Principal Component Analysis of gait in Parkinson's disease: relevance of gait velocity.

Principal Component Analysis (PCA) is a method to estimate the relation between data points. We used PCA to analyse movements of the upper and lower extremities during treadmill walking in healthy subjects and two groups of Parkinsonian patients. Healthy subjects (n=35) showed a typical pattern with high values of PC1 and low values in a descending order of PC2-PC4. Increase of speed resulted in a significant increase of PC1 and a significant decrease of the following PC's. In more severely affected patients (n=19, UPDRS>20), PC1 was significantly decreased and PC2-PC4 were significantly increased compared to healthy subjects. Speed could be increased only within a small range without corresponding changes of the PC's. In less severely affected patients (n=17), significant differences of the PC's were only found with fast pace. Separate analysis of arms and legs revealed that these changes are only due to altered movements of the arm. Analysis of the pattern of PC's in response to changes of gait velocities reveal alterations even in less severely affected Parkinsonian patients. The changes of the PC's with higher gait velocities in healthy subjects are suggestive of an increase of intersegmental coordination. This is impaired even in less severely affected Parkinsonian patients.

How 24-month-olds form and transfer knowledge about tools: the role of perceptual, functional, causal, and feedback information.

This study investigated cognitive processes underlying tool use and knowledge transfer in 24-month-olds (N=123). Following a demonstration, participants chose a tool to reach a reward in a training transfer paradigm. Differing from previous research, various aspects considered to be relevant for children's performance were integrated within the same study design, and performance was examined on a trial-by-trial basis. More specifically, we analyzed how the following aspects affected toddlers' learning and transfer performance: causal information, degree of conflict between perceptually salient and functionally relevant information, and feedback information. Children with access to causal information outperformed children without corresponding information during the training and transfer phases. Perceptual conflict had a negative impact on transfer performance. However, children were quickly able to correct their choices based on feedback. Results are discussed in the light of recent accounts on tool use understanding.