Emre Türkmen¹ (), Görkem Baysal¹, Dicle Dövencioğlu¹; ¹Middle East Technical University (METU), Ankara, Turkey

Visual shape cues to animacy are discussed along global and midlevel classes such as symmetry, head/limbs, and curvilinearity/rectilinearity. Local shape distortions are also shown to create rich percepts of transparent layers (e.g., a rainy windshield) but have not yet been tested for animacy. Here, we manipulated the contours of 2D shapes globally and locally to investigate perceived animacy. In Experiment 1, 11 animate-inanimate (e.g., bird-airplane) pairs were morphed into each other in seven steps. Participants were shown each shape (150 milliseconds, 20 repetitions) and asked to respond as "animate" or "inanimate." Psychometric curves fitted to the percentage of "animate" responses generated discrimination thresholds at 19.6-60.6% morph levels. Although animate shapes were significantly more curvilinear, we did not observe a systematic relationship between curvilinearity and the thresholds. In Experiment 2, we distorted the local disarray of 20 images to create their eidolons (equivalent appearance classes). We changed the reach-grain parameters of ten inanimate stimuli (Experiment 1) and ten insect-like stimuli with varying curvature (5) and symmetry (2) levels in their limbs. Participants were asked to adjust the reach-grain parameters for three modes: to make the stimulus look "underwater," "behind glass," or "animate." Group means for the reach-grain values for underwater and behind-glass conditions were compatible with previous findings, and reach values for animacy yielded a bimodal distribution. A repeated measures ANOVA revealed a main effect of mode on both reach and grain values, and reach (but not grain) values systematically changed with the curvature: As curvature increased, participants adjusted lower settings to reach parameters. Overall, this study provides further evidence for the perception of rich transparent layers by local distortions in the image. We also show that parametric manipulations in image distortions explain perceived animacy, and both global (curvilinearity) and local (reach) shape cues are important in discriminating animate from inanimate.

Acknowledgements: Research Universities Support Program Cooperation Protocol (ADEP Grant no 104-2023-11273)