Over the past two decades, scientists have shown that
babies only a few months old have a solid grasp on basic rules of the
physical world. They understand that objects can’t wink in and out of
existence, and that objects can’t “teleport” from one spot to another.
Now, an international team of researchers co-led by MIT’s Josh Tenenbaum
has found that infants can use that knowledge to form surprisingly
sophisticated expectations of how novel situations will unfold.
Furthermore, the scientists developed a computational model of infant
cognition that accurately predicts infants’ surprise at events that
violate their conception of the physical world.
The model, which simulates a type of intelligence known as pure reasoning,
calculates the probability of a particular event, given what it knows
about how objects behave. The close correlation between the model’s
predictions and the infants’ actual responses to such events suggests that
infants reason in a similar way, says Tenenbaum, associate professor of
cognitive science and computation at MIT.
“Real intelligence is about finding yourself in situations that you’ve
never been in before but that have some abstract principles in common with
your experience, and using that abstract knowledge to reason productively
in the new situation,” he says.
The study, which appears in the May 27 issue of Science, is the first step
in a long-term effort to “reverse-engineer” infant cognition by studying
babies at ages 3-, 6- and 12-months (and other key stages through the
first two years of life) to map out what they know about the physical and
social world. That “3-6-12″ project is part of a larger Intelligence
Initiative at MIT, launched this year with the goal of understanding the
nature of intelligence and replicating it in machines.
Tenenbaum and Luca Bonatti of the Universitat Pompeu Fabra in Barcelona
are co-senior authors of the Science paper; the co-lead authors are Erno
Teglas of Central European University in Hungary and Edward Vul, a former
MIT student who worked with Tenenbaum and is now at the University of
California at San Diego.
Elizabeth Spelke, a professor of psychology at Harvard University, did
much of the pioneering work showing that babies understand abstract
principles about the physical world. Spelke also demonstrated that infants’
level of surprise can be measured by how long they look at something: The
more unexpected the event, the longer they watch.
Tenenbaum and Vul developed a computational model, known as an
“ideal-observer model,” to predict how long infants would look at animated
scenarios that were more or less consistent with their knowledge of
objects’ behavior. The model starts with abstract principles of how
objects can behave in general (the same principles that Spelke showed
infants have), then runs multiple simulations of how objects could behave
in a given situation.
In one example, 12-month-olds were shown four objects – three blue, one
red – bouncing around a container. After some time, the scene would be
covered, and during that time, one of the objects would exit the container
through an opening.
If the scene was blocked very briefly (0.04 seconds), infants would be
surprised if one of the objects farthest from the exit had left the
container. If the scene was obscured longer (2 seconds), the distance from
exit became less important and they were surprised only if the rare (red)
object exited first. At intermediate times, both distance to the exit and
number of objects mattered.
The computational model accurately predicted how long babies would look at
the same exit event under a dozen different scenarios, varying number of
objects, spatial position and time delay. This marks the first time that
infant cognition has been modeled with such quantitative precision, and
suggests that infants reason by mentally simulating possible scenarios and
figuring out which outcome is most likely, based on a few physical
principles.
“We don’t yet have a unified theory of how cognition works, but we’re
starting to make progress on describing core aspects of cognition that
previously were only described intuitively. Now we’re describing them
mathematically,” Tenenbaum says.
In addition to performing similar studies with younger infants, Tenenbaum
plans to further refine his model by adding other physical principles that
babies appear to understand, such as gravity or friction. “We think
infants are much smarter, in a sense, than this model is,” he says. “We
now need to do more experiments and model a broader range of the existing
literature to test exactly what they know.”
He is also developing similar models for infants’ “intuitive psychology,”
or understanding of how other people act. Such models of normal infant
cognition could help researchers figure out what goes wrong in disorders
such as autism. “We have to understand more precisely what the normal case
is like in order to understand how it breaks,” Tenenbaum says.
The research was funded by the Ministerio de Ciencia E Innovaci??n (Spain),
the James S. McDonnell Foundation, the Office of Naval Research, the Army
Research Office, and the Marie Curie Disorders and Coherence of the
Embodied Self Research Training Network.
Anne Trafton
MIT News Office Continue reading →
