog knows when its owner is due to return home. If the dog is able to detect the level of its owner's diminishing scent since they left the house, they may be able to predict roughly when they are due to come back.
