Sharing food and kissing are among the signals babies use to interpret their social world
From:
Massachusetts Institute of Technology
January 20, 2022 -- Learning to navigate
social relationships is a skill that is critical for surviving in human
societies. For babies and young children, that means learning who they can
count on to take care of them.
MIT neuroscientists have now identified
a specific signal that young children and even babies use to determine whether
two people have a strong relationship and a mutual obligation to help each
other: whether those two people kiss, share food, or have other interactions
that involve sharing saliva.
In a new study, the researchers showed
that babies expect people who share saliva to come to one another's aid when
one person is in distress, much more so than when people share toys or interact
in other ways that do not involve saliva exchange. The findings suggest that
babies can use these cues to try to figure out who around them is most likely
to offer help, the researchers say.
"Babies don't know in advance which
relationships are the close and morally obligating ones, so they have to have
some way of learning this by looking at what happens around them," says
Rebecca Saxe, the John W. Jarve Professor of Brain and Cognitive Sciences, a
member of MIT's McGovern Institute for Brain Research, and the senior author of
the new study.
MIT postdoc Ashley Thomas is the lead
author of the study, which appears today in Science. Brandon Woo, a Harvard
University graduate student; Daniel Nettle, a professor of behavioral science
at Newcastle University; and Elizabeth Spelke, a professor of psychology at
Harvard, are also authors of the paper.
Sharing
saliva
In human societies, people typically
distinguish between "thick" and "thin" relationships. Thick
relationships, usually found between family members, feature strong levels of
attachment, obligation, and mutual responsiveness. Anthropologists have also
observed that people in thick relationships are more willing to share bodily
fluids such as saliva.
"That inspired both the question of
whether infants distinguish between those types of relationships, and whether
saliva sharing might be a really good cue they could use to recognize
them," Thomas says.
To study those questions, the
researchers observed toddlers (16.5 to 18.5 months) and babies (8.5 to 10
months) as they watched interactions between human actors and puppets. In the
first set of experiments, a puppet shared an orange with one actor, then tossed
a ball back and forth with a different actor.
After the children watched these initial
interactions, the researchers observed the children's reactions when the puppet
showed distress while sitting between the two actors. Based on an earlier study
of nonhuman primates, the researchers hypothesized that babies would look first
at the person whom they expected to help. That study showed that when baby
monkeys cry, other members of the troop look to the baby's parents, as if
expecting them to step in.
The MIT team found that the children
were more likely to look toward the actor who had shared food with the puppet,
not the one who had shared a toy, when the puppet was in distress.
In a second set of experiments, designed
to focus more specifically on saliva, the actor either placed her finger in her
mouth and then into the mouth of the puppet, or placed her finger on her
forehead and then onto the forehead of the puppet. Later, when the actor
expressed distress while standing between the two puppets, children watching
the video were more likely to look toward the puppet with whom she had shared
saliva.
Social
cues
The findings suggest that saliva sharing
is likely an important cue that helps infants to learn about their own social
relationships and those of people around them, the researchers say.
"The general skill of learning
about social relationships is very useful," Thomas says. "One reason
why this distinction between thick and thin might be important for infants in
particular, especially human infants, who depend on adults for longer than many
other species, is that it might be a good way to figure out who else can
provide the support that they depend on to survive."
The researchers did their first set of
studies shortly before Covid-19 lockdowns began, with babies who came to the
lab with their families. Later experiments were done over Zoom. The results
that the researchers saw were similar before and after the pandemic, confirming
that pandemic-related hygiene concerns did not affect the outcome.
"We actually know the results would
have been similar if it hadn't been for the pandemic," Saxe says.
"You might wonder, did kids start to think very differently about sharing
saliva when suddenly everybody was talking about hygiene all the time? So, for
that question, it's very useful that we had an initial data set collected
before the pandemic."
Doing the second set of studies on Zoom
also allowed the researchers to recruit a much more diverse group of children
because the subjects were not limited to families who could come to the lab in
Cambridge during normal working hours.
In future work, the researchers hope to
perform similar studies with infants in cultures that have different types of
family structures. In adult subjects, they plan to use functional magnetic
resonance imaging (fMRI) to study what parts of the brain are involved in
making saliva-based assessments about social relationships.
The research was funded by the National
Institutes of Health; the Patrick J. McGovern Foundation; the Guggenheim
Foundation; a Social Sciences and Humanities Research Council Doctoral
Fellowship; MIT's Center for Brains, Minds, and Machines; and the Siegel
Foundation.
https://www.sciencedaily.com/releases/2022/01/220120140732.htm
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