CogSci 1: Introduction to Cognitive Science

Intelligent control of action inbiology and engineering

Emanuel Todorov

Cognitive Science DepartmentUniversity of California San Diego

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Why do we have a brain?

• the purpose of the brain is to produce adaptable and complex movements

• movement is the only way we have– of interacting with the world– of communicating (speech, gestures, writing)

• sensory, memory and cognitive processes have evolved to guide movement

TREES DO NOT NEED BRAINS,BECAUSE THEY DO NOT HAVE MUSCLES

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vs.

High-level

vs.

Low-level

Levels of control

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5

Internal models: ability to (learn to) predictExternal stimulus

Response

Time

Self-generated stimulus

Response

Time

Normal Perturbed Adapted Aftereffect

Force

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Adaptation to force fields(Shadmehr et al)

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Hand vs. joint trajectories: Experimental design(Mistry and Schaal)

reaching to 3D target

robot creates toque-fieldin joint space

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hand trajectories joint trajectories

Task-irrelevant “error” is not compensated

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Example of robotic manipulation

The difference between robotic and human movement

Example of human manipulation

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Variability: a signature of complex computations

MCP

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( ) ( ) ( )( )1 1i i i ix t ax t u t !+ = + +2,1x

2,1u

State:Control:

Dynamics:

Taking advantage of redundancy: Example

*

1 2x x X+ =Noise: 2,1!

Task:

*

1 2/ 2x x X= =Desired State:

Redundancy Elimination

( ) ( )2

* 2 2

1 2 1 2x x X u u r+ ! + +Cost:

Optimal Control

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0 50 1000

3

6

path length (%)

TIP 1

TIP 2

TIP 1

TIP 2

TIP 1TIP 2

spatial paths

movement variability

Example of structured movement variability