Abstract
Behavioral and theoretical studies have focused on identifying the kinematic and temporal characteristics of various movements ranging from simple reaching to complex drawing and curved motions. These kinematic and temporal features have been quite instrumental in investigating the organizing principles that underlie trajectory formation. Similar kinematic constraints play also a critical role in the visual perception of abstract and biological motion stimuli, and in visual action recognition. To account for these observations in the visual perception and production of body motion we present a new model of trajectory formation inspired by geometrical invariance. The model proposes that movement duration, timing, and compositionality arise from cooperation among several geometries. Different geometries possess different measures of distance. Hence, depending on the selected geometry, movement duration is proportional to the corresponding distance parameter. Expressing these ideas mathematically, the model has led to concrete predictions concerning the kinematic and temporal features of both drawing and locomotion trajectories. The model has several important implications with respect to action observation and recognition and the underlying brain representations. Some of these implications were examined in a series of fMRI studies which point top the importance of geometrical invariances and kinematic laws in visual motion processing.