The effect of motor difficulty on the acquisition of a computer task: a comparison between young and older adults

International audienceThe present study investigated the extent to which the impact of motor difficulty on the acquisition of a computer task varies as a function of age. Fourteen young and 14 older participants performed 352 sequences of 10 serial pointing movements with a wireless pen on a digitiser tablet. A conditional probabilistic structure governed the succession of target keys to be pointed at on a virtual keyboard. Detecting and learning with practice how to use this probabilistic structure was expected to allow the participants to anticipate the location of the targets, and thus to improve pointing performance in terms of speed, accuracy, and trajectory rectitude. Motor difficulty was manipulated through the size of the targets to be pointed at. Results showed that for older participants, but not for younger ones, motor difficulty had a detrimental effect on their ability to learn the probabilistic structure. This finding suggests that decreasing the target size provides complex detrimental influence on the performance, affecting the efficiency of both the motor and cognitive processes involved in the task, especially for the elderly

Advanced Processing Methods for Image-Based Displacement Field Measurement

International audienceWe present recent developments in data processing for velocity field estimation and visualization originating from computer vision. We review the current paradigm of PIV data processing, based on window correlation, and the regularization or variational approach which is dominant in optical flow estimation. We propose a novel unifying framework via the optimization of a compound regularized criterion written in terms of a dense displacement (or velocity) field. The paper then focuses on algorithmic issues.A fast iterative window correlation method leading to a highly parallel lgorithm termed FOLKI is described. Thanks to a GPU (Graphical Processing Unit) implementation, FOLKI reaches video rate for typical PIV data. Then we present more sophisticated solvers able to deal with the regularization term of the criterion, notably multigrid methods.In our view, these two components form the foundation of a video rate velocity field visualization and interpretation toolbox which, together with recent advances in experimental apparatus and numerical simulation, opens the way to a major development in experimental fluid science

Chemical composition, weed killer and antifungal activities of Tunisian thyme (Thymus capitatus Hoff. et Link.) essential oils

The chemical composition, phytotoxic and antifungal activities of the essential oils isolated by hydrodistillation from the aerial parts of Tunisian thyme were evaluated. In order to find best results, different variables (i.e. provenance and phase of plant development) were considered. The chemical composition analysed by gas chromatography/mass spectrometry (GC/MS) revealed variability among provenances displaying interesting chemotypes and that carvacrol (63–84%), limonene (5–10%), δ-terpinene (0–7%), and β-myrcene (0–7%) were the main components. Antifungal ability of Thymus capitatus essential oils was tested by disc agar diffusion against five phytopathogenic fungi: Fusarium avenaceum, F. culmorum, Microdochium nivale var. nivale, Alternaria sp., and Bipolaris sorokiniana. High antifungal activity was observed for the essential oil isolated at the post-flowering development phase for the Bekalta provenance. There was no difference in the antifungal activities of oils isolated at the flowering phase from the other provenances. Thyme essential oils showed high level of weed-killer activity as well against Sinapis arvensis

Predictive distribution models of European hake in the south-central Mediterranean Sea

The effective management and conservation of fishery resources requires knowledge of their spatial distribution and notably of their critical life history stages. Predictive modelling of the European hake (Merluccius merluccius L., 1758) distribution was developed in the south-central Mediterranean Sea by means of historical fisheries-independent databases available in the region. The study area included the international waters of the south-central Mediterranean Sea and the territorial waters of Italy, Malta, Tunisia and Libya. Distribution maps of predicted population abundance index, and probabilistic occurrence of recruits and large adults were obtained by means of generalized additive models using depth and seafloor characteristics as predictors. Presence/absence data of the two life stages was obtained using threshold values applied to the mean weight of the survey catches. Modelling results largely matched previously reported knowledge on habitat preference of the species and its critical life phases. Hake recruits showed an occurrence peak at 200 m depth with preference for soft bottoms. Large adults preferred deeper and harder bottom substrates. Prediction maps allowed to improve our knowledge on the distributional patterns of one of the most important shared stocks in the south-central Mediterranean. This knowledge is essential for an appropriate development of regional-spatial-based management plans