The identification of human actions and body postures viewed from different viewpoints was examined in four long-term priming experiments with static pictures of a human model. In Experiments 1 and 2 participants had to name or describe the pictures, and in Experiments 3 and 4 participants had to decide whether the pictures showed a possible or impossible body pose. Reliable priming effects were obtained only when priming and primed action or pose shared the same in-depth orientation (Experiments 1 and 4) and left-right reflection (Experiments 2 and 3). Having seen the same action or pose in a different orientation did not reliably facilitate identification performance later on. Also, there was no priming for poses that are impossible to perform with a human body, not even when an identical same-view prime was used. These findings suggest that the stored representations that mediate the identification of human actions and postures are viewpoint specific.One kind of stimulus that virtually all human observers encounter numerous times in their lives is other human beings, engaged in many different actions, resulting in an even greater variety of body postures. Identifying these actions and body postures must therefore be a major task of the human visual system. This task is not straightforward, though. Depending on the orientation and position of the acting body relative to the observer, different instances of a Requests for reprints should be addressed to A. Daems,

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The proficiency of human observers to identify body postures is examined in three experiments. We use a posture decision task in which participants are primed with either anatomically possible or impossible postures (in the latter case the upper and lower body face in opposite directions). In a long-term priming paradigm (i.e., in an initial priming block of trials and a subsequent test phase several minutes later), we manipulate the relation between priming and test postures with respect to the identity of the person in the body postures (Experiment 1), the prototypicality of the depth orientations (Experiment 2), and the variability of the priming orientations (Experiment 3). Reaction time to the test postures is the main dependent variable. In Experiment 1 it is found that priming of postures does not depend on the exact visual appearance of the actor (either same priming and test female or male figure or different figures), supporting the hypothesis that posture priming primarily is determined by the spatial relations between the body parts and much less by characteristics of the person involved. Long-term priming in our paradigm apparently is based on the reactivation of high-level posture representations that make abstraction of the identity of the human figure. In Experiment 2 we observe that privileged or prototypical orientations (e.g., 3/4 views) do not affect long-term priming of body postures. In Experiment 3, we find that increasing or decreasing the variability between the priming and test figures influences reaction time performance. Collectively, these results provide a better understanding of the flexibility (e.g., invariant to identity) and limits (e.g., depending on depth orientation) of the processes supporting human posture recognition.