INVITED TALKS"Illusions of motion perception"
Stuart Anstis(Dept of Psychology, University of California, San Diego, USA)
Abstract:
I have discovered various illusions that demonstrate how luminance,contrast, size and context influence perceived motion.
Reverse phi illusion: objects that reverse their polarity in successive
movie frames appear to move backwards.
Footsteps illusion: a light and a dark square move at constant speed
across stationary black and white stripes appear to move alternately
faster and slower. Reason: low-contrast motion looks slower.
Flying bugs illusion: the perceived orbits of circling bugs depend
upon their motion relative to the background, not upon absolute
motion.
Zigzag illusion: a field of random dots appears to move the rightwhen viewed from close up, but downwards when viewed from adistance.
Peripheral motion: Disks moving across static stripes backgrounds
look strongly distorted in the periphery.
Global versus local organization: Ambiguously moving spots
spontaneously re-group perceptually into large or small groups thatmove in different directions.
Chopsticks illusion: when orthogonal lines slide across each other,
the intersection of the lines actually moves clockwise but it appear tomove strongly counterclockwise.
Flash-grab illusion: the positions of flashed targets are strongly
distorted by nearby moving objects.

"Motion illusions as a tool to understand brain
mechanisms in typical developing individuals andin clinical populations."
Simone Gori(Developmental and Cognitive Neuroscience lab, Department ofGeneral Psychology, University of Padua; Developmental
Neuropsychology Unit, Scientific Institute "E. Medea," Italy)
Abstract:
Motion illusions act as a non-invasive window into the neurobiologyof our visual system. Motion illusion refers to a perception of motionthat is absent or different in the physical stimulus. Motion illusions
are non-veridical percepts that uncover the processes by which
veridical perception mediates our representation of motion. Thesephenomena are exceptions able to reveal the brain signature
superimposed on the stimulus: the constraints of the visual systemitself. I will present some motion illusions that are able to reveal
information about how the motion is processed and elaborated byour visual system. Moreover, I will show how motion illusions canshed light on the peculiar visual systems of clinical populations.

"Motion capture in terms of illusory motion signal
obtained from oblique lines"
Makoto Ichikawa(Department of Psychology, Chiba University, Japan)

Abstract:
When observers move the head backwards and forwards while
fixating on the center of the concentric circles that consist of obliquelines, they see illusory rotation of those circles. If several dots aresuperimposed on the concentric circles, observers see the illusory
rotation not only for the circles, but also for those dots. This illusory
rotation of the dots is based on motion capture. We examined how
the amount of dots affects the motion capture, and found that themotion capture was facilitated by the increment of the dots. In
addition, we found that, if observers see both expansion/contraction
and rotation of the circles, the direction of motion capture tended tobe the same with that of the inner circle while, if observers see onlyrotation of the circles, the direction of the motion capture was
frequently opposite to that of the inner circle. These results suggestthat the motion capture depends upon the local leakage of motion

signal from the circles, and upon the accumulation of the motion
signal within the groups of dots, especially when the direction of themotion is complex.

"A model for explaining the anomalous motion
illusion"
Masanori Idesawa(UEC Museum of Communications, UEC Tokyo (University ofElectro-Communications), Japan)

Abstract:
Anomalous motion illusion observed in still figures and in swinging
figures is a fascinating topic in the study of the human visual systemand one which attract strong interest from not only scientists but
also artists, image creators and CG researchers. Many models for
explaining the anomalous motion illusion have been proposed,
however, none of them could explain the phenomena consistently.
Almost all of them are relied only on the mechanisms in corticalsystem and disregarding the features of retinal mechanisms.
A potential model to explain the anomalous motion illusion isproposed by postulating the retinal features such as the retinal
visual reset ( periodical ground level renewing ), the spatial filteringand the response time differences between stimulation andrelaxation in retinal image forming; moreover, the features incortical system such as the velocity threshold and the apparent
motion perception are taking in account; then almost all of thefeatures of anomalous motion perception can be explained andsimulated successfully. It is considered that the postulated features
are physiologically plausible and a similar mechanism is expected in
the human visual system; the proposed model can provide new
insights that can contribute to revealing the mechanism of theanomalous motion illusion and to elucidating the human visualsystem.
In this talk I will introduce the proposed model in detail including thesupporting evidences of the postulated features; then show theseveral examples of simulated results.

"Illusions appearing in aftereffects"
Hiroyuki Ito(Faculty of Design, Kyushu University, Japan)

Abstract:
In this talk, I will demonstrate some illusions in relation to perceptual
adaptation. 1. After viewing a visual object with steady fixation, its
negative image is seen as an afterimage. However, after viewing acircle, a hexagon is seen as an afterimage and vice versa. I suggestthat the phenomenon is caused by mutual inhibition between
curvature and corner detectors. 2. "Enigma" causes an illusory
stream with some flicker impressions in the rings on the radial
pattern. When the Enigma stimulus is rotated, the perceptual flicker
ceases and an illusory stream arises in a direction that is opposite to
the physical rotation. Steady fixation on the center of the rotating
Enigma stimulus causes an illusory stream in the same direction as
the previous physical rotation after the rotation stops. Dr.
Tomimatsu and I suggest that relative motion detectors areresponsible for the phenomenon. 3. Finally, I will demonstrate some
additional illusions that are related to the present talk, including thepursuit-pursuing illusion and motion aftereffect appearing inafterimages.

"Filling in illusory appearances"
Rob van Lier (Donders Institute for Brain, Cognition andBehaviour,Radboud University Nijmegen, The Netherlands)
Abstract:
Visual illusions provide a unique window on brain processes thattransform the eye's retinal signals into a 3D world full of colors andforms. A remarkable aspect of vision is its capacity to fill in visualproperties for which no direct evidence is present in the retinal image.
This filling-in process may result in percepts with varying degrees of'phenomenological presence' - ranging from actually seeing thefilled-in properties (as with neon color filling-in), to merely assuming
the presence of these properties (as with the perception of certain

partly occluded objects). In this talk, I will review recent studies on
various illusory appearances, with a focus on so-called modal andamodal filling-in phenomena, and discuss how they help tounderstand the underlying mechanisms of perception.

"What is shape? New phenomena in the light of anew approach"Baingio Pinna (Dept. of Humanities and Social Sciences, Universityof Sassari, Italy)
Abstract:
The aim of this work is to answer the following questions: what isshape? What is its meaning? Shape perception and its meaning werestudied starting from the square/ diamond illusion and according to
the phenomenological approach traced by gestalt psychologists. The
role of frame of reference in determining shape perception wasdiscussed and largely weakened or refuted in the light of a highnumber of new illusions, based on some phenomenal meta-shapeproperties useful and necessary to define the meaning of shape.
These effects are based on the accentuation of some meta-shapeattributes. The phenomenal results demonstrate that theaccentuation of the meta-shape properties operates like Euclidean
vectors. On the basis of these results we suggest that the meaning ofshape could be understood on the basis of a multiplicity ofmeta-shape attributes operating like meaningful primitives of thecomplex language of shape perception.

"The concept of illusion and a new classification"
Brian Rogers(Department of Experimental Psychology, University of Oxford,Oxford, UK.
Department of Psychology, St Petersburg State University, StPetersburg, Russia)
Abstract:

The idea that our perceptions can be incorrect can be traced back to
the ancient Greeks. In the 11th century, Al-Haytham drew a
distinction between errors of sight (illusions) in "pure sensation", in"recognition" and in "inference". More recently, Gregory (1994) has
made a similar distinction between three causes of illusions "physical", "physiological" and "cognitive". Robinson (1972)
attempted to group illusions according to the sensory dimension
involved e.g. movement, depth, brightness and shape. What thesedifferent classifications have in common is that they all assume there
is meaningful distinction between those aspects of perception welabel as 'illusory' and those labelled 'veridical'. However, thisassumes there is an appropriate way to define the 'physical reality'
used to assess the veridicality our perceptions. I would like to argue
that there is no meaningful way of distinguishing between thoseperceptual effects we label as 'illusory' and those labelled as'veridical' - all of our perceptions depend on the particularcharacteristics of the underlying mechanisms. As a consequence, I
would like to propose a new way of classifying perceptual effects thatis based on a set of characteristics common to all perceptual
mechanisms.

"The dual role of perceptual boundaries asunifiers and dividers"

Sergio Roncato(Dipartimento di Psicologia Generale, Universita di Padova, Italia)
Abstract:
The dual role of perceptual boundaries as unifiers and dividers
The organization of the perceptual world results from the interactionof the visual units at different complexity levels. Here the exploration
is focused on a particular set of interactions that arise when dark andlight surfaces are perceived against a midgrey background. In these
conditions illusory distorting effects are often observed in the form oforientation misperception, apparent motion, misalignment. When alight and a dark edge are drawn close nearby, both the geometricand the photometric dimensions may be altered: the edges tend toillusory conjoin and the brightness of the surround is misperceived.

In a pattern where collinear, or near to colinearity edges, alternate incontrast polarity the events may replicate several times giving rise
to illusory contours.
These ones interact in different ways with similar integrated units
that origin in the same space or in proximity. On the lights of theseinteractions the events are retraced that underpin the formation ofcomplex perceptual patters such those split into different layers: forexample an opaque surface seen behind a translucent film. The
visual system once again demonstrate its �gability�h as a problem
solver.

"Illusions generated by conflicts between color,color contrast, spatial scale and position."
Arthur Shapiro(American University Washington D.C., USA)

Abstract:
Many visual phenomena illustrate that the perceived appearance of avisual object depends on the context in which the object is presented.
Explanations of such phenomena, however, concentrate on the colorof the object while giving little attention to the perceived contrast of
the object relative to the background. Here I will present a class ofvisual stimuli ("contrast asynchronies") that uses temporal phase to
separate the perception of color from the perception of color contrast(Shapiro, 2008; journalofvision.org/8/1/8). Experiments withcontrast asynchronies have led to a model of color vision that posits
separate color and color contrast pathways, and to the creation ofmany dramatic visual demonstrations. The principle behind contrast
asynchronies can be generalized to create illusions concerning theinterpretation of spatial scale, to novel variants of motion illusions,and to illusions related to spatial organization and perceptual binding.
I will show that most simultaneous contrast illusions (such as
Adelson's checker shadow and snake/anti-snake illusion) can be
accounted for by the reduction of blur, suggesting that manybrightness illusions arise because the parts of the visual system that
encode brightness act like an adaptive high-pass filter that removes
low spatial frequency content from the visual image.

"Being a (visual) illusionist: works and a future."
Kohske Takahashi(Research Center for Advanced Science and Technology, theUniversity of Tokyo, Japan)

Abstract:
Discovering, creating, and developing a novel illusion is absolutely agreat pleasure for all people who are attracted by the enigma ofbrain as well as all vision scientists. Thus far, I have discovered aseries of novel visual illusions, blurry heart illusion, scintillating
lustre induced by radial fins, chroma-achroma substitution,
expansion/contraction blindness, and approaching by frequency
modulation. In this talk, I will briefly introduce a part of these lovely
illusions, speculating the underlying mechanisms and disclosing how
I discovered them. The experiences as an illusionist have taught me
the possibilities and powers of illusions as a bridge between thevision science and the general public. At the end of this talk I will
discuss some ideas and technologies to enjoy illusion works andbuild a wonderful bridge.

"A computational model of luminance contrast
orientation illusions"

Dejan Todorović(Laboratory of Experimental Psychology, Department of Psychology,University of Belgrade, Serbia)
Abstract:
Illusions are usually defined as cases of discrepancy of ourperception from reality. This definition has problems, but it can beamended to cover many classical visual illusions reasonably well.
Illusions of orientation are cases of discrepancy of real and perceivedorientation, such as when horizontal lines are seen as tilted. Oneclass of such illusions includes a variety of figures in which the same
geometric design may or may not exhibit a tilt illusion, depending on

the luminance contrast of some of its elements. Such figures wereintroduced by Munsterberg, Fraser, Gregory and Heard, Kitaoka,Pinna, Roncato and others. Building on work by previous authors, I
will present a simple computational model of this class of illusions,based on well-known features of cells located in the early cortical
portions of the visual neural system. Simulations of the reactions of
the model to a variety of figures exhibiting impressions of illusory tilt
reveal the presence of specific patterns of neural activity
distributions, which are also present in simulations of reactions tofigures involving real tilt. Such patterns are not present insimulations of reactions to figures with the same geometry as
illusory figures but with different luminance contrasts, which do notevoke illusory tilt impressions.

TALKS"Color-dependent motion illusions in stationary
images: What causes illusory motion?"
Akiyoshi Kitaoka(Department of Psychology, Ritsumeikan University, Japan)

Abstract:
Fraser and Wilcox (1979) presented a motion illusion in a stationary
image and Kitaoka and Ashida (2003) devised a new pattern toenhance the illusion. "Rotating snakes" is one of the applied works.
Although the Fraser-Wilcox illusion chiefly depends on luminance, itscolor-dependent variant was suggested by Kitaoka (2010). The
color-dependent Fraser-Wilcox illusion is produced with acombination of four elemental parts: long-wavelength part,short-wavelength part, dark part, and bright part. Kitaoka andYanaka (2013) reported that the direction of illusory motion isreversed under a dim or dark illumination, suggesting a critical roleof rods. These studies were published and discussed in Kitaoka

(2014). The present talk reports further progress in the study on thecolor-dependent motion illusion.

"Depth illusion due to rectangularity preference"
Kokichi Sugihara(Meiji Institute for Advanced Study of Mathematical Sciences, Meiji
University, Japan)

Abstract:
There is a class of pictures called "pictures of impossible objects".
They evoke impressions of three-dimensional structures in our mind,
but at the same time make us to feel that those structures cannot beconstructed in the real world. From a mathematical point of view, on
the other hand, the structures represented by those pictures are notnecessarily impossible; some of them can be realized as
three-dimensional solids. The sense of impossibility can be explainedby a rectangularity-preference hypothesis, that is, we preferrectangular interpretations of retinal images to other interpretations.
Once we accept this hypothesis, we can not only explain the depthillusion phenomena, but also can design solids that evoke various
kinds of new illusions, such as solids that appear impossible, solids
that generate impossible motions, and solids that look quite different
when seen from different viewpoints. In this talk I will show
examples of those depth illusions, and will present a systematic
methods to design such illusions.
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