We tested the hypothesis that our ability to detect fine kinematics variations is tuned to reveal more subtle differences when the motion pattern belongs to the observer compared to another individual. To this purpose, we analyzed the responses of 15 subjects in a same-different task on pairs of movements, which could belong to one or two different subjects. Self vs. Other comparisons were obtained by presenting both the observer’s and another participant’s kinematics. Subjects responded faster and more accurately when they (...) observed their own gestures compared to movements of another participant. In the latter case, slight kinematic differences were more likely to remain undetected. These findings are discussed within an ecological framework: in observing others, we are more concerned with detection of goals and intentions, i.e., outstanding variations in motion patterns. Conversely, in self-observation detection of more subtle differences is required to facilitate learning and optimization of motor acts. (shrink)