Dynamics of sensorimotor adaptation

Sen Cheng, Philip N SabesUniversity of California, San Francisco

Annual Swartz-Sloan Centers Meeting, 26th July 2005

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A simple sensorimotor task

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Motivation and outline

trial-by-trial dynamics

What is the learning rule of adaptation?1. What signals drive

learning?

2. Noise in the learning process?

3. Spatial anisotropies?

More powerful correlation between behavior and neural activity.

Steady-state of adaptation Compare average behavior

pre- and post-exposure

block design

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Virtual reality setup

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Concurrent test and exposure

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Model for dynamics of adaptation

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Linear dynamical system (LDS) ut : inputs (?)

xt : internal state, planned/expected reach error

yt : actual reach error

qt : learning noise

rt : motor noise

general state space model

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1. What signals drive learning?

2. Noise in the learning process?

3. Spatial anisotropies?

Questions

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Two candidate learning signals

System identification with expectation-maximization (EM) algorithm, Cheng and Sabes, 2005, submitted

Learning equation with two input signals

t : visual error

t : perturbation/ discrepancy betw. vision and proprioception

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Sample data and vis-model fit

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perturbation

reach error

model prediction

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Portmanteau test for serial autocorrelations

tt yy ˆIs the sequence of residuals a white noise sequence?

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Portmanteau statistic (Hosking, 1980)

Residual autocorrelations Portmanteau test for vis-model

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pert-model fit to sample data

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perturbation

reach error

vis-model

pert-model

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Portmanteau test cannot distinguish models

for vis-modelfor pert-model

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Likelihood ratio test (LRT) for nested models

M1: no input

M2: pert

M4: pert and vis

M3: vis error

p < 10-4 (n=18)p < 10-4 (n=18)

p=0.006 (n=1), p>0.067 (n=17) p>0.22 (n=18)

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ML

ML

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1. What signals drive learning?

2. Noise in the learning process?

3. Spatial anisotropies?

Questions

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The signal that drives learning

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apply to no feedback (noFB) reaches:

Estimated modelspert-model

vis-model

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pert-model

vis-model

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1. What signals drive learning? 2. Noise in the learning process?

3. Spatial anisotropies?

Questions

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Learning noise

stochastic

pert

LRT (n=18)

p < 10-4

noFB

LRT (n=18)p < 0.0003

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1. What signals drive learning? 2. Noise in the learning process? 3. Spatial anisotropies?

Questions

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Anisotropy in learning and noise

*

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Conclusions

LDS are good models for adaptation dynamics

New insights into adaptation1. Visual error drives adaptation predominantly

2. There is learning noise

3. Dynamics are anisotropic

Can now correlate trial-by-trial changes of behavior with neural activity.

supported by the Swartz foundation