Recognising the style of spatially exaggerated tennis serves

A technique for the construction of exaggerated human movements was develop ed and its effectiveness tested for the case of categorising tennis serves as flat, slice, or topspin. The technique involves treating movements as po ints in a high-dimensional space and uses average movements as the basis fo r constructing exaggerated movements. Exaggerated movements of a particular style are defined as those points in the space of movements which lie on a line originating at the style average and in the direction defined by the difference between the style average and the grand average. In order to vis ualise the movements, computer animation techniques were employed to transf orm the three-dimensional coordinates of the movement into the motion of a solid-body figure. These solid-body models were used in perceptual experime nts to assess the effectiveness of the exaggeration technique. After an ini tial training session on the exemplars from the original library, subjects viewed the synthetic tennis-serve motions and in two separate sessions eith er made three-alternative, categorisation judgments after viewing a single serve or rated dissimilarity after viewing a pair of serves. Results from b oth accuracy in the categorisation task and structure of a multidimensional scaling solution of the matrix of dissimilarities indicated that, as dista nce from the grand average increased, the service motion became more distin ct and more accurately identified.