Babies tethered to contraptions can teach us about agency

Babies hooked up to airborne mobiles can tell us a lot about human agency, according to US researchers.

In a study published in PNAS, the researchers say they’ve captured the “origins of agency” on tape with 3-4-month-old infants.

The researchers used the “Mobile Conjugate Reinforcement” experiment: an experiment which has been used to test infants since the 1960s. Babies are put in a crib underneath a mobile, with their feet connected to a ribbon. Depending on where the ribbon is tethered, babies kicking may or may not make the mobile move.

The experimental design. Credit: Florida Atlantic University

“Positive feedback amplifies and highlights the cause-and-effect relationship between infant and mobile motion,” says senior author Professor J.A. Scott Kelso, a researcher at Florida Atlantic University, US.

“At some critical level of coordination, the infant recognises its causal powers and transitions from spontaneous to intentional behaviour. This aha! moment is marked by an abrupt increase in infant movement rate.”

Various formats of this experiment have been used to understand baby cognition, with researchers gathering data by tracking how frequently the babies kick.

This study of 16 infants goes deeper, focussing not just on baby movement but mobile movement as well. This approach, claim the researchers, frames agency as coming from both the organism and the environment it’s in.

Baby and 3d motion capture of baby
A 3D reconstruction/representation of the positions of the infant’s joints (red = left side; green = right side; yellow/orange = center; and the mobile’s position = blue). The image to the right depicts little silver spheres placed on the baby’s skin at different joints. Special cameras send out infrared light, which bounces off the spheres and reflects back to the cameras. The system then takes that reflective infrared information from all the cameras and figures out the exact location of each sphere. Credit: Florida Atlantic University

The researchers attached sensors to the infants and the rotating mobile above them, comparing motions through four different phases: (1) no mobile movement, (2) mobile moving independent of baby, (3) baby kicking triggering mobile movement, and (4) no mobile movement again.

The researchers found some things they expected – such as babies tended to move both feet equally when they weren’t controlling the mobile, but they moved the ribboned foot much more when they were controlling it.

But they also found that the babies’ pausing was significant.

“Our findings demonstrate that it’s not just the infants’ active movements that matter,” says co-author Professor Nancy Jones, also at Florida Atlantic University.

“That the mobile moves when the baby moves but not when the baby pauses—like Cezanne’s pauses between brush strokes—confirms to the baby that ‘I can make things happen.’,” write the researchers in their paper.

They also found that infants moved differently from each other, suggesting that behavioural “phenotypes” exist when it comes to agency. This could be used to spot infants “at risk”, according to the researchers.

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