How One Shot Learning Unfolds in the Brain, Janelle Weaver
These scientists research how two parts of the brain help a person learn quickly.
Imagine you go out to a restaurant and order oysters for the first time, then for
the main course you order your usual plate of chicken. Later that evening, your
stomach becomes upset and you start to develop hives on your skin. Because you
have eaten chicken many times before without becoming ill, you conclude after
this one experience that the oysters caused your symptoms.
When humans and other animals encounter an outcome they have never
previously experienced, it may be necessary to rapidly learn the link between
cause and effect in order to survive. After experiencing two events that are paired
together for the first time, animals can quickly learn that one caused the other.
This phenomenon, called one-shot learning, is very different from incremental
learning, in which new knowledge is acquired gradually through trial and error.
While much evidence supports the notion of dissociable memory systems for
one-shot and incremental learning, little is known about how one-shot learning
unfolds at the neural level or how the brain is capable of switching between
different types of learning strategies.
In a study published in this issue of PLOS Biology, Sang Wan Lee, John O’Doherty,
and Shinsuke Shimojo of the California Institute of Technology combined
computational, behavioral, and brain-imaging techniques to shed light on these
questions. According to the authors, their model is the only framework to date
that is optimized to account for one-shot learning. Their evidence suggests that
the hippocampus is selectively switched on when one-shot learning is predicted
to occur, and the ventrolateral prefrontal cortex may act as a switch to turn on
and off one-shot learning as required .
Their novel computational framework suggests that individuals learn causal
relationships more quickly when they are less certain about whether one event
caused another. The authors reasoned that when the uncertainty about cause
and effect is high, more focus is required to learn the causal relationship, resulting
in the high learning rate associated with one-shot learning. To test their
computational hypothesis, the researchers analyzed behavioral data and
functional magnetic resonance imaging (fMRI) data acquired from individuals who
performed a simple causal inference task in which learning could occur from a
single experience. In each trial, participants were presented with a sequence of
pictures followed by a positive or negative number reflecting a monetary
outcome. At the end of each round of trials, participants were then asked to rate
the likelihood that individual pictures would cause particular outcomes; these
ratings were used to determine causal uncertainty. If a participant learned the
association between a picture and an outcome that were paired together only
one time, that trial was considered a one-shot learning event.
When the researchers tested whether their causal uncertainty model best
explains the behavioral data, they found that it outperformed all seven alternative
learning models typically used to account for incremental learning. Analysis of the
fMRI data revealed that higher causal uncertainty was associated with increased
activation of the ventrolateral prefrontal cortex, while the hippocampus was
activated during one-shot learning events but not incremental learning events.
Moreover, activity in the ventrolateral prefrontal cortex was coupled to
hippocampal activity for very high learning rates but not learning rates associated
with more incremental learning. This finding suggests that the ventrolateral
prefrontal cortex uses knowledge about causal uncertainty to control a switch
that turns on the hippocampus when one-shot learning is needed.
Taken together, the findings suggest that the brain may solve the problem of
one-shot learning by computing uncertainty about the causal relationship
between events and adjusting learning rates to accommodate rapid learning
about those events. Developing a detailed account of when rapid learning takes
place and which brain areas are engaged in this process might shed new light on
more efficient learning strategies, in addition to superstitions, delusional
reasoning, and erroneous attributions of an outcome to the wrong cause. The
study may ultimately have substantial implications for real-world situations such
as medical diagnoses, lawsuit cases, and psychiatric diseases, such as
Weaver, Janelle. "How One-Shot Learning Unfolds in the Brain." PLoS Biology 13.4 (2015). Public Library of Science. Web. 11 Nov. 2016.
In this research on the brain, when do the scientists believe people learn causal relationships the fastest?