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A solid object--a frame enclosing rods--can be seen as having an illusory 'line' joining the tips of the rods.
Perception, 1977, volume 6, pages
Illusory line linking solid rods
Colin Ware, John M Kennedy
Division of Life Sciences, Scarborough College, University of Toronto, West
Ontario M1C 1A4,
Received 1 February 1977
Abstract. A solid object—a frame enclosing rods—can be seen as having an illusory 'line' joining
the tips of the rods.
Illusory contours are apparent lines and divisions cutting across regions of the
perceived display which are actually physically homogeneous (Osgood 1951). Figure 1
is a photograph of a three-dimensional object, which allows the viewer to perceive an
illusory contour.
Whether viewed directly, or via a photograph, the three-dimensional object can be
seen as having a peculiar 'line' linking the tips of the rods. This 'line' is visible in
static inspection of the object, in monocular and binocular inspection, and in
inspection during head motion, motion of the object, and motion of the background.
Fixation can be on the background (near or far) or the eyes can track the object, and
the 'line' will still be seen; although, as is usual with illusory contours, some subjects
report that sections of the 'line' (between adjacent rods) disappear when they are
directly inspected, notably in the static conditions.
Previous experimenters have used two-dimensional displays to create illusory
contours and perceived depth. It has been noted that in these displays it could be
Figure 1. Photograph of a three-dimensional object, approximately 20 cm x 12 cm x 2 cm.
Inspection of the object results in an impression of an 'illusory contour' joining the ends of the
Viewed directly, rather than in a photograph, the compelling impression is of a 'line' linking
coplanar rods, though stratification in depth is readily possible given a picture of the object, as here.
602 C Ware, J M Kennedy
that the contour is a result of depth cues forcing the viewer to perceive nonexistent
stratification in depth (Kanizsa 1976; Gregory 1972). The depth-cue theory has also
been argued to hold for some binocular displays that result in illusory contours
(Coren 1972).
The object shown in figure 1 has been inspected by many subjects, some of whom
have viewed it on many occasions and for prolonged periods (with considerable
interest!). The 'line' has been noted by the viewers to be present without any
perceived stratification in depth; that is, all the rods are seen as in the same depth,
and as linked by the 'line'. Presumably when looking at two-dimensional graphic
displays, the viewer is free to exercise pictorial depth-perception skills and to create
figure-ground reversals, etc. A three-dimensional display provides binocular cues,
head motion, object motion, and background motion as information for depth. The
viewer of such a display is much more constrained and thus it can be shown that
depth stratification is not necessary for perception of subjective contour.
We have made other solid objects (and also shapes on transparent surfaces) which
induce subjective figures. We have used both opaque and semitransparent materials
in their construction. It is of interest to note that the subjective figure can be seen
as 'space filling' (i.e., voluminous or 'solid') not just as linear or planar. Whether
linear, planar, or 'space-filling', the subjective figures can be seen as unambiguously
located at the same distance as the inducing strips or rods, not as overlapping the
inducing materials or as part of the background.
Evidently, the stratification-in-depth hypothesis is unsatisfactory as a general
explanation of subjective contours. Hence, alternative explanations are required, for
example the recent ones which invoke brightness contrast effects tied to appropriate
stimulus groupings (Kanizsa 1976), notably groupings of line and rod endings (Frisby
and Clatworthy 1975; Kennedy and Lee 1976).
Of course, the object of figure 1 leaves open the possibility that there are particular
conditions where the stratification-in-depth hypothesis is the most satisfactory
explanation. Just such a condition may be the one in which the form information is
binocular disparity (rather than the monocular brightness differences that are the
substrate for contrast effects). The key point that our object makes is that illusory
contours can be produced without prior stratification being the causal agent.
Coren S, 1972 "Subjective contours and apparent depth"
Psychological Review
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Frisby J P, Clatworthy J L, 1975 "Illusory contours: curious cases of simultaneous brightness
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Gregory R L, 1972 "Cognitive contours"
Nature (London)
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Kanizsa G, 1976 "Subjective contours"
Scientific American
234 April 48-52
Kennedy J M, Lee H, 1976 "A figure-density hypothesis and illusory contour brightness"
5 387-392
Osgood C E, 1951 Method and Theory in Experimental Psychology (London: Oxford University
p © 1976
Pion publication printed in Great Britain
... Moving into the third dimension raises issues of ecological validity, because J. J. Gibson argued that the kinds of illusions that Kanizsa discovered were "pictorial" and would not be noticed in the third dimension with a mobile viewer. However, other researchers have noted the robustness of such illusions even in stimulus rich environments (Metzger, 1970(Metzger, /1986Ware & Kennedy, 1977). Recently, Steven Lehar (2008) illustrated a Kanizsa illusion in space (Fig. 4), with the stimulus that one can manipulate with one's hands. ...
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Short Abstract Many Gestalt illusions reveal a constructive aspect of perceptual processing where the experience contains more explicit spatial information than the visual stimulus on which it is based. The experience of Gestalt illusions often appears as volumetric spatial structures bounded by continuous colored surfaces embedded in a volumetric space. This suggests a field theory principle of visual representation and computation in the brain. A two-dimensional reverse grassfire algorithm, and a three-dimensional reverse shock scaffold algorithm are presented as examples of parallel spatial algorithms that address the inverse optics problem The phenomenon of phase conjugate mirrors is invoked as a possible mechanism. Long Abstract Many Gestalt illusions reveal a constructive, or generative aspect of perceptual processing where the experience contains more explicit spatial information than the visual stimulus on which it is based. The experience of Gestalt illusions often appears as volumetric spatial structures bounded by continuous colored surfaces embedded in a volumetric space. These, and many other phenomena, suggest a field theory principle of visual representation and computation in the brain. That is, an essential aspect of neurocomputation involves extended spatial fields of energy interacting in lawful ways across the tissue of the brain, as a spatial computation taking place in a spatial medium. The explicitly spatial parallel nature of field theory computation offers a solution to the otherwise intractable inverse optics problem; that is, to reverse the optical projection to the retina, and reconstruct the three-dimensional configuration of objects and surfaces in the world that is most likely to have been the cause of the two-dimensional stimulus. A two-dimensional reverse grassfire algorithm, and a three-dimensional reverse shock scaffold algorithm are presented as examples of parallel spatial algorithms that address the inverse optics problem by essentially constructing every possible spatial interpretation simultaneously in parallel, and then selecting from that infinite set, the subset of patterns that embody the greatest intrinsic symmetry. The principle of nonlinear wave phenomena and phase conjugate mirrors is invoked as a possible mechanism. Keywords diffusion field theory Gestalt inverse optics grassfire illusion phase conjugate reification shock scaffold
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... Moreover, we have long had scattered evidence, and architects have long believed (Coren & Girgus, 1978;Fletcher, 1905, cited in Fisher & Lucas, 1969Goodyear, 1899;Luckiesh, 1922;Pirenne, 1970), that illusions can occur with a freely moving observer in a normal spatial environment. For example, the Ponzo illusionis obtained in three-dimensional constructions (Brislin & Keating, 1976;Leibowitz, Brislin, Perlmutter, & Hennessy, 1969) and in binocularreal-world views (Leibowitz et al., 1969); the Miiller-Lyerillusion(Miiller-Lyer, 1889/1981) occurs in three-dimensional constructions (DeLucia & Hochberg, 1985, 1986Massaro & Anderson, 1970;Miiller-Lyer, 1889/1981Nijhawan, 1991;Zanforlin, 1967); the Hering illusionand subjective contoursoccur with wiresand rods (DiLollo& Marshall, 1969;Ware & Kennedy, 1977);the vertical-horizontal illusion occurs with natural viewing conditions and familiar objects (Chapanis & Mankin, 1967;Luckiesh, 1922). ...
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The Müller-Lyer and Ponzo illusions were obtained under free binocular viewing of three-dimensional objects, and the function relating magnitude of illusion to fin angle, characteristic of converging-line versions of the Müller-Lyer pattern, was closely paralleled by volumetric (three-cone), line-free objects (but not with an erect, planar “walk-through” construction and moving observers). Illusions cannot be dismissed as artifacts of static, impoverished viewing, therefore, but must be explained within any general theory of perception. Perspective explanations have difficulties with such three-dimensional manifestations, and seem completely inapplicable to our further finding that approximately the same amount of illusion occurred in objects and patterns with no oblique lines or edges. Confusion or averaging theories, not themselves tested here, remain unthreatened by these data.
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Two experiments showed the influence of perceptual set on the perception of subjective contours. In the first, the perceived shape of a subjective-contour figure (a minimal version of the Ehrenstein configuration) was varied by altering the observer’s viewing set. The second experiment showed that apparent depth emerged in subjective-contour figures when observers were set to perceive the illusory contours.
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Most current models of the perception of visual space follow one of two courses. Some begin with a superficial analysis of the visual information contained in the light reflected from surfaces in a visual scene to the eye and then work out highly sophisticated information processing models of how that information is used. Others begin with a detailed analysis of the stimulus information available at the eye, and then provide only a superficial processing description, if they provide one at all. The empiricists, beginning with Helmholtz and followed by many others (e.g., Rock, Epstein, Leibowitz, and perhaps Hochberg) generally pursue the first approach, while Gibson and some of his disciples represent virtually all of the work on the second. It is my thesis that progress on space perception is doomed until we create a thoroughly Gibholtzian approach, in which the stimulus analysis is based on the information available from realistic scenes viewed by two-eyed, moving observers, and the processing analysis is based on how the richness of this stimulus information is extracted or picked up to construct representations of visual space in our heads. The present paper is in two parts. The first describes the major categories of available information contained in light, how those sources of information are related to each other, and how the perceiver acquires or comes into contact with such sources of information. The second part is concerned with how that information is processed or used. Finally, because we are able to perceive the layout of space when looking at photographs and paintings of scenes, and at sequences of pictures that create motion, the same pair of analyses - one for stimulus information and one for processing - is presented for cases in which one looks at flat displays of scenes and sequences of motion pictures.
Although illusory contours were first described nearly a century ago, researchers have only recently begun to approach a consensus on the processes underlying their formation. Neurophysiological and psychophysical evidence indicate that neural mechanisms of the early visual cortex subserve illusory contour generation, although cognitive factors play important roles in determining the final percept. I summarize experiments concerning the determinants of illusory contour strength and form, concentrating on findings particularly relevant to modeling. After establishing arguments for the early generation of illusory contours, I provide an overview of formation theories, culminating with descriptions of neural models. The constraints that experimental data place on models are outlined, and neural models are evaluated with respect to these constraints. Throughout the review, I indicate where further experimental and modeling research are critical.
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Abibliography on subjective contours and a brief summary of trends in research-on-thin problem are presented. The bibliography covers the years 1900–1990 and contains 445 entries, each briefly annotated with a code that indicates the general content and theoretical orientation of the item.
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Perception depends on the context, and this is why different contexts are likely to induce different perceptions. Therefore, the role of the researcher is to identify which contexts may enable her/him to draw conclusions on mechanisms underlying perception. After all, the difference between the control and the experimental condition in scientific research can be seen as a change in a specific aspect of the context: all being equal, except the independent variable. The importance of the context in perception is perhaps secondary only to its vastness and complexity. Here, we choose two distinct topics as research issues: an "old" problem, the formation of illusory contour surfaces, and a "new" one, the origins of visual masked priming. Illusory contours have been widely researched: Purghé and Coren (1992) counted more than 400 publications from 1900 to 1990. However, just a few of them deal with heterogeneous contexts, i.e., illusory contour inducers depicted against non-homogeneous backgrounds. In the first part of this work we illustrated five experiments which attempt to fill this gap. Our results confirmed previous findings found employing homogeneous contexts, and extended them to heterogeneous contexts, introducing new issues. In the second part of this work, we report a series of visual masked priming experiments that focused on between-trials factors: namely, frequency of occurrence and presentation order effects. Previous research on priming has taken into account primarily the frequency of congruent and incongruent trials, and in particular the prime validity effect: when the proportion of valid trials is higher than invalid trials, an increase in priming is obtained. However, standard randomization of trials was usually employed for presentation, making frequent trials more likely to occur on the initial trials. Thus, the effects of initial and overall trial frequencies have become intermingled. The new context employed here (a biased presentation order) shed some light on these effects. Results are in agreement with the recently proposed retroactive view of masked priming, in contrast to the classic spreading activation theories (Masson & Bodner, 2003).
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Perceived figures tend to have surface colour and to be comparatively dense in texture and saturated. These figure characteristics are found in many of the illusory contour figures examined heretofore but new figures presented here do not conform to these characteristics. Consequently, rather than explain subjective brightness effects as offshoots of figural processes, it may be better to begin with concepts of local brightness effects induced by the display, which are made perceptually effective when grouped by the eye.
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The phenomenal appearance of contours in the absence of abrupt stimulus gradients was 1st discovered by F. Schumann. Recently such contours have been produced in Julesz patterns using binocular disparity. Analysis indicates that both monocular and binocular subjective contours result from the presence of depth cues in the stimulus array. (18 ref.)
It is suggested that simultaneous brightness contrast mediated by lateral inhibition plays an important role in generating many illusory contours. These contours might reflect a further way in which lateral inhibition serves to clarify and sharpen the neural encoding of retinal images.
IT is surprisingly easy to devise simple line figures which evoke marked illusory contours. Unlike the well known brightness contrast effects, these illusory contours can occur in regions far removed from regions of physical intensity difference; and they can be orientated at any angle to physically present contours. Fig. 1 is the figure described by Kanizsa1. An illusory triangle is observed whose apices are determined by the blank sectors of the three disks. The ``created'' object appears to have sharp contours which bound a large region of enhanced brightness.