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Dale Purves, Catherine Q. Howe; The statistics of natural scene geometry predict the perception of angles and line orientation. Journal of Vision 2004;4(8):40. doi: https://doi.org/10.1167/4.8.40.
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Stimuli that entail the intersection of two or more straight lines elicit a variety of well known perceptual anomalies. Preeminent among these effects are the systematic overestimation of acute angles, the underestimation of obtuse angles, and the misperceptions of line orientation exemplified in the classical tilt, Zöllner and Hering illusions. There is no generally accepted explanation of any of these effects. Since the size, distance and orientation of physical objects are conflated in any projection of light onto the retina, the real-world sources of the elements comprising the retinal image cannot be derived from the stimulus as such. This inevitable fact of vision, along with much other evidence, raises the possibility that these anomalous perceptions of angles and line orientation in geometrical stimuli are the result of a strategy of visual processing based wholly on the statistical relationship between images and their sources in natural scenes. To test this hypothesis we examined the relationship between projected images and their real-world sources in a database of range images acquired by laser range scanning. The results of this analysis show that the probability distributions of the possible real-world sources of projected lines and angles in natural scenes accurately predict each of these perceptual peculiarities. We conclude that the perception of angles and oriented lines is determined by the statistical relationship between the relevant geometrical stimuli and their physical sources in typical viewing environments, and the instantiation of this information in the neural circuitry of the visual system.
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