Pac-Man Configurations : Perhaps the most famous example of an illusory contour is the Pac-Man configuration popularized by Gaetano Kanizsa. Though not explicitly part of the image, Kanizsa figures evoke the percept of a shape, defined by a sharp illusory contour. Typically, the shape seems brighter than the background though luminance is in reality homogeneous. Additionally, the illusory shape seem to be closer to the viewer than the inducers. Kanizsa figures involve modal completion of the illusory shape and amodal completion of the inducers. The Ehrenstein illusion is of a bright disc.
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Gaetano Kanizsa , Italian artist and psychologist. Founder of the Institute of Psychology, Trieste. Kanizsa Triangle A symmetrical figure consisting of 3 discs each missing a triangular section, and 3 pairs of lines. Media Licence: Media Source: Fibonacci at Wikipedia The Kanizsa triangle illusion makes us realise the way our visual systems work—which we do not notice in our everyday experience.
Looking at the figure, most people will have the visual experience of an apparent brightness contour defining an upright triangle which is occluding three black discs and a second, inverted triangle outlined in black.
Note that both the Kanizsa triangle and the Kanizsa square create an illusion of depth — the central figure appears to sit in a higher plane than the inducing pacmen or the occluded downward pointing triangle. Figure 1 Kanizsa makes a distinction between modal and amodal completion of contours. In modal completion one has a visual experience as of an object in virtue of experiencing edges that appear to be created by a luminance, colour or texture boundary.
On reflection, one can tell that there is no such boundary and there is not a difference in luminance, colour or texture where there appears to be one; but, nonetheless, that is what we experience. In the Kaniza triangle the triangle that one seems to see pointing upwards, in virtue of a difference in luminance between it and the background, is a classic example of modal completion.
The apparent discs in the Ehrenstein figure are also an example of modal completion, as they are experienced in virtue of experiencing an apparent lightness boundary where none is present. In contrast to this, the triangle that one seems to see pointing downwards in the Kanizsa traingle image, that appears to be partly behind the upwards pointing triangle that we previously mentioned, provides an example of amodal completion.
The experience that one has of the downward pointing triangle does not consist in experienced boundaries consisting of colour, lightness or texture corresponding the occluded portion of the triangle. Yet, nonetheless, it does seem as if a triangle is present. This is a case of amodal completion, and it contrasts with modal completion in that it occurs when part of an object is experienced as occluded and is reported as having a particular shape, yet the occluded portion of the object is not experienced as being defined by colour, lightness or texture boundaries.
The horizontal and vertical lines in the Ehrenstein figure are usually perceived as amodally completed — they appear to continue behind the disc - but they are not experienced in virtue of an experience of an apparent luminance or colour boundary.
A good discussion of these phenomena from a psychological perspective is given in Gerbino, W. Philosophical accounts of modal and amodal perception can be found in Nanay , Briscoe , and Macpherson The mechanisms underlying contour completion and filling-in are not entirely understood.
A similar retinal stimulation is more often caused by one continuous surface occluding another, and so this is how the Kanizsa stimulus is represented by our perceptual system Rock and Anson As far as physiology goes, Peterhans et al. These cells correspond to elongated receptive fields on the retina and can fire selectively for both length and orientation of stimulus.
Activity in spatially separated, end-stopped cells may trigger a gating mechanism, allowing for communication between neurons at previously inactive synapses. References Dennett, D. Consciousness Explained, Penguin. Dennett, D. Prick and D. Friedman, H. Zhou, Pessoa and P. Gerbino, W. Grossberg, S. Petry and G. Kanizsa, G. Gerbino, Beck Ed.
Lawrence Earlbaum: NJ. Myin, E. De Nul, Bayne, A. Cleeremans and P. Nanay, B. Pessoa, L. Thompson and A. Peterhans, E. Baumartner, Rock, I. Anson, Macpherson ed.
GAETANO KANIZSA PDF
Dajar Kanizsa Triangle Illusion. The mechanisms underlying contour completion and filling-in are not entirely understood. Afterimage on empty shape also known as color dove illusion This type of illusions is designed to exploit graphical similarities. A figure in which three illusory contours form a triangle is known as a Kanizsa triangle. He attended the classic lyceum, and got the laurea post-secondary academic degree at the University of Padova inwriting a thesis about eidetic memory.
Tohoku Psychologica Folia, 3, Beck, J. Hillsdale, N. Benussi, V.