Bimanual Grasping Adheres to Weber's Law.
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ABSTRACT:
SUBMITTER: Hesse C
PROVIDER: S-EPMC8641124 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Visual complexity is ubiquitous in nature. Drivers of complexity include selection in coevolutionary arms races between antagonists. However, the causes and consequences of biological complexity and its perception are largely understudied, partly because complexity is difficult to quantify. Here, we address this by studying egg pattern complexity and its perception in hosts (tawny-flanked prinia Prinia subflava), which visually recognize and reject mimetic eggs of their virulent brood parasite (cuckoo finch Anomalospiza imberbis). Using field data and an optimization algorithm, we compute a complexity metric which predicts rejection of experimentally placed conspecific eggs in prinia nests. Real cuckoo finch eggs exhibit significantly lower pattern complexity than prinia eggs, suggesting that high complexity benefits hosts because it distinguishes host eggs from parasitic eggs. We show that prinias perceive complexity differences according to Weber's law of proportional processing (i.e. relative, rather than absolute, differences between stimuli are processed in discrimination, such that two eggs with simple patterns are more easily discriminable than two with complex patterns). This may influence coevolutionary trajectories of hosts and parasites. The new methods presented for quantifying complexity and its perception can help us to understand selection pressures driving the evolution of complexity and its consequences for species interactions.
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Project description:Weber's law quantifies the perception of difference between stimuli. For instance, it can explain why we are less likely to detect the removal of three nuts from a bowl if the bowl is full than if it is nearly empty. This is an example of the magnitude effect - the phenomenon that the subjective perception of a linear difference between a pair of stimuli progressively diminishes when the average magnitude of the stimuli increases. Although discrimination performances of both human and animal subjects in various sensory modalities exhibit the magnitude effect, results sometimes systematically deviate from the quantitative predictions based on Weber's law. An attempt to reformulate the law to better fit data from acoustic discrimination tasks has been dubbed the "near-miss to Weber's law". Here, we tested the gustatory discrimination performance of nectar-feeding bats (Glossophaga soricina), in order to investigate whether the original version of Weber's law accurately predicts choice behavior in a two-alternative forced choice task. As expected, bats either preferred the sweeter of the two options or showed no preference. In 4 out of 6 bats the near-miss to Weber's law provided a better fit and Weber's law underestimated the magnitude effect. In order to test the generality of this observation in nectar-feeders, we reviewed previously published data on bats, hummingbirds, honeybees, and bumblebees. In all groups of animals the near-miss to Weber's law provided better fits than Weber's law. Furthermore, whereas the magnitude effect was stronger than predicted by Weber's law in vertebrates, it was weaker than predicted in insects. Thus nectar-feeding vertebrates and insects seem to differ in how their choice behavior changes as sugar concentration is increased. We discuss the ecological and evolutionary implications of the observed patterns of sugar concentration discrimination.
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Project description:The classic understanding of prehension is that of coordinated reaching and grasping. An alternative view is that the grasping in prehension emerges from independently controlled individual digit movements (the double-pointing model). The current study tested this latter model in bimanual prehension: participants had to grasp an object between their two index fingers. Right after the start of the movement, the future end position of one of the digits was perturbed. The perturbations resulted in expected changes in the kinematics of the perturbed digit but also in adjusted kinematics in the unperturbed digit. The latter effects showed up when the end position of the right index finger was perturbed, but not when the end position of the left index finger was perturbed. Because the absence of a coupling between the digits is the core assumption of the double-pointing model, finding any perturbation effects challenges this account of prehension; the double-pointing model predicts that the unperturbed digit would be unaffected by the perturbation. The authors conclude that the movement of the digits in prehension is coupled into a grasping component.
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Project description:IntroductionParkinson's disease (PD) disrupts the control and coordination of grasping forces, likely due to a disruption in basal ganglia circuitry and diminished activity within the supplementary motor area (SMA). High intensity aerobic exercise has been shown to enhance connectivity between basal ganglia nuclei and cortical areas, including the SMA. The aim of this project was to determine the effects of high intensity lower extremity exercise on motor control patterns underlying a manual dexterity task.MethodsPD participants completed eight weeks of high intensity aerobic exercise under forced or voluntary exercise (FE or VE) modalities. Grasping forces for each limb were quantified during a functional bimanual dexterity task. Data were collected while OFF antiparkinsonian medication at baseline, end of treatment (EOT), and eight weeks after exercise cessation (EOT+8).ResultsEight weeks of high intensity exercise improved MDS-UPDRS Motor III clinical ratings by more than 4 points (~15%) for the FE and VE groups. Time to complete the task decreased nearly 30% across both groups as well. The control and coordination of grasping forces, simultaneity of force initiation, and rate of grip and load force exhibited significant improvements following exercise. In general, improvements in biomechanical outcomes were sustained following exercise cessation.ConclusionHigh intensity aerobic exercise, achieved via a forced or voluntary mode, improved PD symptoms and bimanual dexterity. Sustained improvement of upper extremity motor control following exercise cessation indicates high intensity exercise enhances CNS functioning and suggests exercise may be a candidate for altering PD progression.
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