The experiment is by Margaret S. Livingstone, Harvard Medical School. It involves mother macaques that have lost their young. It shows that they form strong and lasting attachments to soft inanimate objects. This is the stuffed baby experiment. Appears in ‘Proceedings of the National Academy of Science’ (PNAS).
It all started with an 8-year-old female rhesus named Ve. Her calf was stillborn. When the small carcass was removed, she showed signs of great distress. She vocalized loudly and looked around the enclosure for something. Other monkeys housed in the same place also became agitated. The researcher placed a dummy, a soft, furry mouse, in the room. The female picked up the stuffed animal immediately and held it against her chest. She stopped squealing and calmed down.

Attachment to stuffed animals
She carried the stuffed animal on her for over a week, with no signs of distress. About ten days after the failed delivery she discarded the stuffed animal with no problems. A year later she gave birth and successfully raised a second baby.
In all, Livingstone offered stuffed animals to five different females. It was just after eight births that the pups were removed. Three of them carried the toy from about a week to several months. The females preferred to ‘adopt’ soft toys rather than rigid ones of similar sizes.
One of the monkeys was wanted to return her cub alive six hours after birth. But she ignored it. Her attachment to the doll was already greater than her attraction to her own child.

Soothing
The maternal attachment drive can be satisfied by holding a soft inanimate object. “The calming effect of the toy on the monkey was enormous. Using such surrogates may be a useful technique for relieving the stress associated with infant death. Or infant withdrawal in captive primates,” he notes.
The stuffed baby experiment opens up other questions. How much of this can be extrapolated to the human experience? That remains a long way to be determined. For now, it will serve to ease the anxiety of mother macaques.