Slower Visuomotor Corrections with Unchanged Latency are Consistent with Optimal Adaptation to Increased Endogenous Noise in the Elderly

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

Are there right hemisphere contributions to visually-guided movement? Manipulating left hand reaction time advantages in dextrals.

Many studies have argued for distinct but complementary contributions from each hemisphere in the control of movements to visual targets. Investigators have attempted to extend observations from patients with unilateral left- and right-hemisphere damage, to those using neurologically-intact participants, by assuming that each hand has privileged access to the contralateral hemisphere. Previous attempts to illustrate right hemispheric contributions to the control of aiming have focussed on increasing the spatial demands of an aiming task, to attenuate the typical right hand advantages, to try to enhance a left hand reaction time advantage in right-handed participants. These early attempts have not been successful. The present study circumnavigates some of the theoretical and methodological difficulties of some of the earlier experiments, by using three different tasks linked directly to specialized functions of the right hemisphere: bisecting, the gap effect, and visuospatial localization. None of these tasks were effective in reducing the magnitude of left hand reaction time advantages in right handers. Results are discussed in terms of alternatives to right hemispheric functional explanations of the effect, the one-dimensional nature of our target arrays, power and precision given the size of the left hand RT effect, and the utility of examining the proportions of participants who show these effects, rather than exclusive reliance on measures of central tendency and their associated null hypothesis significance tests

Are there right hemisphere contributions to visually-guided movement? Manipulating left hand reaction time advantages in dextrals

This is the final version of the article. It first appeared from Frontiers Media via http://dx.doi.org/10.3389/fpsyg.2015.01203Many studies have argued for distinct but complementary contributions from each hemisphere in the control of movements to visual targets. Investigators have attempted to extend observations from patients with unilateral left- and right-hemisphere damage, to those using neurologically-intact participants, by assuming that each hand has privileged access to the contralateral hemisphere. Previous attempts to illustrate right hemispheric contributions to the control of aiming have focussed on increasing the spatial demands of an aiming task, to attenuate the typical right hand advantages, to try to enhance a left hand reaction time advantage in right-handed participants. These early attempts have not been successful. The present study circumnavigates some of the theoretical and methodological difficulties of some of the earlier experiments, by using three different tasks linked directly to specialized functions of the right hemisphere: bisecting, the gap effect, and visuospatial localization. None of these tasks were effective in reducing the magnitude of left hand reaction time advantages in right handers. Results are discussed in terms of alternatives to right hemispheric functional explanations of the effect, the one-dimensional nature of our target arrays, power and precision given the size of the left hand RT effect, and the utility of examining the proportions of participants who show these effects, rather than exclusive reliance on measures of central tendency and their associated null hypothesis significance tests.We are grateful to Lorna Jakobson, A. David Milner, Irene Logan, John Orphan, Phil Surette, and Jim Urqhuart for expert technical assistance. Leah T. Johnstone and two anonymous referees provided detailed comments on this manuscript. This research was supported by Medical Research Council of Canada Grant MA-7269 to MG and a Wellcome Trust Travel Grant to DC

Decision-Making under Bounded Rationality and Model Uncertainty: an Information-Theoretic Approach

Artificial intelligence research and high computational power have recently led to break- throughs in solving high-dimensional reinforcement learning and sequential decision-making problems. The foundations of these advances rely on the classical theory of choice under uncer- tainty, the so-called Subjective Expected Utility (SEU) theory. However, SEU theory assumes two important unrealistic scenarios. First, it disregards computational limitations when mak- ing decisions by assuming perfectly rational agents i.e. agents with unlimited computational resources. Importantly, humans and artificial agents are bounded rational, or equivalently, they suffer from precision and computational limitations. Second, SEU theory assumes that the internal models employed for computation can be fully trusted and that they do not suffer from model uncertainty. However, any model of the environment is inherently incorrect and thus it should not be fully trusted. Therefore, humans and artificial agents are indeed subject to model uncertainty. This thesis consists of an experimental and a theoretical part. On the experimental side, I aimed to explain human sensorimotor behavior with information-theoretic models of bounded rationality and model uncertainty. In particular, we designed three experiments where we expose human subjects to decision-making scenarios involving model uncertainty. We dis- cover that human decision-making behavior can be explained by information-theoretic models that manifest as risk-sensitive and ambiguity-sensitive models. On the theoretical part, we developed a novel planning algorithm for sequential decision-making that accounts for both, information-processing constraints and model uncertainty. Finally, we examined and extended bounded rational models of decision-making under precision and time limitations whose we drew analogies with non-equilibrium thermodynamics. This non-equilibrium thermodynam- ical point of view allowed to connect decision-making with concepts such as dissipation and time-reversibility, and to discover novel relations connecting equilibrium with non-equilibrium decision-making. In conclusion, information-theoretic models of decision-making might be the missing cor- nerstone towards unifying principles of decision-making able to explain complex behavior beyond classic expected-utility models