Puppy Transition Period: Days 11-21

During the puppy transiton period, about the 3rd week of life, puppies eyes and ears begin to function so that vision and hearing develop. The more novelty that pups are exposed to during this time, the more capacity they have all their lives to accept as nontreatening, various sights and sounds.
After hearing develops, pups can be exposed to potentially frightening sounds in such a way that they are desensitized to them rather than frightened by them.

As sight develops, pups should be exposed to different shapes and lines, including lines that are horizontal & vertical  The pup's visual cortex needs this stimulus in order to develop capacity to see things that are vertical and horizontal. If a pup’s eyes are covered up during this transiton period, some vision cells never develop and the pup will lack the ability to perceive objects we take for granted, such as stairs and chair legs.