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Abstract

Natural biological movements can be easily recognized from point light stimuli. Learning might play an important role in the representation of such patterns as suggested by recent experiments that demonstrate that subjects can learn to discriminate style differences between natural movements. Such experiments do not answer the question whether such discrimination exploits representations of natural movement patterns that are already present, or if subjects are able to learn quickly novel representations for arbitrary complex movement patterns. To test this question we created artificial biological motion stimuli by motion morphing through linear combination of prototypical trajectories from dissimilar natural movements in space-time. These stimuli have similar low-level motion properties as natural patterns, but do not correspond to movements that can be executed by natural organisms. 14 subjects were trained with seven such artificial patterns in two training blocks, and tested in a discrimination experiment within a pair comparison paradigm. We found a robust learning effect with significant improvement of the performance after 10 to 20 presentations of the training stimuli. Testing subjects with (2D) rotated stimuli we found only weak view dependence of the discrimination performance. This result is potentially based on subjects using primarily local cues for the discrimination. Current experiments investigate the influence of global vs. local strategies on the view-dependence.