More Visual Illusions

I like visual illusions – though I must admit that the rotating snakes (Figure 1) from Professor Akiyoshi Kitaoka’a illusion pages makes me feel somewhat queasy.

Figure 1 Rotating snakes from Akiyoshi’s illusion pages (click on the image for a larger version or got to to see the illusion in all its glory).

You can find other versions of this illusion and many others at Akiyoshi’s illusion pages here, along with research papers that discuss the psychological basis of the illusions he features. An fMRI study of the above illusion is Kuriki I, Ashida H, Murakami I, and Kitaoka A 2008 Functional brain imaging of the Rotating Snakes illusion by fMRI, Journal of Vision 8 (10): 16, 1-10, and can be accessed here.

The Daily Cognition has twenty visual illusions here. presents a study of illusions from 1922 – Matthew Luckiesh’s Visual Illusions: Their Causes, Characteristics and Applications – in its entirety.

An interesting introduction to the role of visual illusions in psychological research is David Eagleman’s article on how the study of visual illusions has guided neuroscience research: Eagleman DM 2001 Visual illusions and neurobiology, Nature Reviews Neuroscience 2: 920-926.

Richard Gregory, who died in May of last year, conducetd a large amount of research on visual perception and illusions, and the website dedicated to his memory – and featuring some of his papers on illusion and perception – can be accessed here.

Another researcher in visual illusions is Cornelia Fermüller, and her website can be found here, and includes examples of illusions and her research on a computational theory of optical illusions in video sequences and stereo images. One paper worth reading is Ogale AS, Fermüller C, and Aloimonos Y 2005  Motion segmentation using occlusions, IEEE Transactions on Pattern Analysis and Machine Intelligence 27 (6): 988-992.

We examine the key role of occlusions in finding independently moving objects instantaneously in a video obtained by a moving camera with a restricted field of view. In this problem, the image motion is caused by the combined effect of camera motion (egomotion), structure (depth), and the independent motion of scene entities. For a camera with a restricted field of view undergoing a small motion between frames, there exists in general a set of 3D camera motions compatible with the observed flow field even if only a small amount of noise is present, leading to ambiguous 3D motion estimates. If separable sets of solutions exist, motion-based clustering can detect one category of moving objects. Even if a single inseparable set of solutions is found, we show that occlusion information can be used to find ordinal depth, which is critical in identifying a new class of moving objects. In order to find ordinal depth, occlusions must not only be known, but they must also be filled (grouped) with optical flow from neighboring regions. We present a novel algorithm for filling occlusions and deducing ordinal depth under general circumstances. Finally, we describe another category of moving objects which is detected using cardinal comparisons between structure from motion and structure estimates from another source (e.g., stereo).

This paper from Alex Holcombe looks at the illusion of motion perception in the cinema:

Holcombe AO 2009 Seeing slow and seeing fast: two limits on perception, Trends in Cognitive Neuroscience 13 (5): 216-221. [This paper contains links to movies as part of the paper’s supplementary materials].

Video cameras have a single temporal limit set by the frame rate. The human visual system has multiple temporal limits set by its various constituent mechanisms. These limits seem to form two groups. A fast group comprises specialized mechanisms for extracting perceptual qualities such as motion direction, depth and edges. The second group, with coarse temporal resolution, includes judgments of the pairing of color and motion, the joint identification of arbitrary spatially separated features, the recognition of words and high-level motion. These temporally coarse percepts might all be mediated by high-level processes. Working at very different timescales, the two groups of mechanisms collaborate to create our unified visual experience.

Mel Slater’s paper looks at why we experience a sense of immersion in artificially created environments.

Slater M 2009 Place illusion and plausibility can lead to realistic behaviour in immersive virtual environments, Philosophical Transactions of the Royal Society B 364 (1535): 3549-3557.

In this paper, I address the question as to why participants tend to respond realistically to situations and events portrayed within an immersive virtual reality system. The idea is put forward, based on the experience of a large number of experimental studies, that there are two orthogonal components that contribute to this realistic response. The first is ‘being there’, often called ‘presence’, the qualia of having a sensation of being in a real place. We call this place illusion (PI). Second, plausibility illusion (Psi) refers to the illusion that the scenario being depicted is actually occurring. In the case of both PI and Psi the participant knows for sure that they are not ‘there’ and that the events are not occurring. PI is constrained by the sensorimotor contingencies afforded by the virtual reality system. Psi is determined by the extent to which the system can produce events that directly relate to the participant, the overall credibility of the scenario being depicted in comparison with expectations. We argue that when both PI and Psi occur, participants will respond realistically to the virtual reality.

A different approach to the nature of immersion in visual perception of animated images can be found in this paper from Kenny Chow and Fox Harrell:

Chow KKN and Harrell DF 2009 Material-based imagination: embodied cognition in animated images, Cognition and Creativity, Digital Arts and Culture 2009, Arts Computation Engineering, UC Irvine, California,;jsessionid=A526BE7A0733A59BB004CD0AC05A9EB6.

Drawing upon cognitive science theories of conceptual blending and material anchors, as well as recent neuroscience results regarding mirror neurons, we argue that animated visual graphics, as embodied images whose understanding relies on our perceptual and motor apparati, connect both material and mental notions of images. Animated visual images mobilize a reflective process in which material-based imaginative construction and elaboration can take place. We call this process as “material-based imagination,” in contrast to the general notion of imagination as purely a mental activity. This kind of imagination is pervasive in today’s digitally mediated environments. By analyzing a range of digital artifacts from computer interfaces to digital artworks, we show the important role of imaginative blends of concepts in making multiple levels of meaning, including visceral sensation and metaphorical narrative imagining, to exemplify expressiveness and functionality. The implications of these analyses collectively form a step toward an embodied cognition approach to animation phenomena and toward recentralizing understanding of artistic and humanistic production in cognitive research.

Finally, the 2011 finalists for the Illusion of the Year contest can be found here.


About Nick Redfern

I graduated from the University of Kent in 1998 with a degree in Film Studies and History, and was awarded an MA by the same institution in 2002. I received my Ph.D. from Manchester Metropolitan University in 2006 for a thesis title 'Regionalism and the Cinema in the United Kingdom, 1992 to 2002.' I have taught at Manchester Metropolitan University and the University of Central Lancashire. My research interests include regional film cultures and industries in the United Kingdom; cognition and communication in the cinema; anxiety in contemporary Hollywood cinema; cinemetrics; and film style and film form. My work has been published in Entertext, the International Journal of Regional and Local Studies, the New Review of Film and Television Studies, Cyfrwng: Media Wales Journal, and the Journal of British Cinema and Television.

Posted on May 5, 2011, in 3-D Cinema, Cognitive Film Theory, Film Studies, Film Technology, Film Theory, Visual illusions and tagged , , , , . Bookmark the permalink. 1 Comment.

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