Baby illusion! Mothers underestimate their youngest child's height by almost three inches, a new study has found.
Many parents say when their second child is born, their first child suddenly appears to have grown overnight.
Now, researchers have an explanation: until the birth of the new child, those parents were subject to a "baby illusion," routinely mis-perceiving their youngest child as smaller (and younger) than he or she really was.
"Contrary to what many may think, this isn't happening just because the older child just looks so big compared to a baby," said Jordy Kaufman of Swinburne University of Technology in Australia.
"It actually happens because all along the parents were under an illusion that their first child was smaller than he or she really was. When the new baby is born, the spell is broken and parents now see their older child as he or she really is," said Kaufman.
Kaufman and his colleagues made the discovery first by asking 747 mothers if they remembered experiencing a sudden shift in their first child's size after the birth of a new infant. The researchers found that 70 per cent of the mothers did.
To further explore that perceptual shift, the researchers asked mothers to estimate the height of one of their young children (aged 2 to 6) by marking a blank wall.
When the researchers compared those height estimations to the child's real height, they found something very interesting: mothers significantly underestimated the height of their youngest child by 7.5 cm or 3 inches on average. In contrast, height estimates for the eldest child were almost accurate.
"The key implication is that we may treat our youngest children as if they are actually younger than they really are," Kaufman said.
"In other words, our research potentially explains why the 'baby of the family' never outgrows that label. To the parents, the baby of the family may always be 'the baby.'" said Kaufman.
The findings are a useful reminder of just how filtered our own perceptions of the world around us can be.
"We cannot trust the accuracy of our perceptions," Kaufman said.
"In this case, it shows that our feelings and knowledge of our children affect how we actually perceive them. But it's important to consider that this mis-perception may actually make it easier to quickly distinguish one's youngest child from the other children," Kaufman said.
The study was published in the journal Current Biology.
