Out With the Old, In With the New: Are Western Commodity Producers Ready for Buyouts?

Agricultural and Food Policy,

Walking dynamics are symmetric (enough)

Many biological phenomena such as locomotion, circadian cycles, and breathing are rhythmic in nature and can be modeled as rhythmic dynamical systems. Dynamical systems modeling often involves neglecting certain characteristics of a physical system as a modeling convenience. For example, human locomotion is frequently treated as symmetric about the sagittal plane. In this work, we test this assumption by examining human walking dynamics around the steady-state (limit-cycle). Here we adapt statistical cross validation in order to examine whether there are statistically significant asymmetries, and even if so, test the consequences of assuming bilateral symmetry anyway. Indeed, we identify significant asymmetries in the dynamics of human walking, but nevertheless show that ignoring these asymmetries results in a more consistent and predictive model. In general, neglecting evident characteristics of a system can be more than a modeling convenience---it can produce a better model.Comment: Draft submitted to Journal of the Royal Society Interfac

Is Agricultural Policy Decoupling against Human Nature? Experimental Evidence of Fairness Expectations’ Contributions to Payment Incidence

The objective of this research is to measure individuals’ fairness expectations and relate them to their market behavior in a private-negotiation institution. By doing this, we may inform model parameterization of field data and increase understanding of payment incidence causation. We hypothesize agents will change both their market and UG behavior when the tenant/proposer receives a subsidy following a successful negotiation. We also hypothesize that agents’ market behavior does relate to their fairness expectations in the UG. Two economic experiments were developed to test our hypotheses, a market and an ultimatum bargaining game experiment. We recruited 106 undergraduate students and conducted the experiments in an experimental laboratory using a computer based market mechanism. Our findings suggest fairness expectations need to be considered as a possible constraint on agents’ profit maximization behavior in land markets. The experimental evidence indicates market sellers or landlords demand higher land rental prices when tenants receive per-unit subsidies. Their ability to obtain a higher price appears to be more formidable in markets with limited matching opportunities. We conclude fairness expectations may constrain individuals’ profit-maximization behavior in the land market and, in turn, affect payment incidence in this market.Agricultural and Food Policy,

Decoupled Programs, Payment Incidence, and Factor Markets: Evidence from Market Experiments

We use laboratory market experiments to assess the impact of asymmetric knowledge of a per-unit subsidy and the effect of a decoupled annual income subsidy on factor market outcomes. Results indicate that when the subsidy is tied to the factor as a per-unit subsidy, regardless of full or asymmetric knowledge for market participants, subsidized factor buyers distribute nearly 22 percent of the subsidy to factor sellers. When the subsidy is fully decoupled from the factor, as is the case with the annual payment, payment incidence is mitigated and prices are not statistically different from the no-policy treatment.laboratory market experiments, agricultural subsidies, subsidy incidence, land market, ex ante policy analysis, Agricultural and Food Policy, Institutional and Behavioral Economics, Q18, D03, C92,

Ranchers Diverse in Their Drought Management Strategies

Farm Management, Livestock Production/Industries,

Increasing Motor Noise Impairs Reinforcement Learning in Healthy Individuals.

Motor variability from exploration is crucial for reinforcement learning as it allows the nervous system to find new task solutions. However, motor variability from noise can be detrimental to learning and may underlie slowed reinforcement learning performance observed in individuals with cerebellar damage. Here we examine whether artificially increasing noise in healthy individuals slows reinforcement learning in a manner similar to that seen in patients with cerebellar damage. Participants used binary reinforcement to learn to rotate their reach angle in a series of directions. By comparing task performance between conditions with different levels of added noise, we show that adding a high level of noise-matched to a group of patients with cerebellar damage-slows learning. In additional experiments, we show that the detrimental effect of noise may lie in reinforcing incorrect behavior, rather than not reinforcing correct behavior. By comparing performance between healthy participants with added noise and a group of patients with cerebellar damage, we found that added noise does not slow the learning of the control group to the same degree observed in the patient group. Using a mechanistic model, we show that added noise in the present study matched patients' motor noise and total learning. However, increased exploration in the control group relative to the group with cerebellar damage supports faster learning. Our results suggest that motor noise slows reinforcement learning by impairing the mapping of reward to the correct action and that this may underlie deficits induced by cerebellar damage

Human locomotor adaptive learning is proportional to depression of cerebellar excitability

Human locomotor adaptive learning is thought to involve the cerebellum, but the neurophysiological mechanisms underlying this process are not known. While animal research has pointed to depressive modulation of cerebellar outputs, a direct correlation between adaptive learning and cerebellar depression has never been demonstrated. Here, we used transcranial magnetic stimulation to assess excitability changes occurring in the cerebellum and primary motor cortex (M1) after individuals learned a new locomotor pattern on a split-belt treadmill. To control for potential changes associated to task performance complexity, the same group of subjects was also assessed after performing 2 other locomotor tasks that did not elicit learning. We found that only adaptive learning resulted in reduction of cerebellar inhibition. This effect was strongly correlated with the magnitude of learning (r = 0.78). In contrast, M1 excitability changes were not specific to learning but rather occurred in association with task complexity performance. Our results demonstrate that locomotor adaptive learning in humans is proportional to cerebellar excitability depression. This finding supports the theory that adaptive learning is mediated, at least in part, by long-term depression in Purkinje cells. This knowledge opens the opportunity to target cerebellar processes with noninvasive brain stimulation to enhance motor learning

Dynamic modulation of cerebellar excitability for abrupt, but not gradual, visuomotor adaptation

The cerebellum is critically important for error driven adaptive motor learning, as evidenced by the fact that cerebellar patients do not adapt well to sudden predictable perturbations. However, recent work has shown that cerebellar patients adapt much better if the perturbation is gradually introduced. Here we explore physiological mechanisms that underlie this distinction between abrupt and gradual motor adaptation in humans. We used Transcranial Magnetic Stimulation (TMS) to evaluate whether neural mechanisms within the cerebellum contribute to either process during a visuomotor reach adaptation. When a visuomotor rotation was introduced abruptly, cerebellar excitability changed early in learning, and approached baseline levels near the end of the adaptation block. However, we observed no modulation of cerebellar excitability when we presented the visuomotor rotation gradually during learning. Similarly, we did not observe cerebellar modulation during trial-by-trial adaptation to random visuomotor displacements or during reaches without perturbations. This suggests that the cerebellum is most active during the early-phases of adaptation when large perturbations are successfully compensated

Population analysis of Legionella pneumophila reveals a basis for resistance to complement-mediated killing

Legionella pneumophila is the most common cause of the severe respiratory infection known as Legionnaires' disease. However, the microorganism is typically a symbiont of free-living amoeba, and our understanding of the bacterial factors that determine human pathogenicity is limited. Here we carried out a population genomic study of 902 L. pneumophila isolates from human clinical and environmental samples to examine their genetic diversity, global distribution and the basis for human pathogenicity. We find that the capacity for human disease is representative of the breadth of species diversity although some clones are more commonly associated with clinical infections. We identified a single gene (lag-1) to be most strongly associated with clinical isolates. lag-1, which encodes an O-acetyltransferase for lipopolysaccharide modification, has been distributed horizontally across all major phylogenetic clades of L. pneumophila by frequent recent recombination events. The gene confers resistance to complement-mediated killing in human serum by inhibiting deposition of classical pathway molecules on the bacterial surface. Furthermore, acquisition of lag-1 inhibits complement-dependent phagocytosis by human neutrophils, and promoted survival in a mouse model of pulmonary legionellosis. Thus, our results reveal L. pneumophila genetic traits linked to disease and provide a molecular basis for resistance to complement-mediated killing. The bacterium Legionella pneumophila can cause severe respiratory infection, but is typically a symbiont of free-living amoeba. Here, the authors analyse the genomes of 902 clinical and environmental isolates, and identify a bacterial gene that is strongly associated with human infection and confers resistance to complement-mediated killing.Peer reviewe

Locomotor adaptability in persons with unilateral transtibial amputation

Background Locomotor adaptation enables walkers to modify strategies when faced with challenging walking conditions. While a variety of neurological injuries can impair locomotor adaptability, the effect of a lower extremity amputation on adaptability is poorly understood. Objective Determine if locomotor adaptability is impaired in persons with unilateral transtibial amputation (TTA). Methods The locomotor adaptability of 10 persons with a TTA and 8 persons without an amputation was tested while walking on a split-belt treadmill with the parallel belts running at the same (tied) or different (split) speeds. In the split condition, participants walked for 15 minutes with the respective belts moving at 0.5 m/s and 1.5 m/s. Temporal spatial symmetry measures were used to evaluate reactive accommodations to the perturbation, and the adaptive/de-adaptive response. Results Persons with TTA and the reference group of persons without amputation both demonstrated highly symmetric walking at baseline. During the split adaptation and tied post-adaptation walking both groups responded with the expected reactive accommodations. Likewise, adaptive and de-adaptive responses were observed. The magnitude and rate of change in the adaptive and de-adaptive responses were similar for persons with TTA and those without an amputation. Furthermore, adaptability was no different based on belt assignment for the prosthetic limb during split adaptation walking. Conclusions Reactive changes and locomotor adaptation in response to a challenging and novel walking condition were similar in persons with TTA to those without an amputation. Results suggest persons with TTA have the capacity to modify locomotor strategies to meet the demands of most walking conditions despite challenges imposed by an amputation and use of a prosthetic limb