Recent studies in motor learning suggest that directing attention to body parts can be disadvantageous for learning with respect to outcome variables compared to adopting an external focus, especially attending to the effects of one`s movements (Wulf & Prinz, 2001). However, few studies have investigated the phenomenon on the movement level. Therefore, this study had two main objectives: The first one was to find out whether the type of instruction (internal/external) has a long-term effect on kinematics and juggling-relevant ball-flight characteristics. Thereby, the implementation of the content of the instructions could be controlled and studied comparatively. The second objective referred to the question whether attentional foci make an impact on motor behavior when they are mediated by an action- or a representation-guided instruction. It is still unclear whether instructions are effective to the same extent when given in an early phase of modeling as the attention phase compared to the practice phase. To reveal whether internal and external instructions can be equally implemented in task execution and whether different timings of instructions in an observational learning paradigm influence motor behavior, we conducted 3D motion analyses within a factorial design. All juggling beginners were visually and verbally instructed to practice the discrete exchange juggling task. Two days after the acquisition phase, a retention and transfer phase took place without an instructed attentional focus. Four experimental groups were specifically instructed in terms of the factor "focus time" and the factor "focus type". The internal instruction asked the participants to focus on arms and hands with respect to the fact that juggling mainly arises from the forearm, not the whole arm. The external instruction made the participants focus on the balls that should only fly upright, not forward and backward and that the balls reach approximately the same height. Two groups received the respective instruction before model observation, the other two groups right before practice. A control group with no specific instruction was added. Before all participants observed the demonstration of an expert juggler, markers were attached on wrists, elbows, and shoulders for motion analyses. Three digital cameras recorded the jugglers´ movements and the balls. Five video clips were fed into an offline motion analysis system. All jugglers improved performance during the course of the experiment. No group differences with respect to correct trials could be detected. The variables that checked the instructional content on the behavioral level (kinematics and ball flight) revealed that the implementation of the adequate ball flight characteristics can also be achieved without corresponding instructions. Therefore, the external instruction did not additionally yield a benefit. On the contrary, the implementation of the internal instruction could only be shown for the instructed internal groups, irrespective of the fact when they were instructed. Additionally, the experimental group instructed to focus internally before and during practice showed worst accuracy in ball flight demands. This pattern of result hints to the possibility that the control of internal and external aspects differ in terms of difficulty and that outcome-related learning disadvantages of an internal attentional focus could be attributed to a more difficult control problem. The factor "focus time" proved to be of minor significance in this paradigm. Obviously, type-of-focusing effects can also be mediated by a representation-related instruction prior to observation. Finally, it can be stated that the registration of kinematics is a fruitful approach to determine the underlying movement patterns that guide the outcome data due to attentional focusing. How movement patterns differ related to the type of attentional focus and thereby produce differential performance scores needs to be clarified in the future.
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