Do Gravity-Related Sensory Information Enable the Enhancement of Cortical Proprioceptive Inputs When Planning a Step in Microgravity?

International audienceWe recently found that the cortical response to proprioceptive stimulation was greater when participants were planning a step than when they stood still, and that this sensory facilitation was suppressed in microgravity. The aim of the present study was to test whether the absence of gravity-related sensory afferents during movement planning in microgravity prevented the proprioceptive cortical processing to be enhanced. We reestablished a reference frame in microgravity by providing and translating a horizontal support on which the participants were standing and verified whether this procedure restored the proprioceptive facilitation. The slight translation of the base of support (lateral direction), which occurred prior to step initiation, stimulated at least cutaneous and vestibular receptors. The sensitivity to proprioceptive stimulation was assessed by measuring the amplitude of the cortical somatosensory-evoked potential (SEP, over the Cz electrode) following the vibration of the leg muscle. The vibration lasted 1 s and the participants were asked to either initiate a step at the vibration offset or to remain still. We found that the early SEP (90–160 ms) was smaller when the platform was translated than when it remained stationary, revealing the existence of an interference phenomenon (i.e., when proprioceptive stimulation is preceded by the stimulation of different sensory modalities evoked by the platform translation). By contrast, the late SEP (550 ms post proprioceptive stimulation onset) was greater when the translation preceded the vibration compared to a condition without pre-stimulation (i.e., no translation). This suggests that restoring a body reference system which is impaired in microgravity allowed a greater proprioceptive cortical processing. Importantly, however, the late SEP was similarly increased when participants either produced a step or remained still. We propose that the absence of step-induced facilitation of proprioceptive cortical processing results from a decreased weight of proprioception in the absence of balance constraints in microgravity

Copying Errors of Potters from Three Cultures: Predictable Directions for a so-Called Random Phenomenon

International audience"The impact of copying error on change in artifact morphology is studied through a field experiment with three groups of potters, each with a distinct potting tradition (one from France and two from India). The nine French potters and the 12 Indian potters had to reproduce – in five specimens – four different model shapes with two different weights of clay (in total, each potter threw 40 pots). Results show that the variability generated while copying depends on both the difficulty of the task and the cultural learning niches of the potters. We conclude that, even though unintended, the copying error is culturally constrained and therefore its amplitude and directions predictable. This is attributed to the cultural selection of motor skills during apprenticeship.

How does practise of internal Chinese martial arts influence postural reaction control?

International audienceThe aim of this study was to determine the effects of Chinese martial arts practice on postural reaction control after perturbation. Participants standing in Romberg tandem posture were subjected to an unexpected lateral platform translation with the eyes open or closed at two translation amplitudes. The peak displacement of the centre of pressure and of the centre of mass, and the onset latency of muscular activity (tibialis anterior, gastrocnemius, lumbodorsal muscular group, and rectus abdominis), were evaluated for martial arts practitioners and for sport and non-sport participants. Compared with the sport and non-sport participants, the martial arts group showed lower maximal centre of pressure and centre of mass peak displacements in both the lateral and anterior-posterior directions, but no difference was found in the onset of muscular responses. We conclude that martial arts practice influences postural reaction control during a fixed-support strategy in a tandem task. The martial arts group used the ankle joint more frequently than the sport and non-sport participants, especially in the eyes-closed conditions. Our results suggest that the better balance recovery in the martial arts group is a consequence of better control of biomechanical properties of the lower limbs (e.g. through muscular response by co-contraction), not a change in the neuromuscular temporal pattern

Modulation of proprioceptive inflow when initiating a step influences postural adjustments

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Coordination of upper and lower body during balance recovery following a support translation

International audienceStrategies for recovery of posture were studied after lateral mechanical perturbations. 11 participants standing in tandem stance were unexpectedly submitted to lateral support translations with the eyes open or closed at two translation amplitudes. The trajectories of the center of mass of the upper and lower body and muscle activities allowed identification of three strategies, involving either the ankle or the hip only, or both. Hip use increased with vision and with amplitude of perturbation. Short-to-medium latency electromyographic activities were observed in leg and trunk muscles, and long-latency responses in the back leg muscles. Vision increased the activity of both leg and trunk muscles but did not influence the onset of the muscular responses. These data suggest a hierarchy in the selection of these different strategies: the hip is mobilized when the perturbation is more destabilizing but this strategy has a cost and needs specific sensory information supplied by vision

Cultural attraction in pottery practice: Group-specific shape transformations by potters from three communities.

Pottery is a quintessential indicator of human cultural dynamics. Cultural alignment of behavioral repertoires and artifacts has been considered to rest upon two distinct dynamics: selective transmission of information and culture-specific biased transformation. In a cross-cultural field experiment, we tested whether community-specific morphological features of ceramic vessels would arise when the same unfamiliar shapes were reproduced by professional potters from three different communities who threw vessels using wheels. We analyzed the details of the underlying morphogenesis development of vessels in wheel throwing. When expert potters from three different communities of practice were instructed to faithfully reproduce common unfamiliar model shapes that were not parts of the daily repertoires, the morphometric variation in the final shape was not random; rather, different potters produced vessels with more morphometric variation among than within communities, indicating the presence of community-specific deviations of morphological features of vessels. Furthermore, this was found both in the final shape and in the underlying process of morphogenesis; there was more variation in the morphogenetic path among than within communities. These results suggest that the morphological features of ceramic vessels produced by potters reliably and nonrandomly diverge among different communities. The present study provides empirical evidence that collective alignment of morphological features of ceramic vessels can arise from the community-specific habits of fashioning clay

A preliminary study of rotation velocity regulation in pottery wheel-throwing: Fieldwork with Indian potters using the low-inertia kick-wheel

International audienceThe present study examined rotation velocity regulation in pottery wheel-throwing. Long assumed to be a key parameter in the control of the centrifugal force, we interpret its role rather as a means to control the linear velocity at the point of hand-clay contact. To test this hypothesis, we set up a field experiment with Indian potters working with a low-inertia kickwheel. Six expert potters were asked to produce eight types of pots (four shapes × two masses), each type in five specimens (in total each potter threw 40 vessels). We measured the rotation velocity during the pre-forming and forming fashioning phases, as well as the maximal vessel radii at the end of both phases. Results demonstrated that potters reduced the rotation velocity from the pre-forming phase to the forming phase, but also for the large clay masses compared to the small clay masses, and-uniquely during the forming phase-for the shapes characterized by the largest diameter. Overall, the observed decreases in rotation velocity corresponded to increases in mean vessel diameter, suggesting that the potters were applying a limit on the linear velocity. Our results thus provide empirical evidence supporting the role of linear velocity as a key functional parameter in wheel-throwing. Directly relating to the potter-vessel interaction, it indicates both when and by how much the rotation velocity deceleration caused by the exertion of manual pressure forces should be compensated, as well as how to avoid the risk of velocity-induced collapse. While only preliminary, our results also suggest that large-sized ancient wheel-thrown vessels were most likely produced using low-velocity and high-inertia wheels. Future work, examining rotation velocity regulation over different types of wheels, is needed to allow definite conclusions to be drawn

Individuals among the pots: how do traditional ceramic shapes vary between potters?

International audienceAt the crossroad of archaeology and experimental psychology, we addressed the issue of inter-individual variability in traditional ceramic shapes. The goal was to explore whether such variability could imply potter signatures. We setup a field experiment with five expert Nepalese potters, asking them to produce three shapes (replicated five times). The 2D profiles of the experimental productions were analyzed with a shape analysis method borrowed from biology. In a complementary experiment focusing on shape discrimination, the participants were asked to visually identify their own productions and those of their colleagues. Results indicated that the potters produced slightly but significantly different shapes. We assume that during apprenticeship individuals developed their own motor skills, which reflect upon the finished products. Interpreting shape variability in terms of individuals could provide supplementary information on the social organization of the production, either for modern or ancient periods. As for shape discrimination, our preliminary results indicated that a few potters visually distinguished individual signatures. Those craftsmen could play a key role in the selection and evolution of the traditional ceramic shapes

Traditional craftspeople are not copycats: Potter idiosyncrasies in vessel morphogenesis.

Ceramics are quintessential indicators of human culture and its evolution across generations of social learners. Cultural transmission and evolution theory frequently emphasizes apprentices' need for accurate imitation (high-fidelity copying) of their mentors' actions. However, the ensuing prediction of standardized fashioning patterns within communities of practice has not been directly addressed in handicraft traditions such as pottery throwing. To fill this gap, we analysed variation in vessel morphogenesis amongst and within traditional potters from culturally different workshops producing for the same market. We demonstrate that, for each vessel type studied, individual potters reliably followed distinctive routes through morphological space towards a much-less-variable common final shape. Our results indicate that mastering the pottery handicraft does not result from accurately reproducing a particular model behaviour specific to the community's cultural tradition. We provide evidence that, at the level of the elementary clay-deforming gestures, individual learning rather than simple imitation is required for the acquisition of a complex motor skill such as throwing pottery