Perceptual grouping in capuchins: when local wins over global
Human perceptual system processes the global features of objects to identify them, proceeding then to a more fine-grained analysis of local details. Capuchins have a visual system similar to that of humans, but they are faster at identifying the local elements of a visual scene and then its global configuration. This local superiority emerges also in other monkeys: possibly it evolved as a response to different ecological pressures experienced by the different species.
A fundamental aspect of visual perception, concerns the ability to process the global and the local aspects of the stimuli. In order to visually identify the objects and segregate them from the background, we must be able to group their component into a coherent perceptual whole. Many studies on visual grouping focused on the ability of the subjects to process hierarchical stimuli, i.e. small (local) shapes arranged to form a larger (global) shape. Human beings identify more quickly the global configuration than the local elements.
A problem that remains unresolved in visual cognition is why the well-established advantage shown by humans in the processing of global properties of visual patterns, is not mimicked by other primates species which nevertheless share a very similar visual system. In fact, our studies, similarly to other studies regarding non-human primates, demonstrate that capuchins discriminate the local components of the hierarchical stimuli more accurately than their global structure, in particular when the local elements are relatively distant from one another. According to some authors, these results could underline a greater difficulty in monkeys, than in humans, in grouping the local elements into a coherent whole rather than a local advantage per se. It is still unclear if such a cross-species difference, may reflect the existence of different evolutionary patterns on perceptual grouping capabilities in different species.
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