One of the crueler mind experiments was conducted by psychologist Harry Harlow who studied severe maternal deprivation. He separated a baby monkey from its mother and raised it in a cage with two substitute mothers. One mother was made from wire and had a bottle. The other mother was made from cloth, but didn't have a bottle. As soon the infant finished nursing, it would cling to the cloth monkey. When the experimenters introduced frightening stimulus into the cage, the monkeys ran to the cloth monkey for protection. The monkeys grew up with severe emotional and behavioral problems.