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  Learning of natural and synthetic biological motion

Jastorff, J., Kourtzi, Z., & Giese, M. (2003). Learning of natural and synthetic biological motion. Poster presented at 29th Göttingen Neurobiology Conference, 5th Meeting of the German Neuroscience Society 2003, Göttingen, Germany.

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Jastorff, J, Author              
Kourtzi, Z1, 2, Author              
Giese, MA, Author              
1Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497794              
2Department Human Perception, Cognition and Action, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497797              


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 Abstract: Human body motion presented as point-light stimuli can be readily recognized. Psychophysical experiments show that these impoverished stimuli are sufficient for the discrimination between different actions and even for the extraction of the gender and other details of the moving actor. Additionally, a few studies indicate the capability of humans to learn to discriminate different styles of natural movements (e.g. gaits or sports movements). However, it remains unknown whether this learning is based on innate templates for biological movement patterns, or if humans can learn new representations of arbitrary complex movements. We address this question by investigating whether subjects can learn artificial biological movement stimuli. Methods: The stimuli used in this study were generated by linear combination of prototypical trajectories in space-time using spatio-temporal morphable models (Giese & Poggio, 1999). We created two different classes of stimuli: (A) Stimuli derived by linear combination of dissimilar natural movements (e.g. walking, kicking and dancing). (B) Stimuli generated by animation of an artificial skeleton model that is highly dissimilar from naturally occurring body structures. The joint angle trajectories of the skeleton were given by linear combinations of synthetic sinusoidal trajectories. Their amplitudes and frequencies were approximately matched with the joint trajectories of human actors during natural movements. For both classes, several stimuli were created which served as prototypes for the morphing procedure. Subjects had to discriminate within one class between pairs of these stimuli that were defined by linear combinations with slightly dissimilar weights of the prototypes. The trajectories were presented as normal point light walkers (PLW), and as point light walker with position jitter (PLWJ). The PLWJ were generated by adding random displacements of the dots along the skeleton of the walker in each frame (similar to Beintema & Lappe, 2002). Each subject took part in three test blocks that were intersected by two blocks of training. Feedback was provided only during training. Results: Subjects trained with stimuli derived from natural movements (class A) learned the discrimination between novel patterns very quickly, regardless of the stimulus type (PLW/PLWJ). If the training stimuli were rotated 90 deg in the image plane against the test stimuli, we observed transfer of the learned representation only for the normal PLW but not for the PLWJ stimuli. The completely artificial stimuli (class B) were only presented as PLWJ. Subjects were able to learn these stimuli equally fast as the natural stimuli (class A). In addition, we found the same view dependence as for the natural stimuli. Conclusions: (1) New templates for movement recognition can be learned very quickly. (2) Learning affects at least two different levels of representation (local and holistic). (3) The learned holistic representations seem to be view-dependent. (4) There seem to be no significant differences between the learning process for stimuli derived from artificial and natural movements.


 Dates: 2003-06
 Publication Status: Published in print
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Title: 29th Göttingen Neurobiology Conference, 5th Meeting of the German Neuroscience Society 2003
Place of Event: Göttingen, Germany
Start-/End Date: 2003-06-12 - 2003-06-15

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Title: The Neurosciences from Basic Research to Therapy: Proceedings of the 29th Göttingen Neurobiology Conference and the 5th Meeting of the German Neuroscience Society 2003
Source Genre: Proceedings
Elsner, N, Editor
Zimmermann, H, Editor
Publ. Info: Sturrgart, Germany : Thieme
Pages: - Volume / Issue: - Sequence Number: 556 Start / End Page: 626 - 627 Identifier: ISBN: 3-13-137351-2