Some like it "local": A review of hierarchical processing in non-human animals.
When seeing a visual image, humans prioritize the perception of global features, which is followed by the assessment of the local ones. This global precedence has been investigated using hierarchical stimuli that consist of a large, global shape formed by the spatial arrangement of small local shapes. Comparing non-human animals to humans, research on global and local processing has revealed a heterogeneous pattern of results with some species exhibiting a local precedence and others a global one. Many factors have been proposed to influence the global and local processing: internal factors (e.g., age, sex) and external elements or perceptual field variables (e.g., stimulus size, visual angle, eccentricity, sparsity). In this review, studies showing that different non-human species process hierarchical stimuli in the same (global precedence) or reverse (local precedence) direction as humans are first collated. Different ecological, perceptual, and anatomical features that may influence global and local processing are subsequently proposed based on a detailed analysis of these studies. This information is likely to improve our understanding of the mechanisms behind the perceptual organization and visual processing, and could explain the observed differences in hierarchical processing between species.