Bridging Abnormal Perception And Psychotic Symptoms
The reduced susceptibility to visual illusions in people with schizophrenia has been correlated with a number of psychotic symptoms, such as disorganisation . For example, in a community sample measured on their level of schizotypy, thought disorder was found to be associated with visual illusion susceptibility . This again may highlight the role of perceptual organisation in the experience of visual illusions, particularly considering the significant relationships between cognitive disorganisation symptoms and perceptual organisation that have been found . Therefore, it may be the case that the general impairment to perceptual organisation in schizophrenia mediates these correlations with the disorganisation syndrome. Further research will be needed to investigate this. However, we explain in this section how we think examining the reduced susceptibility to visual illusions may also shed light on the underpinnings of other psychotic symptoms, specifically visual distortions.
Another possible explanation to bridge symptoms and visual illusions is a Bayesian prediction approach . However, one issue with this thinking is that, in order to make Bayesian predictions, the brain must first be fed sensory input. Yet, hallucinations are generated internally and require no formal stimulus to be present in relation to their perceptual experience. In other words, there seems to be an absence of sensory input to produce this aberrant perception .
Possible Causes Of Visual Illusions
There are two main theories of perception that we will briefly explore that can explain some possible causes for why visual illusions work:
- Gibson’s The Direct Theory of Perception suggests that we perceive the world through our eyes using the information we see directly. Nature influences our perception of the world. Gibson referred to how this direct information about the world is sent to our brain from our eyes as bottom-up processing.
- Gregory’s The Constructivist Theory of Perception suggests that we use information stored in our brains from previous experiences to perceive the world around us. How we perceive the world is influenced by nurture and external factors from our environment. Gregory referred to this stored information being brought down to our visual senses for interpretation as top-down processing.
Both of these theories can explain why we fall for visual illusions because the image we see either does not match up with information that we already have stored. So it isn’t easy to interpret and understand because we automatically trust what we see in front of us as the truth.
Either way, our visual system gets easily overwhelmed and misinterprets the image.
Ebbinghaus In The Real World
Imagine that you are in a golf competition in which you are putting against someone with the same experience and skill that you have. There is one problem: Your opponent gets to putt into a hole that is 10% larger than the hole you have to use. Youd probably think that the competition was unfairly biased against you.
Now imagine a somewhat different situation. You and your opponent are about equal in ability and the holes you are using are the same size, but the hole that your opponent is using looks 10% larger than the one you are using. Would your opponent have an unfair advantage now?
If you read the earlier section on the Ebbinghaus effect, you have an idea how psychologists could exploit your perceptual system to test this very question.
Psychologist Jessica Witt and her colleagues Sally Linkenauger and Dennis Proffitt recruited research participants with no unusual golf experience to participate in a putting task. They competed against themselves rather than against another person.
The experimenters made the task challenging by using a hole with a 2-inch diameter, which is about half the diameter of the hole you will find on a golf course. An overhead projector mounted on the ceiling of their lab allowed them to project Ebbinghauss circles around the putting hole. Some participants saw the putting hole surrounded by circles that were smaller than the hole in the center the other half saw surrounding black circles that were larger.
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Use Of Visual Illusions To Alter Receivers Perspective
Illusions of size
In many cases, it is advantageous for individuals to be able to manipulate their apparent size, for example, when under threat, during malemale competition, and during courtship. When choosing a mate, animals typically compare locally available mates and make choices based on features that may signal quality, such as size and color . The perceived quality of an individual is not fixed and can be influenced by encounters with other potential mates that may be sequential or simultaneous . Theory predicts that individuals should attempt to increase their perceived attractiveness by choosing to display in a social environment that contains lower quality mates, but until recently empirical experiments have been lacking .
Ebbinghaus illusion, where the central circle appears larger when surrounded by smaller inducer objects and the same-sized target appears smaller when surrounded by larger inducers Wundt-Jastrow illusion: the lower shape looks larger than the upper shape despite them being the same size Delboeuf illusion: the central black circles are the same size, but the circle on the right looks smaller than the one on the left horizontalvertical illusion, where the vertical line looks longer than the horizontal line despite them being of equal length.
Illusions of shape
Illusions that draw the attention of receivers
Illusions of brightness and color
Illusions involving movement
How Does The Hermann Grid Illusion Work
So why do people see gray where there should be white? Why do we see something so different from reality?
Researchers have traditionally used what is known as lateral inhibition to explain why people see these gray areas. These phenomena demonstrate a very important principle of perception: we don’t always see what’s really there. Our perceptions depend upon how our visual system responds to environmental stimuli and how our brain then interprets this information.
However, there is evidence suggesting that this explanation is likely inaccurate. The fact that the illusion is not dependent upon size, can be seen with contrast reversal and can be negated by slightly distorting the lines have been cited as reasons why the classic theory is wrong. One possible explanation that has been proposed is known as the S1 simple-cell theory.
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Limitations In Previous Research
Discrepancies in results may be related to methodological issues, such as the heterogeneity of the sample . Therefore, when carrying out visual psychophysics studies in patients with schizophrenia, future research should take into account a number of potential confounding factors, including medication effects, task response types, the number of illusions tested and disease heterogeneity.
Gregory And Top Down Processing Theory
Psychologist Richard Gregory argued that perception is a constructive process which relies on top-down processing.
Stimulus information from our environment is frequently ambiguous so to interpret it, we require higher cognitive information either from past experiences or stored knowledge in order to makes inferences about what we perceive. Helmholtz called it the âlikelihood principleâ.
For Gregory perception is a hypothesis, which is based on prior knowledge. In this way we are actively constructing our perception of reality based on our environment and stored information.
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The Ames Room Illusion
Mosso – http://www.flickr.com/photos/39325045@N00/355613728/
Would you be surprised to learn that the two people in the image at the left are actually the same size? Learn more about how this classic illusion works and how the effect has been put to use in special effects such as in the movie The Lord of the Rings.
Medication As A Confounding Variable
Until the 1990s, research on cognitive deficits in schizophrenia had typically been conducted with chronically ill patient groups , with the majority of samples having significant medication and treatment exposure . Thus, the role of medication effects and illness course on visual processing should be considered. Conducting visual illusion research with individuals at an earlier stage of illness, or with those at risk of developing psychosis, may be useful in providing further insights, as this will avoid the potential confounding nature of these types of variables.
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The Hermann Grid Illusion
Rob Patrick Robpatrick / Flickr CC
Sometimes we see things that aren’t really there, and the Hermann Grid illusion is a great example of this. Notice how the dots at the center of each intersection seem to shift between white and gray? Like many optical illusions, different theories have been proposed to explain exactly why this happens.
Where The Conflict Between Perception And Reality Lies In The Brain
My colleague Sigal Samuel recently explored the neuroscience of meditation. During her reporting, she found good evidence that a regular meditation practice is associated with increased compassion. That evidence, she writes, feel like a challenge, even a dare. If it takes such a small amount of time and effort to get better at regulating my emotions … am I not morally obligated to do it?
Perception science, for me, provokes a similar question. If the science tells us our brains are making up a story about reality, shouldnt we be curious about, and even seek out the answers to, how that reality might be wrong?
Its not about doubting everything that comes through our senses. Its about looking for our blind spots, with the goal of becoming better thinkers. It can also help with empathy. When other people misperceive reality, we may not agree with their interpretation, but we can understand where it comes from.
To approach this challenge, I think it helps to know that the brain is telling us stories about the smallest things we perceive, like the motion of objects. But it also tells us stories about some of the most complex things we think about, creating assumptions about people based on race, among other social prejudices.
Lets start with the small.
The experiment included only nine participants but collected a lot of data on each of them. Each participant completed the experiment 10 times.
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Visual Deficits In Developmental Dyslexia
DD is often defined as a deficit in reading acquisition despite normal intelligence and access to conventional instruction . However, some variations in the definition of DD are present. For example, the U.S. National Institutes of Health define DD as a learning disorder . One of the worldwide used manual of medical diagnosis ICD 10 includes separate diagnoses for DD and for dyslexia and alexia. The latest version of the U.S. manual of psychiatric diagnosis , does not specifically define DD including that in a larger category called specific learning disorders.
Several attempted to account for DD, two main views, however, received major support. The first approach proposes that DD arises from deficits in systems that are specifically linguistic in nature. In particular, the phonological deficit theory suggests that DD arises from deficits in phonological processing . In contrast, many authors suggest that disorders in underlying non-linguistic sensory mechanisms are the real core deficit in DD .
This theory, known as the temporal processing hypothesis, is the multisensory version of the magnocellular dorsal theory of DD. This theory suggests that children with DD have deficits in rapid processing in visual and auditory modalities . Chiefly, the temporal processing hypothesis explicitly claims that phonological decoding deficits in dyslexics could arise from impairments in sensory processing of visual and auditory dynamic-stimuli .
Features Of Gibson’s Theory
The starting point for Gibsonâs Theory was that the pattern of light reaching the eye, known as the optic array, containing all the visual information necessary for perception
This optic array provides unambiguous information about the layout of objects in space. Light rays reflect off of surfaces and converge into the cornea of your eye.
Perception involves âpicking upâ the rich information provided by the optic array in a direct way with little/no processing involved.
Because of movement and different intensities of light shining in different directions it is an ever changing source of sensory information. Therefore, if you move, the structure of the optic array changes.
According to Gibson, we have the mechanisms to interpret this unstable sensory input, meaning we experience a stable and meaningful view of the world.
Changes in the flow of the optic array contain important information about what type of movement is taking place. The flow of the optic array will either move from or towards a particular point.
If the flow appears to be coming from the point, it means you are moving towards it. If the optic array is moving towards the point you are moving away from it.
the optic array contains invariant information that remains constant as the observer moves. Invariants are aspects of the environment which donât change. They supply us with crucial information.
Two good examples of invariants are texture and linear perspective.
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Color And Brightness Constancies
Perceptual constancies are sources of illusions. Color constancy and brightness constancy are responsible for the fact that a familiar object will appear the same color regardless of the amount of light or color of light reflecting from it. An illusion of color difference or luminosity difference can be created when the luminosity or color of the area surrounding an unfamiliar object is changed. The luminosity of the object will appear brighter against a black field than against a white field, even though the object itself did not change in luminosity. Similarly, the eye will compensate for color contrast depending on the color cast of the surrounding area.
In addition to the gestalt principles of perception, water-color illusions contribute to the formation of optical illusions. Water-color illusions consist of object-hole effects and coloration. Object-hole effects occur when boundaries are prominent where there is a figure and background with a hole that is 3D volumetric in appearance. Coloration consists of an assimilation of color radiating from a thin-colored edge lining a darker chromatic contour. The water-color illusion describes how the human mind perceives the wholeness of an object such as top-down processing. Thus, contextual factors play into perceiving the brightness of an object.
Visual Illusions In Developmental Dyslexia
The role of visual illusions in unveiling perceptual and attentional deficits in DD was crucial during the last 15 years. For example, Slaghuis et al. using an apparent motion Ternus display showed that individuals with DD, both children and adults, presented a significant reduction in Ternus group movement.
Pammer and Wheatley showed that individuals with DD are less sensitive to the detection of the frequency doubling illusion pattern than normal readers, supporting a low-level deficit in the M-D pathway. The FD illusion was explained by Kelly in terms of the full wave rectification carried out by the visual system. Such rectification is found in M-cells of the primate retina and LGN . It is therefore suggested, that responses from the M-cells underlie perception of the FD illusion -cells and frequency doubling).
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How Does The Ames Room Illusion Work
The effect works by utilizing a distorted room to create the illusion of a dramatic disparity in size. While the room appears square-shaped from the viewer’s perspective, it is actually has a trapezoidal shape. The woman on the right hand side of the image above is actually standing in a corner that is much further away than the woman on the left.
The illusion leads the viewer to believe that the two individuals are standing in the same depth of field when in reality the subject is standing much closer. The woman on the left in the image above appears at a much greater visual angle, but the fact that she appears to be at the same depth of field as the figure on the right makes the closer individual look much larger.
The effect can be observed in a number of films, including The Lord of the Rings trilogy. Note the early scenes in The Fellowship of the Ring where the effect is prominently used to make Gandalf appear larger than the hobbits.
You can see more examples of Ames rooms in these YouTube videos.
Evaluation Of Gibson’s Direct Theory Of Perception
Gibsonâs theory is a highly ecologically valid theory as it puts perception back into the real world. A large number of applications can be applied in terms of his theory e.g. training pilots, runway markings and road markings. Itâs an excellent explanation for perception when viewing conditions are clear. Gibsonâs theory also highlights the richness of information in optic array and provides an account of perception in animals, babies and humans.
His theory is reductionist as it seeks to explain perception solely in terms of the environment. There is strong evidence to show that the brain and long term memory can influence perception. In this case, it could be said that Gregoryâs theory is far more plausible.
Gibsonâs theory also only supports one side of the nature nurture debate, that being the nature side. Again, Gregoryâs theory is far more plausible as it suggests that what we see with our eyes is not enough and we use knowledge already stored in our brain, supporting both sides of the debate.