an overall trendp = 0.063
We observed an overall trend for preferring the Hollow stimulus (Mann-Whitney test: V = 27016.5, df = 1, p = 0.063), that turned out highly significant when considering only the chicks never exposed to filled stimuli, namely chicks imprinted on the Occluded and Hollow objects (Mann-Whitney test: V = 10721.5, df = 1, p = 0.009), see Fig 4B .