At universities in the 1950s, 100s of babies were loaned from orphanages. Students could then practice the latest child-rearing theories on live objects.
The Monster Study
Within a group of children, negative reinforcement was used on those who stuttered & praise on those who didn’t. All the children ended up developing stutters.
An 11 month infant was given various objects. A hammer was banged next to his head whenever he interacted with the objects conditioning him to be terrified of them.
The Visual Cliff
Babies were placed above an illusion of a sheer drop their mothers tried to coax them to crawl over the ‘cliff’ and it was concluded that babies shouldn’t be left near high edges.