Novelty preference in face perception by week-old lambs (Ovis aries)

An extensive literature has been accumulating, in recent years, on face-processing in sheep and on the relevance of faces for social interaction in this species. In spite of this, spontaneous preferences for face or non-face stimuli in lambs have not been reported. In this study we tested the spontaneous preference of 8-day-old lambs (N = 9) for three pairs of stimuli. In each pair, one stimulus was a face-like display, whereas the other presented the same inner features displaced in unnatural positions. One pair of stimuli was obtained from photographic images of ewes’ faces, the other two pairs were schematic face-like stimuli. Lambs could differentiate the two stimuli obtained by photos of conspecifics, looking longer at the non-face stimulus (p < 0.05). We interpret this as a novelty preference, proving that few day-old lambs have already encoded the structural properties that define a face and recognize violations of those general properties.