This is what the AKC has to say:
What can a breeder do to properly socialize each pup? The starting point is for the litter to be raised within a home environment with frequent human contact, rather than secluded in the yard or a kennel. This is the first step in ensuring that the pups will be prepared for life in a household, with all the sounds, smells, and hustle-and-bustle that this entails.
Some breeders will move a litter from room to room on progressive weeks, to change the scene and familiarize the pups with such varied sounds as those of the dishwasher, television, and washer-dryer. Others like to situate the puppy pen near the home’s center of activity, so the pups are exposed to comings and goings and hear a variety of human voices. American Kennel Club - AKC eNewsletter