"a dog must be 20 feet away from an object to clearly visualize details of that object that a human with normal vision could clearly visualize from a distance of 75 feet." My dogs are the same way... I think it has to do with species distinction... A bird is a bird... But different people hold different meanings for them... So even though they know you're a person, they wait 'til you get closer to make judgment.
psychlops.psy.uconn.edu (All you ever wanted to know)
psychlops.psy.uconn.edu (All you ever wanted to know)