Modeling the development of mirror neuronsGiorgio Metta, Paul Fitzpatrick • MIT AI Lab, Humanoid Robotics Group • {pasa,paulfitz}@ai.mit.edu
Acknowledgments: This work is funded by DARPA as part of the “Natural Tasking of Robots Based on Human Interaction Cues” project under contract number DABT 63-00-C-10102.
4MimicryThe robot mimics the observed action trying to fulfill the goal rather than an actual movement
Question: How do mirror neurons develop?Answer: Two stage hypothesis: learn about objects and then imitate the goal of an action if directed towards the same object.
Problem
FactsF5 contains two classes of neurons: canonical
and mirror. Both classes respond when object-directed actions are executed.
Canonical neurons respond to the presentation of an object according to the potential grasp types the object affords.
Mirror neurons respond to an observed action in accordance to the grasp type.
1
3
side tap
back slap
pull in
push away
A toy car: it rolls in the direction of its principal axis
A bottle: it rolls orthogonal to the direction of its principal axis
A toy cube: it doesn’t roll, it doesn’t have a principal axis
A ball: it rolls, it doesn’t have a principal axis
Motor vocabulary
identifyand
localizeobject
search rotation
Previously-pokedprototypes
Learn the “geometry” of pokingE.g. poking from the left causes the object to move to the right
-200 -150 -100 -50 0 50 100 150 2000
0.05
0.1
0.15
0.2
0.25
0.3
0.35
direction of movement [degrees]
P(x
)
back slap
-200 -150 -100 -50 0 50 100 150 2000
0.05
0.1
0.15
0.2
0.25
direction of movement [degrees]
P(x
)
side tap
side tap
back slap
Exploiting affordances during pokingWhen a known object is presented to the robot, it chooses the appropriate action to
make the object roll
Clustering
Interpreting observationsA foreign manipulator (human) pokes an object
The direction of movement is compared with the object afforadance
2
Final position
Initial position
Example 1
Final positionInitial position
Example 2
Final positionInitial position
Object, goal connects robot and human action
Our solutionWe used poking and prodding as a precursor to full-blown
manipulation
1. Learn about object affordances (canonical neurons)2. Interpret observations on the basis of affordances (mirror)
3. Poke/push objects according to their affordances4. Mimicry
12
34
Solution
Learn about object affordancesThe affordance considered is the direction of movement with respect to the object’s
principal axis
0 10 20 30 40 50 60 70 80 900
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
difference between angle of motion and principal axis of object [degrees]
estim
ate
d p
roba
bilit
y of
occ
urre
nce
Rolls at right angles toprincipal axis
Bottle, “pointiness”=0.13
MotivationOur inspiration comes from neuroscience: in particular, mirror neurons. This is a class of neurons found in the monkey's frontal cortex (area F5). A particular mirror neuron is activated both when the monkey executes an action and when it observes the same action performed by somebody else. Mirror neurons can be related to gesture recognition, language, and learning by imitation.
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