Carbon outclasses wood in racket paddles: Ratings of expert and intermediate tennis players.

Wooden racket paddles were modified with rubber and carbon fibre laminates and their differences tested in terms of flexural, damping, and coefficient of restitution properties. Four rackets types were designed: a wood reference, wood with rubber, carbon fibre 0°, and carbon fibre 90°. Seven expert and eight intermediate tennis players tested the rackets. To determine which of the four rackets suited the players best, we asked the players to compare the rackets two by two. After each pair tested, participants had to fill out a 4-item questionnaire in which different aspects of the rackets' performance were judged. The most preferred racket was the 0° carbon fibre racket, followed by the 90° carbon fibre racket, the wood racket and, finally, the 1-mm rubber racket. Thus, rackets with the highest stiffness, least damping, and highest coefficient of restitution were the most preferred. Interestingly, although experts and intermediate players overall judged the rackets in very similar ways according to force, vibration, and control, they were sensitive to quite different physical characteristics of the rackets.

Three sequential brain activations encode mental transformations of upright and inverted human bodies: a high resolution evoked potential study.

Human bodies provide a particularly rich source of visual information. Whereas most previous studies have focused on the neural mechanisms during the perception and recognition of human bodies, the aim of the present study was to investigate the time course and location of brain activation during mental imagery of human bodies. When participants were asked to imagine themselves in the position of a visually presented human body as seen from many different angles and at two orientations (upright or inverted), their reaction times were faster for upright as compared to inverted bodies and correlated differently with the tested angles. These behavioral effects were also reflected in brain activation patterns, but only during the time period from 220 to 490 ms after stimulus onset. Evoked potential mapping and electrical neuroimaging revealed three distinct and sequential steps of processing related to mental body transformation: (1) an early activation in temporo-occipital and temporo-parietal cortex (220-360 ms) that does not distinguish between upright and inverted bodies, but closely reflects the effort of mental transformation, followed (2) by an activation in temporo-occipital and medial parieto-occipital cortex (350-460 ms) that encodes mental transformation for upright bodies, and (3) a later activation in temporo-occipital and prefrontal cortex (390-490 ms) that encodes mental transformation for inverted bodies. These data suggest that the mental transformation of human bodies is not a single process but a sequence of temporally distinct processing steps, where each step reflects a distinct aspect of the transformation process that consists of activations in a network of posterior brain areas including extrastriate cortex, temporo-parietal cortex, and medial parieto-occipital cortex, as well as an anterior brain region in prefrontal cortex.