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A comparison of force adaptation in toddlers and adults during a drawer opening task
(2025) Faßbender, Laura; Falck, Johannes; López, Francisco M.; Shing, Yee Lee; Triesch, Jochen; Schwarzer, Gudrun
Adapting movements to rapidly changing conditions is fundamental for interacting with our dynamic environment. This adaptability relies on internal models that predict and evaluate sensory outcomes to adjust motor commands. Even infants anticipate object properties for efficient grasping, suggesting the use of internal models. However, how internal models are adapted in early childhood remains largely unexplored. This study investigated a naturalistic force adaptation task in 1.5-, 3-year-olds, and young adults. Participants opened a drawer with temporarily increased resistance, creating sensory prediction errors between predicted and actual drawer dynamics. After perturbation, all age groups showed lower peak speed, longer movement time, and more movement units with trial-wise changes analyzed as adaptation process. Results revealed no age differences in adapting peak speed and movement units, but 1.5- and 3-year-olds exhibited higher trial-to-trial variability and were slower in adapting their movement time, although they also adapted their movement time more strongly. Upon removal of perturbation, we found significant aftereffects across all age groups, indicating effective internal model adaptation. These results suggest that even 1.5-year-olds form internal models of force parameters and adapt them to reduce sensory prediction errors, possibly through more exploration and with more variable movement dynamics compared to adults.
Determining the 2D spatial distribution of plasma parameters in a cylindrical cross section of a radio-frequency ion thruster by optical emission spectroscopy
(2025) Becker, Felix; Sarnoch, Pascal; Holste, Kristof; Leiter, Hans; Klar, Peter J.
Gridded ion engines, such as the radio-frequency ion thruster, are highly efficient designs for generating thrust on satellites or spacecrafts for both commercial and scientific missions, due to the very high exhaust velocities achieved. A thorough understanding of the low-temperature and low-pressure plasma parameters is essential in order to characterize, design, and optimize such a thruster. Corresponding plasma parameters can be obtained non-invasively from empirical correlations between the results of Langmuir double probe measurements and optical emission spectroscopy. The plasma parameters can be extracted solely from the recorded optical emission spectra once such an empirical correlation is established for a specific experimental setup and various operation conditions. Light from an object plane at a specified depth within the plasma is focussed onto the projection plane, using a telescopic arrangement of lenses and an aperture. Despite being out of focus, the grid structure is still identifiable though slightly blurred. By carefully scanning across this image, taking spectra at every light spot, we can record a series of optical emission spectra where each spectrum corresponds to a plasma volume located in the object plane behind a grid hole. The object plane is a 2D cross section within the bulk of the plasma at a distance of 5 cm behind the grid. Our approach therefore allows us to monitor the spatial profiles of plasma parameters in this cross section of the RIT 10 for different operating points of the thruster. Such spatial profiles are essential for characterizing thruster performance and improving global modeling of such thrusters. We believe that this method is also applicable for RITs of other sizes in the context of space qualification.
Accurately tracking visual moving stimuli with gaze requires a higher fidelity motion representation than perceptual discrimination
(2025) Wagner, Ilja; Murdison, T Scott; Gegenfurtner, Karl R; Goettker, Alexander
The human visual system evolved to process and interpret continuous visual input. However, visual signals in modern societies increasingly emanate from digital displays, which emulate continuous motion by presenting a series of discrete frames at some fixed temporal frequency. How does noncontinuous, sampled motion influence visual perception and action? We asked participants to complete a combined oculomotor and speed-discrimination task, where they tracked the motion of a stimulus via smooth pursuit eye movements and compared the velocity of the pursuit stimulus with a reference velocity. Motion quality was manipulated by presenting discrete frames at different temporal frequencies (120, 60, 30, and 15 Hz), covering a range of values corresponding to different motion qualia, from quasi-continuous (120 Hz) to highly discontinuous (15 Hz). We found that participants could reliably discriminate velocities, even at low refresh rates. However, measures of pursuit quality declined with decreasing refresh rate and increasing target velocity: a perception–action dissociation. The decline in pursuit accuracy can be explained by a model estimating a proxy for motion quality from the spatiotemporal energy profile of the stimuli. Using this estimate, our model predicts pursuit accuracy for arbitrary combinations of target velocity and refresh rate. Our results highlight the dissociation between perception and action in digital displays with sampled motion; while we may be able to accurately discriminate motion at reduced frame rates, acting on moving stimuli requires a higher fidelity motion representation
Experimental infection of shrews (Crocidura russula) with Borna disease virus 1 : insights into viral spread and shedding
(2025) Nobach, Daniel; Raeder, Leif; Müller, Jana; Herzog, Sibylle; Eickmann, Markus; Herden, Christiane
Numbers of human encephalitis cases caused by infection with Borna disease virus 1 (BoDV1) increase continuously in endemic areas. The reservoir host of BoDV1 is the bicolored white-toothed shrew, albeit few naturally infected individuals of other shrew species have been detected. To establish a reliable experimental reservoir model, 15 greater white-toothed shrews were infected with a shrew-derived BoDV1 isolate by different inoculation routes (intracerebral, intranasal, oral, subcutaneous, and intraperitoneal) and monitored up to 41 days. Except for the oral route, all other animals (12/15) were successfully infected, and the majority of them displayed temporarily reduced feed intake and loss of body weight but no inflammatory lesions. Infectious virus was isolated from 11/12 infected animals. Viral RNA was demonstrated by qRT-PCR in the central nervous system (CNS) and the majority of organs. Immunohistochemistry demonstrated BoDV1 antigen in neurons and astrocytes in the CNS and peripheral nerves. High viral loads in the CNS and the spinal cord points towards spread from periphery to the CNS to enhance viral replication and subsequent centrifugal spread to organs capable of secretion and excretions. In general, successful experimental BoDV1 infection of shrews proves their usefulness as animal model, enabling further studies on maintenance, transmission, pathogenesis, and risk assessment for human spillover infections.
Differential expression of host invasion-associated genes by Sarcocystis calchasi in intermediate versus definitive hosts
(2025) Maier-Sam, Kristina; Rupp, Oliver; Voss, Anne; Nemitz, Saskia; Wollenweber, Tassilo E.; Procida-Kowalski, Tara; Wilhelm, Jochen; Gruber, Achim D.; Lierz, Michael
Sarcocystis calchasi is a pathogenic apicomplexan parasite affecting avian species of several orders. To complete its heteroxenous life cycle, S. calchasi infects a wide range of avian intermediate hosts and accipitriform raptors serve as definitive hosts. The mechanism of invasion into host cells is largely understood in other apicomplexan parasites, particularly Toxoplasma gondii, which also belongs to the family of Sarcocystidae. However, Sarcocystis species exhibit several distinguishing features in their life cycles and in their secretory organelles. The composition of secretory pathogenesis determinants, including surface antigens and secretory organelle proteins, has been shown to differ between closely related species, as evidenced by Sarcocystis neurona. In this study, whole-genome sequencing was performed on S. calchasi, and transcriptomes were determined by RNA-seq of S. calchasi sporozoites and bradyzoites derived from intermediate and definitive hosts as well as from merozoites propagated in primary embryonal pigeon liver cells. The S. calchasi genome contains homologs of genes encoding proteins associated with the well-conserved host invasion machinery like AMA1 and rhoptry neck proteins, albeit with a markedly reduced number of genes encoding surface antigens, rhoptry and dense granule proteins in comparison to T. gondii. Our transcriptome analysis revealed different gene expression profiles between S. calchasi sporozoites, merozoites and bradyzoites. Factors associated with host cell attachment (surface antigens and micronemal proteins) were expressed predominantly either in sporozoites and merozoites or in bradyzoites. As sporozoites and merozoites invade various intermediate hosts and cell types whereas bradyzoites enter definitive host intestinal epithelium, their differential expression patterns indicate that S. calchasi utilizes different sets of secretory pathogenesis determinants for host cell attachment and invasion, depending on the type of host and cell.