Biological predispositions influence approach and avoid responses from the time of birth or hatching. Neonates of species that require parental care (e.g. human babies and chicks of the domestic fowl) are attracted by stimuli associated with animate social partners, such as face-like configurations, biological motion and self-propulsion. The property of being filled is used as a cue of animacy by 8-month-old human infants but it is not known whether this reflects the effect of previous experience. We used chicks of the domestic fowl (Gallus gallus) to investigate whether the property of being filled vs. hollow elicits spontaneous or learned preferences. To this aim we tested preferences of naïve and imprinted chicks for hollow and closed cylinders. Contrary to our expectations, we documented an unlearned attraction for hollow stimuli. The preference for hollow stimuli decreased when chicks were imprinted on filled stimuli but did not increase when chicks were imprinted on hollow stimuli, suggesting that hollowness is not crucial to determine affiliative responses for imprinting objects. When chicks were imprinted on occluded stimuli that could be either filled or hollow, the preference for hollow stimuli emerged again, showing that imprinting does not disrupt the spontaneous preference for hollow objects. Further experiments revealed that hollow objects were mainly attractive by means of depth cues such as darker innards, more than as places to hide or as objects with high contrast. Our findings point to predisposed preferences for hollow objects, and suggest that early predispositions might be driven by factors different from animacy cues.

10Biological predispositions influence approach and avoid responses since the beginning of 11 life. Neonates of species that require parental care (e.g. human babies and chicks of the 12 domestic fowl) are attracted by stimuli associated with animate social partners, such as 13 face---like configurations, biological motion and self---propulsion. The property of being 14 filled is used as a cue of animacy by 8---month---old infants but it is not known whether this 15 reflects the effect of previous experience. We use chicks of the domestic fowl (Gallus 16 gallus) to investigate whether the property of being filled vs. hollow elicits spontaneous 17 or learned preferences. To this aim we tested preferences of naıve and imprinted chicks 18 for hollow and closed cylinders. Contrary to our expectations, we documented an 19 unlearned attraction for hollow stimuli. The preference for hollow stimuli decreased 20 when chicks were imprinted on filled stimuli but did not increase when chicks were 21 imprinted on hollow stimuli, suggesting that this feature is not crucial to categorize the 22 familiarity of imprinting objects. When chicks were imprinted on occluded stimuli that 23 could be either filled or hollow, the preference for hollow stimuli emerged again, 24showing that imprinting does not disrupt the spontaneous preference for hollow objects. 25. CC-BY-NC-ND 4.0 International license not peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/050799 doi: bioRxiv preprint first posted online Apr. 28, 2016; 2 Further experiments revealed that hollow objects were mainly attractive by means of 26 depth cues such as darker innards, more than as places to hide or as objects with high 27 contrast. Our findings point to predisposed preferences for hollow objects that might be 28 unrelated to social behaviour. 29 30

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