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Sensory-Motor Primitives as a Basis for Imitation: Linking
Perception to Action and Biology to Robotics
Presentation by Dan Hartmann
21 Feb 2006
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Imitation: “the capability to acquire new skills by observation, based on
the imitator’s existing behavioral repertoire”
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Motivation for Imitation
• Natural Systems– Development of language and communication– Learning and relearning skills for children,
athletes, and those recovering from injuries
• Artificial Systems– Automated programming and control of robots– More natural interaction with robots
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Learning Model
• Selective attention
• Mirror neurons:
• Motor primitives
• Classification-based learning system
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Mirror Neurons
• Shown to exist in humans and monkey
• The link between perception and action
• Research shows that infants can imitate facial expressions without visual feedback
• Suggests built in primitive movements, not learned
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Selective Attention
• Idea: Imitation is built on a perception system which is specially attuned to biological movements
• Specialized perception may use not only visual input, but motor primitives to predict and model
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Eye-tracking
• Studies involving participants watching unfamiliar movements, either with or without the goal of imitating them.
• Attention was the same, focused on the end-effector
• Only difference was pupil dilation
• Results serve as basis for attention model
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Motor Control and Motor Primitives
• A motor system is composed by a set of primitives
• These can be executed sequentially and super-positioned
• The span of the motor primitives is all possible motions of the motor system.
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Coding
• Primitives are combined into “motor programs”
• Mirror neurons map perception to motor programs
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Attentional Model
• Focus on the end-effector, resolution decreases with log of distance from focus
• More detail in Jenkins 2000
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Kinds of Primitives
• “discrete” - straight line movements
• “oscillatory” - repetitive movements
• “postural” – arrangement of joints
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New Skill Learning
• A simple match between a perceived and know skill reinforces that skill
• A “novel” match which shows performance error requires rehearsal and training
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Learning Expectations
• Learning more skills increases the chances of matching future skills, making learning easier
• Learning a skill similar to a known skill is faster than a totally new skill
• Refining a skill similar to another skill is more difficult because it may be improperly matched to the other skill