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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.

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Cross-correlations.The mean cross-correlations for young and elderly show that there is no aggregate increase in response latency. This analysis is free of assumptions and makes it clear that there is a change in the post-onset response, but no change in the response latency. We removed spurious effects by subtracting  from each trial. The effects of perturbations on response persist longer when post onset response is slow, as seen here in elderly data. These averages were obtained at each lag value by averaging across trials 3–10 for all subjects, and then averaging across subjects.
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pcbi-1000708-g004: Cross-correlations.The mean cross-correlations for young and elderly show that there is no aggregate increase in response latency. This analysis is free of assumptions and makes it clear that there is a change in the post-onset response, but no change in the response latency. We removed spurious effects by subtracting from each trial. The effects of perturbations on response persist longer when post onset response is slow, as seen here in elderly data. These averages were obtained at each lag value by averaging across trials 3–10 for all subjects, and then averaging across subjects.

Mentions: Application of our model-free cross-correlation method yields mean inferred response latencies of 267 and 263 ms for young and elderly subjects. The precision of the inferred quantities is evidenced by the median intrasubject standard deviations of 36 and 44 ms. A two-tailed t-test [41] was used to compare the 12 young to the 12 elderly using the mean from each subject to avoid repeated measures bias. The measurements' distribution was consistent with normality with or without using logarithms. The t-test indicates that the 4 ms difference between the two means is not statistically significant . The averaged cross-correlation data of young and elderly subjects is presented in Fig. 4.


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)

Cross-correlations.The mean cross-correlations for young and elderly show that there is no aggregate increase in response latency. This analysis is free of assumptions and makes it clear that there is a change in the post-onset response, but no change in the response latency. We removed spurious effects by subtracting  from each trial. The effects of perturbations on response persist longer when post onset response is slow, as seen here in elderly data. These averages were obtained at each lag value by averaging across trials 3–10 for all subjects, and then averaging across subjects.
© Copyright Policy
Related In: Results  -  Collection

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

pcbi-1000708-g004: Cross-correlations.The mean cross-correlations for young and elderly show that there is no aggregate increase in response latency. This analysis is free of assumptions and makes it clear that there is a change in the post-onset response, but no change in the response latency. We removed spurious effects by subtracting from each trial. The effects of perturbations on response persist longer when post onset response is slow, as seen here in elderly data. These averages were obtained at each lag value by averaging across trials 3–10 for all subjects, and then averaging across subjects.
Mentions: Application of our model-free cross-correlation method yields mean inferred response latencies of 267 and 263 ms for young and elderly subjects. The precision of the inferred quantities is evidenced by the median intrasubject standard deviations of 36 and 44 ms. A two-tailed t-test [41] was used to compare the 12 young to the 12 elderly using the mean from each subject to avoid repeated measures bias. The measurements' distribution was consistent with normality with or without using logarithms. The t-test indicates that the 4 ms difference between the two means is not statistically significant . The averaged cross-correlation data of young and elderly subjects is presented in Fig. 4.

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