ABSTRACT
A gymnast accelerates her legs towards the lower asymmetric bar and precisely times the beat to take advantage of reactive forces to facilitate her upward swing. A wheelchair basketballer modulates the forces on the wheels of his chair to arrive in front of the basket at the same time as the pass from his team-mate. These anecdotal descriptions of skilled actions in sport have one important thing in common: they exemplify the significant spatio-temporal demands on the top-class athlete in complex and dynamic environments. These demands, highlighted daily in the sports media, have been more precisely quantified in scientific analyses. In ball games such as baseball and tennis, projectile speeds of between 36 and 46 ms−1 have been recorded (Glencross and Cibich 1977; Bahill and LaRitz 1984). The time windows afforded performers in high-level sport are typically measured in thousandths of a second (ms). For example, Regan (1986) has demonstrated how cricket batsmen often have only 230 ms to cope with late fluctuations in the flight of a ball approaching at 150 kilometres per hour (kph). Yet, skilled performers are capable of the most extraordinary precision in matching the spatio-temporal constraints of their sports and activities. For instance, long jumpers can accurately hit a 20-cm take-off board at the end of a 40-m run-up at speeds of around 10 ms−1 (Hay 1988). Additionally, Bootsma and van Wieringen (1990) have illustrated the consistency of bat control in national-level table-tennis players by calculating the variability in timing the initiation of an attacking forehand drive. Astonishingly, they found that typical values for timing variability in the stroke were between 2.03 and 4.72 ms. The theme of this book is that, in order to satisfy these task constraints, the sport performer is heavily dependent on the visual system to provide much of the information for perceiving and acting.
