Visual illusions

6 Key excerpts on "Visual illusions"

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  Perceptual Illusions

  Philosophical and Psychological Essays

  • C. Calabi(Author)
  • 2017(Publication Date)
  • Palgrave Macmillan

    (Publisher)

  59 Introduction The number of phenomena that are described as illusions has greatly grown during the last two centuries, and research on illusions has become a fundamental component of psychological research about per- ception. In the use made, for instance, by Gregory (1997) “illusion” is an umbrella term for a great variety of phenomena, considered to be systematic perceptual errors occurring during inferential processes, includ- ing: ambiguities (the Necker cube, visual effects provoked by mist or retinal rivalry); distortions (classic geometric illusions, but also mirages); paradoxes (impossible figures, the mirror represented in Magritte’s “La reproduction interdite”); fictions (rainbows, galleons in the clouds, the Kanizsa triangle and after-images). However, the characterization of the notion of illusion is not uncontroversial. The (largely acknowledged) heuristic value of illusory phenomena and a neutral characterization of the notion of illusion The notion of illusion as perceptual error is especially problematic in the framework of “direct” approaches to perception, because they tend to reduce or avoid the reference to inferential processes and internal representations in the explanation of perceptual phenomena (O’Regan and Noë, 2001). The ecological approach to perception – the most criti- cal towards the notion of illusion – defines perception as the direct picking up of information in the form of invariants to movement; no inferential treatment is needed in order to transform the bare data into meaningful perceptions, thus no error can be committed – perception is 3 The Awareness of Illusions Elena Pasquinelli 60 Elena Pasquinelli by definition correct (Gibson, 1979; Stoffregen and Bardy, 2001; Turvey et al., 1981).

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  Visual Perception

  An Introduction, 3rd Edition

  • Nicholas Wade, Mike Swanston(Authors)
  • 2013(Publication Date)
  • Psychology Press

    (Publisher)

  The distinction between illusions and hallucinations has often been difficult to draw. One way of separating them is to refer to the population experiencing the phenomena. Generally speaking, visual spatial illusions are seen by everyone, albeit with different magnitudes. However, if someone says that they can see an elephant in the room, this perception may not be shared by others. Thus, hallucinations can be thought of as idiosyncratic rather than universal. This simple distinction breaks down when we consider some of the oldest descriptions of states that were called hallucinations – they were referred to as subjective visual phenomena by Purkinje. Despite the fact that many of the subjective phenomena he examined had previously been described, his contribution was to classify the observations, to describe them with precision, and interpret them within the context of the then known physiology. Purkinje’s representations of these effects are shown in Figure 2.30. He described stroboscopic patterns, pressure figures, effects of galvanic stimulation, blind spot, pattern disappearances and distortions, visibility of retinal blood vessels and blood flow, afterimages, aftereffects, single and double vision, eye movements, peripheral vision, real and apparent motion, accommodation, near and far vision, and voluntary squinting. We can take stroboscopic (flickering) patterns as an example of his approach: he produced flicker by waving his fingers in front of one eye, while looking at the bright sky, and reported seeing checkerboards, zigzags, spirals, and ray patterns. They are now referred to as stroboscopic patterns although they were described before the stroboscope was invented. When the eye is stimulated by an unpatterned, flickering light, patterns of bewildering complexity become visible. They are called stroboscopic patterns after the modern form of the instrument, which can deliver pulses of light at very high frequencies.

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  Process and the Authentic Life

  Toward a Psychology of Value

  • Jason W. Brown(Author)
  • 2013(Publication Date)
  • De Gruyter

    (Publisher)

  Illusions are not limited to those we perceive and study, but are found in all aspects of daily life. They include such fictions as object stability in a world of flux, time as linear rather than recurrent, change as an external relation between objects rather than intrinsic to the object formation and being as thing-like rather than a category that enfolds a becoming . On these foundations, the whole edifice of mind develops, and with it, the gap from self to world, the emergence of the present moment and, around it, past and future, and the feeling of intention and desire. Following Vaihinger (1924) one could add semantic class and conceptual classifications, light and dark, hot and cold, the notion of the mean, the atom, mathematical objects, archetypes, ideals, noumena, time in relation to celestial movement, and isolated instances of animals, plants or any object. Every object is a distinction, every distinction a potential class. As Wordsworth put it, We create distinctions, then Deem that our puny boundaries are things Which we perceive, and not which we have made” (Prelude II, 221). 582 Image and reality In what sense are any phenomena real , that is, physical entities or non-conceptual properties of physical nature, including the brain? The illusory is opposed to the real, but if brain process is part of physical nature, and if mind reduces to brain, mental events are equivalent to brain events, and are then illusory only if mind and brain are uncoupled. Otherwise, nature would also be illusory, and the illusory would become the real, since there would be no distinction from the non-real. Put differently, if an idea and a tree are phenomena – concepts, images, appearances – reducible to brain process, the correlated brain process could not be more real than its mental equivalents, since process and image are ultimately the same.

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  Companion Encyclopedia of Psychology

  Volume One

  • Andrew M. Colman(Author)
  • 2018(Publication Date)
  • Routledge

    (Publisher)

  transactionalists. For them perception was a transaction between observer and environment yet another twist on the empiricist theme (Kilpatrick, 1961). Results of their research can be seen in the distorted rooms and similar illusory displays to be found in many a science centre. The best known of these is a distorted room in which, from a certain vantage point, the retinal image is identical to that which would be produced by a normal "four square" room. When the room is viewed from this point, it does indeed appear normal, and we may have difficulty in being persuaded otherwise. In such a room strong illusions of size and distance can be induced. All this shows with remarkable force how easy it is to manipulate visual cues to yield non-veridical percepts. It demonstrates how much we are creatures of habit, in this case the cognitive habits induced by the properties of our stable visual surroundings.

  Our perceptual world is indeed usually very stable, yields few surprises, and is not subject to misinterpretation. No doubt this is why nonpsychologists normally pay little attention to how they perceive, and may be surprised that there is so much about perception that requires investigation and explanation. It is stable because most of our percepts are overdetermined ; visual cues are mutually consistent and are reinforced by tactile, auditory, and other information about what is in the world. Only a philosopher would question whether the object in front of us is really a solid table, or the person we're talking to a robot. The world is just too consistent for us to worry about such things. But it is still true that we take a great deal on trust. It is not difficult to break the trust, and doing so can be revealing.

  Perceptual Illusions

  Everyone is familiar with Visual illusions of different types. A small sample of the best known is shown in Figures 4 -6 . Far from being mere party amusements, these illusions can help us to understand quite a bit about perception. First, why do we call them illusions? Because, as with the distorted room, there is a discrepancy between what common sense, habit, or geometrical intuition tells us should be seen, and what we actually see. Consider the Miiller-Lyer illusion of Figure 4a . The two horizontal lines are of equal length, yet are seen as different. It has been proposed that the illusion is induced by false intimations of perspective (as in the Ponzo illusion, Figure 4e ), yet this cannot be the whole story, as other versions of the Miiller-Lyer, as in Figure 4b -d

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  Vision

  • Andrew Fabian, Janet Gibson, Mike Sheppard, Simone Weyand, Andrew Fabian, Janet Gibson, Mike Sheppard, Simone Weyand(Authors)
  • 2021(Publication Date)
  • Cambridge University Press

    (Publisher)

  A percept in the absence of an explanatory stimulus is the formal definition of a hallucination, and the term vision is, in the clinical setting 33 at least, largely taken as a shorthand for visual hallucination. For many, the term hallucination has a predominantly clinical ring to it. They see it as the hallmark of madness: after all, to perceive – in any sensory domain – objects or occurrences that the majority does not is to be fundamentally separated from reality and, therefore, likely to think and behave in irrational ways. Such perceptual experiences, and the accompanying belief systems that emerge from and accompany them, have been considered as, almost by definition, beyond comprehension [1]. Moreover, given that we experience ourselves, and our relationships to others, largely through the acceptance of shared beliefs and models, the presence of these fundamental challenges to reality profoundly affects a person’s capacity to fit comfortably into their social surroundings and the capacity of those around them to accept and empathise with them. The consequences can be, and frequently are, ostracism, isolation, and stigma. It is not always the case: a person who experiences visions may also be seen as blessed with a capacity to make contact with a deeper reality, perhaps a privileged experience of the divine or the arcane. However, this perspective too brings with it a tendency to isolate the visionary. Here, I outline a different perspective of visual hallucinations, one that is rooted in a normative view of how the visual system processes the complex patterns of visible light, the small splinter of the electro- magnetic spectrum to which we have conscious access and from which we strive to make sense of the visible world.

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  Handbook of Perception: Perceptual Processing v. 9

  • SWAINE(Author)
  • 2014(Publication Date)
  • Academic Press

    (Publisher)

  He evi-dently hopes, like so many philosophers, to find knowledge from percep-tion that is not biased by assumptions. The detailed study of illusions tells us, though, that this is a vain hope. By understanding illusions of percep-tion and errors of science, we can use departures from physical fact to discover which assumptions are accepted for deriving hypotheses from signals. Illusory perceptions are as important for understanding the ob-server as nonillusory perceptions are important for understanding the world of physics. Departures from physics are the start of journeys to understanding the mind. References Carpenter, R. H. S., & Blakemore, C. Interactions between orientations in human vision. Experimental Brain Research, 1973, 18, 287-303. Deregowski, J. B. Illusion and culture. In Illusion in nature and art. R. L. Gregory & Ε. H. Gombrich (Eds.), London: Duckworth, 1973. Pp. 161-191. Gombrich, Ε. H. Art and illusion. London: Phaidon, 1960. Gregory, R. L. Distortion of visual space as inappropriate Constancy Scaling. Nature (London), 1963, 199, 678-680. Gregory, R. L. Stereoscopic shadow images. Nature (London), 1964, 203, 1407-1408. Gregory, R. L. The intelligent eye. London: Weidenfeld and Nicolson, 1970. Gregory, R. L. Eye and brain. London: Weidenfeld and Nicolson, 1972. Gregory, R. L. The confounded eye. In R. L. Gregory & Ε. H. Gombrich (Eds.), Illusion in nature and art. London: Duckworth, 1973. Gregory, R. L. Choosing a paradigm for perception. In E. C. Carterette & M. P. Friedman (Eds.), Handbook of Perception, Vol. 1. New York: Academic Press, 1974. Gregory, R. L. Do we need cognitive concepts? In M. Gazzinaga & C. Blakemore (Eds.), Handbook of Psychobiology. New York: Academic Press, 1975. Gregory, R. L. Vision with iso-luminant colour contrast. I. A technique and observations. Perception, 1977,6, 113-119. Gregory, R. L., & Harris, J. P. Illusory contours and stereo depth. Perception & Psy-chophysics, 1974, 15 (3), 411-416. Gregory, R.

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