section_path: Anatomy and physiology/Senses
section_name: Senses
paragraph_text: Senses
  
  Dogs' senses include vision, hearing, smell, taste, touch, and magnetoreception. One study suggests that dogs can feel small variations in Earth's magnetic field. Dogs prefer to defecate with their spines aligned in a north-south position in calm magnetic field conditions.
  
  Dogs' vision is dichromatic; the dog's visual world consists of yellows, blues, and grays. They have difficulty differentiating between red and green. The divergence of the eye axis of dogs ranges from 12–25°, depending on the breed. Dogs' eyes of different breeds can have different retina configurations. The fovea centralis area of dogs' eyes, which is attached to a nerve fiber, is the most sensitive to photons.
  
  While the human brain is dominated by a large visual cortex, the dog brain is dominated by a large olfactory cortex. Dogs have roughly forty times more smell-sensitive receptors than humans, ranging from about 125 million to nearly 300 million in some dog breeds, such as bloodhounds. This sense of smell is the most prominent sense of the species; it detects chemical changes in the environment, allowing dogs to pinpoint the location of mating partners, potential stressors, resources, etc. Dogs also have an acute sense of hearing up to 4 times greater than that of humans. They can pick up the slightest sounds from about 400 m (1,300 ft) compared to 90 m (300 ft) for humans.
  
  Dogs have specialized whiskers known as vibrissae, sensing organs present above the dog's eyes, below their jaw, and on their muzzle. Vibrissae are more rigid, embedded much more deeply in the skin than other hairs, and have a greater number of receptor cells at their base. They can detect air currents, subtle vibrations, and objects in the dark. They provide an early warning system for objects that might strike the face or eyes, and probably help direct food and objects towards the mouth.