Perceptual organization refers to the process by which several visual elements are grouped in a coherent scene by the relationship among them. It is plausible that the general principles of perceptual organization are common between species because of environmental regularities, which are relatively independent from the specific niche of each species. The most relevant case is the segmentation of a visual scene in biologically relevant units, the objects which are composed by elements that can be analysed separately (local processing), but also integrated in a unitary percept by extracting the overall configuration (global processing). There are two important examples which demonstrate the advantage of global over local processing configuration. The first one concerns the Ebbinghaus illusion in which an object surrounded by small inducers appears larger than another surrounded by large inducers. In this case, to perceive the illusion it is essential to process the global configuration. This illusion has been extensively studied in humans. In animals, up to the present moment, it has been studied only in adult subjects of one primate species (baboons, Parron e Fagot, 2007) and in pigeons (Nakamura et al. 2008). We devised a procedure to test the Ebbinghaus illusion in domestic chicks: this species, which has been already employed for testing sensitivity to other visual illusions (e.g. Regolin & Vallortigara, 1995; Zanforlin, 1981) offers the advantage of allowing to test very young animals (being a precocial species), of controlling for the role of previous visual experience and allowing comparisons with data obtained in human infants and children. We reinforced chicks for choosing either a small or a large orange circle (for half of the chicks food was associated with the large circle, and vice versa for the other half). Subjects were then tested with Ebbinghaus-stimuli: two identical orange circles were presented one surrounded by large and the other by small gray inducer circles. Results suggest that the Ebbinghaus-illusion may be perceived at least by part of the chicks. Another important example which demonstrates the advantage of global over local processing configuration concerns the impossible objects in which several local cues need to be integrated to detect global inconsistencies in structural information, allowing discrimination between possible and impossible objects. Here we show that, after exposure to objects in which junctions providing cues to global structure were occluded, day-old chicks selectively approach the two-dimensional image that depicted the possible rather than impossible version of a three-dimensional object, after restoration of the junctions. Even more impressively, completely naive newly hatched chicks showed spontaneous preferences towards approaching two-dimensional depictions of structurally possible rather than impossible objects. These results show that natural selection can produce organisms perfectly able to deal with the problem of global coherence in three-dimensional objects as recovered from two-dimensional images in the absence of any specific experience of real three-dimensional objects.

Global processing of visual configurations in domestic chicks.

CAVAZZANA, ANNACHIARA;RUGANI, ROSA;REGOLIN, LUCIA
2011

Abstract

Perceptual organization refers to the process by which several visual elements are grouped in a coherent scene by the relationship among them. It is plausible that the general principles of perceptual organization are common between species because of environmental regularities, which are relatively independent from the specific niche of each species. The most relevant case is the segmentation of a visual scene in biologically relevant units, the objects which are composed by elements that can be analysed separately (local processing), but also integrated in a unitary percept by extracting the overall configuration (global processing). There are two important examples which demonstrate the advantage of global over local processing configuration. The first one concerns the Ebbinghaus illusion in which an object surrounded by small inducers appears larger than another surrounded by large inducers. In this case, to perceive the illusion it is essential to process the global configuration. This illusion has been extensively studied in humans. In animals, up to the present moment, it has been studied only in adult subjects of one primate species (baboons, Parron e Fagot, 2007) and in pigeons (Nakamura et al. 2008). We devised a procedure to test the Ebbinghaus illusion in domestic chicks: this species, which has been already employed for testing sensitivity to other visual illusions (e.g. Regolin & Vallortigara, 1995; Zanforlin, 1981) offers the advantage of allowing to test very young animals (being a precocial species), of controlling for the role of previous visual experience and allowing comparisons with data obtained in human infants and children. We reinforced chicks for choosing either a small or a large orange circle (for half of the chicks food was associated with the large circle, and vice versa for the other half). Subjects were then tested with Ebbinghaus-stimuli: two identical orange circles were presented one surrounded by large and the other by small gray inducer circles. Results suggest that the Ebbinghaus-illusion may be perceived at least by part of the chicks. Another important example which demonstrates the advantage of global over local processing configuration concerns the impossible objects in which several local cues need to be integrated to detect global inconsistencies in structural information, allowing discrimination between possible and impossible objects. Here we show that, after exposure to objects in which junctions providing cues to global structure were occluded, day-old chicks selectively approach the two-dimensional image that depicted the possible rather than impossible version of a three-dimensional object, after restoration of the junctions. Even more impressively, completely naive newly hatched chicks showed spontaneous preferences towards approaching two-dimensional depictions of structurally possible rather than impossible objects. These results show that natural selection can produce organisms perfectly able to deal with the problem of global coherence in three-dimensional objects as recovered from two-dimensional images in the absence of any specific experience of real three-dimensional objects.
2011
Atti del convegno Current challenges and applications of comparative cognition.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/2686677
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