Follow your nose

How dogs may perceive scent

source: New Scientist vol 211 no 2826, August 20 2011 starts p36, 2 pages long

Dogs may experience strong smells in a different way from humans, perceiving them as layers, with different sorts of information. Alexandra Horowitz of Columbia University, New York, sees dogs as able to perceive scent in a complex way, rather than as mono-smells. Dogs use visual cues as back-ups. Police tracker dogs rely on their noses, ignoring the visual cue of footprints. Just one object may offer different sorts of information, according to Horowitz. Dogs may sense the time that has passed since smells were left, so have a sense of time. Dogs' nostrils are far enough apart for them to smell from different regions and work out the direction of a smell. Dogs have 300 million olfactory receptors. Humans have six million. The olfactory cortex of dogs accounts for 12.5% of total brain mass, but in humans it is only 1%.