Philosophers have also been interested in what illusions like the Ponzo Illusion can tell us about the nature of experience. For a general discussion of cognitive penetration, see Macpherson (2012). their inner workings and outputs cannot be influenced by conscious awareness. So, in the case of the Ponzo Illusion, a standard way of explaining why experience of the illusion persists even though one knows that one is experiencing an illusion is that the module, or modules, which constitute the visual system are вЂcognitively impenetrableвЂ™ to some degree-i.e. To explain: on the hypothesis that the mind is modular, a mental module is a kind of semi-independent department of the mind which deals with particular types of inputs, and gives particular types of outputs, and whose inner workings are not accessible to the conscious awareness of the person-all one can get access to are the relevant outputs. The Ponzo Illusion is interesting because it is relevant to debates about modularity, cognitive penetration, and the nature of experience. Tilt constancy is the mechanism that enables perception of the stable orientation of objects despite changes in retinal or bodily orientation on the part of the perceiver (for discussion of this in comparison to the other two explanations, see Prinzmetal et al. More recently, it has been proposed that the illusion is caused by a вЂtilt constancyвЂ™ mechanism. According to this explanation, the linear perspective mechanism is activated such that the higher yellow line is perceived as being further away than the lower, but, in addition, a misapplied size constancy mechanism in the visual system makes the higher yellow line appear longer (see Gregory 1963, 1968). Another prominent example is the вЂmisapplied constancy scalingвЂ™ explanation (an explanation also employed by some to account for other geometrical visual illusions such as the MГјller-Lyer or Vertical-Horizontal illusions). Foreshortening is a technique used in perspective to create the illusion of an object receding strongly into the distance, by for example, drawing it smaller and higher-up on the page. One prominent example is the вЂlinear perspectiveвЂ™ explanation, according to which foreshortening is responsible for the illusory effect (see Gillam 1973). There have been a number of attempts to explain how the Ponzo Illusion works.

You can search for other such illusions in the Illusions Index.

These are sometimes called вЂgeometrical-optical illusionsвЂ™. other background/foreground lines, or other intersecting shapes.

the length, straightness, or parallelism of lines-appears distorted by other aspects of the image-e.g. The Ponzo Illusion is one among a number of illusions where a central aspect of a simple line image-e.g. The Ponzo Illusion was first published in the book Intorno ad alcune illusioni nel campo delle sensazioni tattili, sull'illusione di Aristotele e fenomeni analoghi in 1910. The Ponzo Illusion was discovered by Mario Ponzo (1882 - 1960), an Italian psychologist.

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