Anticipation of tennis-shot direction from whole-body movement: the role of movement amplitude and dynamics.

While recent studies indicate that observers are able to use dynamic information to anticipate whole-body actions like tennis shots, it is less clear whether the action's amplitude may also allow for anticipation. We therefore examined the role of movement dynamics and amplitude for the anticipation of tennis-shot direction. In a previous study, movement dynamics and amplitude were separated from the kinematics of tennis players' forehand groundstrokes. In the present study, these were manipulated and tennis shots were simulated. Three conditions were created in which shot-direction differences were either preserved or removed: Dynamics-Present-Amplitude-Present (D(P)A(P)), Dynamics-Present-Amplitude-Absent (D(P)A(A)), and Dynamics-Absent-Amplitude-Present (D(A)A(P)). Nineteen low-skill and 15 intermediate-skill tennis players watched the simulated shots and predicted shot direction from movements prior to ball-racket contact only. Percent of correctly predicted shots per condition was measured. On average, both groups' performance was superior when the dynamics were present (the D(P)A(P) and D(P)A(A) conditions) compared to when it was absent (the D(A)A(P) condition). However, the intermediate-skill players performed above chance independent of amplitude differences in shots (i.e., both the D(P)A(P) and D(P)A(A) conditions), whereas the low-skill group only performed above chance when amplitude differences were absent (the D(P)A(A) condition). These results suggest that the movement's dynamics but not their amplitude provides information from which tennis-shot direction can be anticipated. Furthermore, the successful extraction of dynamical information may be hampered by amplitude differences in a skill-dependent manner.