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Barbara Knappmeyer, Martin A Giese, Heinrich H Bülthoff; Spatio-temporal caricature effects for facial motion. Journal of Vision 2003;3(9):304. doi: 10.1167/3.9.304.
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Caricature effects (=recognition advantage for slightly caricatured stimuli) have been robustly established for static pictures of faces (e.g., Rhodes et al., 1987; Benson & Perrett, 1994). It has been shown recently that temporal or spatial exaggerations of complex body movements improve recognition of individuals from point light displays (Hill & Pollick, 2000; Pollick et al. 2001). Here, we investigate whether similar caricature effects can be established for facial movements. We generated spatio-temporal caricatures of facial movements by combining a new algorithm for the linear combination of complex movement sequences (spatio- temporal morphable models; Giese et al., 2002) with a technique for the animation of photo-realistic head models (Blanz & Vetter, 1999). In a first experiment we tested the quality of this linear combination technique. Naturalness ratings from 7 observers were obtained. They had to rate an average-shaped head model, which was animated with three classes of motion trajectories: 1) original motion capture data, 2) approximations of the trajectories by the linear combination model, and 3) morphs between facial movement sequences of two different individuals. We found that the approximations were perceived as natural as the originals. Unexpectedly, the morphs were perceived as even more natural (t(6)=4.6, p<.01) than the original trajectories and their approximations. This might reflect the fact that the morphs tend to average out extreme movements. In a second experiment 14 observers had to distinguish between characteristic facial movements of two individuals applied to a face with average shape. The movements were presented with three different caricature levels (100%, 125%, 150%). We found a significant caricature effect: 150% caricatures were recognized better than the non-caricatured patterns (t(13)=2.5, p<.05). This result suggests that spatio-temporal exaggeration improves the recognition of identity from facial movements.
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