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Slower visuomotor corrections with unchanged latency are consistent with optimal adaptation to increased endogenous noise in the elderly.

Sherback M, Valero-Cuevas FJ, D'Andrea R - PLoS Comput. Biol. (2010)

Bottom Line: The model reproduces the latency result from the cross-correlation method.When presented with increased noise, the computational model reproduces the experimentally observed age-related slowing and the observed lack of increased latency.The model provides a precise way to quantitatively formulate the long-standing hypothesis that age-related slowing is an adaptation to increased noise.

View Article: PubMed Central - PubMed

Affiliation: Institute for Dynamic Systems and Control, ETH-Zurich, Zurich, Switzerland. sherback@idsc.mavt.ethz.ch

ABSTRACT
We analyzed age-related changes in motor response in a visuomotor compensatory tracking task. Subjects used a manipulandum to attempt to keep a displayed cursor at the center of a screen despite random perturbations to its location. Cross-correlation analysis of the perturbation and the subject response showed no age-related increase in latency until the onset of response to the perturbation, but substantial slowing of the response itself. Results are consistent with age-related deterioration in the ratio of signal to noise in visuomotor response. The task is such that it is tractable to use Bayesian and quadratic optimality assumptions to construct a model for behavior. This model assumes that behavior resembles an optimal controller subject to noise, and parametrizes response in terms of latency, willingness to expend effort, noise intensity, and noise bandwidth. The model is consistent with the data for all young (n = 12, age 20-30) and most elderly (n = 12, age 65-92) subjects. The model reproduces the latency result from the cross-correlation method. When presented with increased noise, the computational model reproduces the experimentally observed age-related slowing and the observed lack of increased latency. The model provides a precise way to quantitatively formulate the long-standing hypothesis that age-related slowing is an adaptation to increased noise.

Show MeSH
Complexity: Hankel Singular Values.These histograms of normalized third and fourth Hankel Singular Values (HSVs) of inferred controllers suggest that the complexity of the behavior of the elderly is reduced (see the Discussion). The young are thin black lines, the elderly are wide gray bars. Fifth and higher HSVs are negligible.
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pcbi-1000708-g010: Complexity: Hankel Singular Values.These histograms of normalized third and fourth Hankel Singular Values (HSVs) of inferred controllers suggest that the complexity of the behavior of the elderly is reduced (see the Discussion). The young are thin black lines, the elderly are wide gray bars. Fifth and higher HSVs are negligible.

Mentions: We examined the normalized Hankel Singular Values (HSVs) of the optimal control models that we fit to the behavior of our subjects. We found that models fit to the elderly subjects have smaller third and fourth normalized HSVs as shown in histograms in Fig. 10. Taking the logarithms of the mean normalized third and fourth HSVs for each subject and again applying t-tests on young and elderly groups yields p-values of 0.018 and 0.026, indicating that simpler models are fitted by our method to the behavior of the elderly group. Higher HSVs were negligible.


Slower visuomotor corrections with unchanged latency are consistent with optimal adaptation to increased endogenous noise in the elderly.

Sherback M, Valero-Cuevas FJ, D'Andrea R - PLoS Comput. Biol. (2010)

Complexity: Hankel Singular Values.These histograms of normalized third and fourth Hankel Singular Values (HSVs) of inferred controllers suggest that the complexity of the behavior of the elderly is reduced (see the Discussion). The young are thin black lines, the elderly are wide gray bars. Fifth and higher HSVs are negligible.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2837393&req=5

pcbi-1000708-g010: Complexity: Hankel Singular Values.These histograms of normalized third and fourth Hankel Singular Values (HSVs) of inferred controllers suggest that the complexity of the behavior of the elderly is reduced (see the Discussion). The young are thin black lines, the elderly are wide gray bars. Fifth and higher HSVs are negligible.
Mentions: We examined the normalized Hankel Singular Values (HSVs) of the optimal control models that we fit to the behavior of our subjects. We found that models fit to the elderly subjects have smaller third and fourth normalized HSVs as shown in histograms in Fig. 10. Taking the logarithms of the mean normalized third and fourth HSVs for each subject and again applying t-tests on young and elderly groups yields p-values of 0.018 and 0.026, indicating that simpler models are fitted by our method to the behavior of the elderly group. Higher HSVs were negligible.

Bottom Line: The model reproduces the latency result from the cross-correlation method.When presented with increased noise, the computational model reproduces the experimentally observed age-related slowing and the observed lack of increased latency.The model provides a precise way to quantitatively formulate the long-standing hypothesis that age-related slowing is an adaptation to increased noise.

View Article: PubMed Central - PubMed

Affiliation: Institute for Dynamic Systems and Control, ETH-Zurich, Zurich, Switzerland. sherback@idsc.mavt.ethz.ch

ABSTRACT
We analyzed age-related changes in motor response in a visuomotor compensatory tracking task. Subjects used a manipulandum to attempt to keep a displayed cursor at the center of a screen despite random perturbations to its location. Cross-correlation analysis of the perturbation and the subject response showed no age-related increase in latency until the onset of response to the perturbation, but substantial slowing of the response itself. Results are consistent with age-related deterioration in the ratio of signal to noise in visuomotor response. The task is such that it is tractable to use Bayesian and quadratic optimality assumptions to construct a model for behavior. This model assumes that behavior resembles an optimal controller subject to noise, and parametrizes response in terms of latency, willingness to expend effort, noise intensity, and noise bandwidth. The model is consistent with the data for all young (n = 12, age 20-30) and most elderly (n = 12, age 65-92) subjects. The model reproduces the latency result from the cross-correlation method. When presented with increased noise, the computational model reproduces the experimentally observed age-related slowing and the observed lack of increased latency. The model provides a precise way to quantitatively formulate the long-standing hypothesis that age-related slowing is an adaptation to increased noise.

Show MeSH