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Posts Tagged ‘Cognition

When Positive Thinking Leads To Financial Irresponsibility Like Compulsive Gambling

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Everyone probably has experienced one way or the other: Émile Coué meant well with his positive thinking, but created, unintentionally, a trap that leaves many a life in disaster. Looking on the bright side can lead to irresponsible financial behavior as well, reveals an article in the Journal of Consumer Research. In a series of studies, Elizabeth Cowley (University of Sydney) examines repeat gambling in the face of loss. She finds that people often engage in too much positive thinking, selectively focusing on one win among hundreds of losses when they think back on the overall experience.

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“When we want to justify engaging in an activity which could potentially be irresponsible — like gambling — we may need to distort our memory of the past to rationalize the decision,” Cowley explains. “People who have frequently spent more money than planned on gambling edit their memories of the past in order to justify gambling again.”

For example, Cowley had participants in one study play a computer game in which they could win credits with the financial equivalent of one cent per credit. Each participant played the game 300 times. Everyone experienced one big win and one big loss. But for the other 298 games, one half of the group experienced all small losses, while the other experienced all small wins.

Cowley also manipulated the distance between the big win and the big loss.

A week later, participants were surveyed for their memories of the experience. Surprisingly, Cowley found that even some losers remembered having a positive experience. If the big win and the big loss occurred far apart, losers had fond memories and indicated a willingness to spend their own money on the game.

As Cowley explains, the further apart the big win and the big loss, the easier it was for losers to isolate their memories and focus only on the positive, a “silver lining” effect.

“The tendency to segregate positive and negative events in a mixed-loss experience is based on the logic that remembering a large gain allows people to feel good even when the objective outcome was negative,” Cowley says.

Conversely, Cowley found that winners — those who experienced 298 small wins — were happier when the big win and the big loss were closer together, allowing them to lump all the games together and ignore the big loss. She termed this the “cancellation effect.”

“When the outcome of an experience including both positive and negative events results in a net gain, people look for ways to integrate positive and negative events to reduce, if not cancel, the pain associated with the negative events,” Cowley explains.

The research is the first to consider a motivated memory explanation for justifying irresponsible behavior. Apparently, positive thinking can sometimes be negative.

JOURNAL OF CONSUMER RESEARCH, Inc. • Vol. 0 •
All rights reserved. 0093-5301/2008/3501-0006$10.00
DOI: 10.1086/527267

The Perils of Hedonic Editing

Elizabeth Cowley*

Retrospective hedonic editing occurs when people combine events to frame a previous experience in its most positive light. Although reflecting positively on the past has psychological and physiological benefits, it may also be used to justify potentially irresponsible behavior. In a gambling context the consequences may be perilous. The results of study 1 show that when they have the opportunity, potentially irresponsible gamblers use hedonic editing strategies to reconstruct the past as more positive. The more positive memory provides them with evidence to support their desired outcome—playing again. The results of studies 2 and 3 reveal that the processes underlying hedonic editing include both the temporal categorization of positive and negative events and the strategic allocation of attention. Study 3 also investigates the independence of motivation and opportunity.

Written by huehueteotl

April 23, 2008 at 9:08 am

Why Fondness Makes Us Poor Judges, But Dislike Is Spot-on

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How good are we at guessing other people’s likes and dislikes? Ever bring a favorite dish to a potluck — only to watch it go uneaten? Or receive an unwelcome shock when a cherished product is discontinued for lack of sales? People have the tendency to assume the whole world likes what we like, reveals new research from the June 2008 issue of the Journal of Consumer Research. However, we don’t generalize the same way when it comes to things we hate.

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Ambiguity – Look twice, as in Magic-Eye-Images, so in buying decisions…

“The degree of false consensus depends on whether a person likes or dislikes an item,” explain Andrew D. Gershoff (University of Michigan), Ashesh Mukherjee (McGill University), and Anirban Mukhopadhyay (University of Michigan).

Participants in one study were asked to choose a movie they like. They were then asked to guess what percentage of their peers liked the movie as well. On average, people estimated that 51.2 percent of other people also liked the movie, a significant overestimate. They also estimated that only 18.2 percent of people, on average, disliked it — a reflection of the belief that more people agree with us than disagree.

In contrast, when asked to choose a movie they dislike and make the same estimate, participants were less self-centered: they thought people would agree and disagree with their opinion in roughly the same numbers.

As the researchers explain, “This finding arises from a deeper truth about the human mind, namely that things we like are seen to contain primarily good characteristics, while things we dislike are seen to contain a mix of bad, neutral, or good characteristics.”

We might even like everything about an item — except for one unforgivable, deal-breaking trait.

“This difference leads us to make more exaggerated predictions that people like the same things we do, compared to predictions that people will dislike the same things that we dislike,” the researchers add.

Another study of ice cream sundaes found that those who liked a certain flavor combination — say, mint ice cream with walnuts and hot fudge — overestimated that people would share their fondness for the sundae by 9.9 percent. Those who disliked it only overestimated that people would share their repulsion by 0.8 percent.

They conclude: “Our research indicates that decision-makers in such situations need to be highly sensitive to the danger of over-projecting their own likes, more so than their own dislikes.”

JOURNAL OF CONSUMER RESEARCH, Inc. • Vol. 33 • March 2007
All rights reserved. 0093-5301/2007/3304-0009$10.00

DOI: 10.1086/510223

Few Ways to Love, but Many Ways to Hate: Attribute Ambiguity and the Positivity Effect in Agent Evaluation

Andrew D. Gershoff

Ashesh Mukherjee

Anirban Mukhopadhyay

Recent research has identified a positivity effect in consumers’ evaluations of agents, such as friends and professional critics, who provide word-of-mouth evaluations and recommendations. Specifically, agreement with an agent on previously loved alternatives is perceived as more diagnostic of the agent’s suitability than agreement on previously hated alternatives. This article argues that the positivity effect arises from greater ambiguity about attribute ratings of hated versus loved alternatives. Three studies support this by showing that the effect is moderated by the number of attributes, the number of alternatives, and the revelation of an agent’s attribute ratings, and is mediated by attribute ambiguity.

Written by huehueteotl

April 23, 2008 at 9:04 am

Decision-making May Be Surprisingly Unconscious

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Contrary to what most of us would like to believe, decision-making may be a process handled to a large extent by unconscious mental activity. A team of scientists has demonstrated in brain scanning images how the brain might unconsciously prepare our decisions. Even several seconds before a conscious decision its outcome could be predicted from unconscious activity in the brain.

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Fig.: Brain regions (shown in green) from which the outcome of a participant’s decision can be predicted before it is made. The top shows an enlarged 3D view of a pattern of brain activity in one informative brain region. Computer-based pattern classifiers can be trained to recognize which of these micropatterns typically occur just before either left or right decisions. These classifiers can then be used to predict the outcome of a decision up to 7 seconds before a person thinks he is consciously making the decision. (Credit: John-Dylan Haynes)

This is shown in a study by scientists from the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, in collaboration with the Charité University Hospital and the Bernstein Center for Computational Neuroscience in Berlin. The researchers from the group of Professor John-Dylan Haynes used a brain scanner to investigate what happens in the human brain just before a decision is made. “Many processes in the brain occur automatically and without involvement of our consciousness. This prevents our mind from being overloaded by simple routine tasks. But when it comes to decisions we tend to assume they are made by our conscious mind. This is questioned by our current findings.”

In the study participants could freely decide if they wanted to press a button with their left or right hand. They were free to make this decision whenever they wanted, but had to remember at which time they felt they had made up their mind. The aim of the experiment was to find out what happens in the brain in the period just before the person felt the decision was made. The researchers found that it was possible to predict from brain signals which option participants would take up to seven seconds before they consciously made their decision. Normally researchers look at what happens when the decision is made, but not at what happens several seconds before. The fact that decisions can be predicted so long before they are made is a astonishing finding.

This unprecedented prediction of a free decision was made possible by sophisticated computer programs that were trained to recognize typical brain activity patterns preceding each of the two choices. Micropatterns of activity in the frontopolar cortex were predictive of the choices even before participants knew which option they were going to choose. The decision could not be predicted perfectly, but prediction was clearly above chance. This suggests that the decision is unconsciously prepared ahead of time but the final decision might still be reversible.

“Most researchers investigate what happens when people have to decide immediately, typically as a rapid response to an event in our environment. Here we were focusing on the more interesting decisions that are made in a more natural, self-paced manner”, Haynes explains.

More than 20 years ago the American brain scientist Benjamin Libet found a brain signal, the so-called “readiness-potential” that occurred a fraction of a second before a conscious decision. Libet’s experiments were highly controversial and sparked a huge debate. Many scientists argued that if our decisions are prepared unconsciously by the brain, then our feeling of “free will” must be an illusion. In this view, it is the brain that makes the decision, not a person’s conscious mind. Libet’s experiments were particularly controversial because he found only a brief time delay between brain activity and the conscious decision.

In contrast, Haynes and colleagues now show that brain activity predicts — even up to 7 seconds ahead of time — how a person is going to decide. But they also warn that the study does not finally rule out free will: “Our study shows that decisions are unconsciously prepared much longer ahead than previously thought. But we do not know yet where the final decision is made. We need to investigate whether a decision prepared by these brain areas can still be reversed.” Daring as all imaging scientists seem to be. The study shows that there is an unconscious activity antecedent or parallel to conscious decicion making. As “post hoc non est propter hoc”, this parallelism does neither mean that this unconcsious processes are the very decision making nor that they are determining the actual decision. Even the predictability of choices based on such signals does allow for such a conclusion. In the end, the researcher team, pushing a button on their MR-scan highly predictably produced MR-images. Which does not at all explain, how magnetic resonance does work…

Nature Neuroscience (13 Apr 2008), doi: 10.1038/nn.2112, Brief Communications

Unconscious determinants of free decisions in the human brain

Chun Siong Soon, Marcel Brass, Hans-Jochen Heinze, John-Dylan Haynes

There has been a long controversy as to whether subjectively ‘free’ decisions are determined by brain activity ahead of time. We found that the outcome of a decision can be encoded in brain activity of prefrontal and parietal cortex up to 10 s before it enters awareness. This delay presumably reflects the operation of a network of high-level control areas that begin to prepare an upcoming decision long before it enters awareness.

Written by huehueteotl

April 15, 2008 at 11:37 am

Irrelevant Image Of Attractive Woman Can Make A Man More Willing To Take Big Financial Risks

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Sex sells – we all knew it. Attractive women plus cool cars equal brisk sales for auto dealers as men snap up those cars, prompted—or so advertising theory goes—by the association. But is the human male really so easily swayed? Can the irrelevant image of an alluring female posing by the merchandise actually encourage a heterosexual man to purchase it?

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Possibly, according to a new study by Stanford researchers.

The study showed that when heterosexual men are exposed to positive emotional stimuli — in this case, erotic photos of a man and woman — an area of the brain associated with anticipation of reward is stimulated. In the immediate aftermath of that stimulation, men are consistently more likely to take bigger financial risks than they otherwise would, said Brian Knutson, assistant professor of psychology.

“This is the first study to demonstrate that emotional stimuli can influence financial risk-taking,” said Knutson, lead author of a paper describing the research in the current issue of NeuroReport. The hard evidence was gathered by functional magnetic resonance imaging (fMRI) of participants’ brains as they viewed photographs of positive, negative or neutral subjects and then had to quickly make a decision to choose one of two levels of financial risk in a required gamble.

Knutson and collaborator Camelia Kuhnen (who received her PhD from the Stanford Graduate School of Business in 2006 and is now assistant professor of finance at Northwestern University) had already shown in a 2005 study using fMRI that brain activity could be used to predict whether people were about to take a financial risk. When they were, an area of the brain called the nucleus accumbens showed increased activation. When they were about to choose to avoid the risk, a different area called the insula showed increased activation.

“We knew that we should be looking at [the nucleus accumbens] from the previous study. But what we didn’t know is whether we could somehow control the activation in that area by presenting some completely irrelevant stimulus,” Knutson said. “And whether that would change activation in that area and actually change behavior.”

Knutson and his colleagues studied heterosexual male undergraduate college students. The images the men viewed were intended to stimulate an emotional response. Erotic images were used to elicit a positive response, snakes and spiders to prompt a negative response, and office supplies to trigger a neutral response.

In case any of the subjects found office supplies more repellent than snakes and spiders, the researchers had the men rate each image after the scans. They then derived personalized ratings from each of the participants, which were used to make sure that whatever brain activation they observed was properly correlated with the actual emotional response of the viewer.

After viewing each image, the participants immediately had to decide whether to take the high-risk option of gambling a dollar or the low-risk option of gambling a dime. Regardless of their choice, they had a 50-50 chance of winning or losing. Knutson and his colleagues gave each man $10 to gamble with prior to entering the MRI scanner. “We wanted them to care,” Knutson said. Depending on the men’s gambles and the random outcomes, they won or lost. “We took that money back if they lost it,” he said.

“What we saw is that when they viewed the erotic pictures, the activation in their nucleus accumbens increased compared to the other stimuli, and also that they had increased activation in that region before choosing the high-risk gamble,” Knutson said.

The researchers then applied a statistical analysis to determine whether the activation in the nucleus accumbens accounted for some of the behavioral effect. “The answer was yes, at least in the case of the positive stimuli,” Knutson said. “After people had seen those erotic pictures, they tended to pick the high-risk gamble more often, especially if they had been picking the low-risk gamble before.

“The interesting finding from an economic standpoint is that these completely irrelevant stimuli, these pictures that have nothing to do with the gambles or the history of outcomes that people have experienced with these gambles, still influence behavior,” he said. “They seem to do so at least partially by influencing activation of these brain regions.”

The findings have implications for what might make emotional appeals effective or ineffective in applications ranging from advertising to finance to politics and, perhaps not surprisingly, gambling.

“If you go to the casinos, people are wearing skimpy costumes, they’re giving you free alcohol, there are bells and lights and things like that, which don’t necessarily seem related to the odds of the gambling,” Knutson said. “But these are cues that might activate brain regions that encourage risk-taking and therefore get people to gamble more.”

So does draping a seductive woman over the hood of a car in an advertisement really help sell that car?

“Well, yes and no,” Knutson said. “It may work sometimes under some conditions.”

“Our trials are happening relatively fast, changing on a second-to-second basis,” he noted. “We’re forcing people to immediately make a decision, and the emotional stimuli appear in close temporal proximity to the decision itself.

“If you have these kinds of appeals, you’d better make it easy for people to make an immediate decision. You should put them under time pressure,” he said.

Knutson emphasized that there is still ample work to be done in deciphering the effects of emotional stimuli on behavior. He plans to study women’s responses in the future, as well as to examine other types of emotional stimuli. He also intends to examine the influence of time, to see how transient or lasting the influences of various emotional stimuli might prove to be.

“This is just a first step,” he said. “It’s an existence proof that some irrelevant emotional stimuli can influence some immediate financial decisions and that we can track down one brain basis for this influence.”

Neuroreport. 19(5):509-513, March 26, 2008.

Nucleus accumbens activation mediates the influence of reward cues on financial risk taking.
Knutson, Brian; Wimmer, G. Elliott; Kuhnen, Camelia M.; Winkielman, Piotr

Abstract:
In functional magnetic resonance imaging research, nucleus accumbens (NAcc) activation spontaneously increases before financial risk taking. As anticipation of diverse rewards can increase NAcc activation, even incidental reward cues may influence financial risk taking. Using event-related functional magnetic resonance imaging, we predicted and found that anticipation of viewing rewarding stimuli (erotic pictures for 15 heterosexual men) increased financial risk taking, and that this effect was partially mediated by increases in NAcc activation. These results are consistent with the notion that incidental reward cues influence financial risk taking by altering anticipatory affect, and so identify a neuropsychological mechanism that may underlie effective emotional appeals in financial, marketing, and political domains.

Written by huehueteotl

April 7, 2008 at 3:52 pm

Damaged Brain Can Be Repaired, Study Suggests

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Scientists in the Laboratoire de Neurobiologie des Processus Adaptatifs (CNRS/Université Pierre et Marie Curie) have shown that it is possible to repair an injured brain by creating a small number of new, specifically-targeted innervations, rather than a larger number of non-specific connections. Behavioral tests have demonstrated that such reinnervation can thus restore damaged cerebral functions.

A new afference/connection (in red) which has formed contacts on a target Purkinje cell (in blue), permitting functional restoration. (Credit: Copyright Dixon Kirsty)
Brain injury in adults can cause irreparable, long-term physical and cognitive damage. However, motor and spatial functions can be recovered if undamaged neurons are stimulated to create new innervation. This type of innervation develops spontaneously after a brain injury in very young children.

Researchers had previously shown – based on injury to the neuronal pathway linking the stem to the cerebellum(1) – it was possible to induce reinnervation in young adults similar to that observed in newborn infants. This repair was rendered possible by treating the damaged cerebellum with a peptide(2) called Brain Derived Neurotrophic Factor (BDNF) which plays a role in the development and satisfactory functioning of this neuronal pathway.

In the present case, the researchers have extended the use of this model and showed that the terminals of new axons interact with the network of undamaged neuronal cells to restore their associated functions, such as synchronized movement and spatial orientation. These results demonstrate a correlation between an improvement in behavior and the degree of reinnervation in the cerebellum. Thus a small amount of correctly-targeted reinnervation makes it possible to recover fine functions such as motor and cognitive skills.

These results open promising new perspectives and make it possible to envisage using BDNF – already employed during clinical trials on the treatment of neurodegenerative conditions such as Parkinson’s disease – to repair the human brain after a cerebral lesion.

Notes:

1) This neuronal pathway is referred to as the cerebellum to Purkinje cell climbing fiber pathway and it is implicated in the coordination of movements.

2) A protein that is normally present in the brain and is involved in its development and functioning.

Brain. 2008 Apr;131(Pt 4):1099-112. Epub 2008 Feb 25.
BDNF increases homotypic olivocerebellar reinnervation and associated fine motor and cognitive skill.
Université Pierre et Marie Curie-Paris 6, Unité Mixte de Recherche (UMR) 7102-Neurobiologie des Processus Adaptatifs (NPA), Centre National de la Recherche Scientifique (CNRS), UMR 7102-NPA, F-75005 Paris, France.

Recovery of complex neural function after injury to the adult CNS is limited by minimal spontaneous axonal regeneration and/or sprouting from remaining pathways. In contrast, the developing CNS displays spontaneous reorganization following lesion, in which uninjured axons can develop new projections to appropriate target neurons and provide partial recovery of complex behaviours. Similar pathways can be induced in the mature CNS, providing models to optimize post-injury recovery of complex neural functions. After unilateral transection of a developing olivocerebellar path (pedunculotomy), remaining inferior olivary axons topographically reinnervate the denervated hemicerebellum and compensate functional deficits. Brain-derived neurotrophic factor (BDNF) partly recreates such reinnervation in the mature cerebellum. However the function of this incomplete reinnervation and any unwanted behavioural effects of BDNF remain unknown. We measured olivocerebellar reinnervation and tested rotarod and navigation skills in Wistar rats treated with BDNF/vehicle and pedunculotomized on day 3 (Px3; with reinnervation) or 11 (Px11; without spontaneous reinnervation). BDNF treatment did not affect motor or spatial behaviour in normal (control) animals. Px11-BDNF animals equalled controls on the rotarod, outperforming Px11-vehicle animals. Moreover, Px3-BDNF and Px11-BDNF animals achieved spatial learning and memory tasks as well as controls, with Px11-BDNF animals showing better spatial orientation than Px11-vehicle counterparts. BDNF slightly increased olivocerebellar reinnervation in Px3 animals and induced sparse (22% Purkinje cells) yet widespread reinnervation in Px11 animals. As reinnervation correlated with spatial function, these data imply that after injury even a small amount of reinnervation that is homotypic to correct target neurons compensates deficits in appropriate complex motor and spatial skills. As there was no effect in control animals, BDNF effectively induces this axon collateralisation without interfering with normal neuronal circuits.

Written by huehueteotl

April 7, 2008 at 8:52 am

Parents In Denial About Their Children’s Weight Problems

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In a study of 104 children under treatment for type 2 diabetes at the Vanderbilt Eskind Pediatric Diabetes Clinic, the children and their parents were surveyed about their perceptions of the child’s weight, dietary and exercise practices, as well as barriers to improving diet and exercise habits.

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Quite often, both the children and their parents underestimated the child’s weight status.

“You could argue the first step for overcoming obesity is recognition,” said Russell Rothman, M.D., assistant professor of Internal Medicine and Pediatrics at the Vanderbilt Center for Health Services Research, and senior author on the study in February’s Diabetes Care.

“This is a group that is already getting treatment for type 2 diabetes, including education about exercise and nutrition. If anything, you might expect them to be more aware about weight issues. This should send up a red flag about how challenging it is to treat obesity in this population, if many of the parents and patients in this group don’t even recognize the problem.”

The parents and children were surveyed by telephone and were asked, among other things, “do you think your child’s/your weight is very overweight, slightly overweight, about right, slightly thin or very thin.”

While 87 percent of the children surveyed were obese by the most recent Centers for Disease Control and Prevention (CDC) standards, only 41 percent of parents, and 35 percent of the children reported themselves “very overweight.” Among parents who reported their child’s weight as “about right,” 40 percent had children who actually were at or over the 95th percentile for weight and were considered obese by government standards.

Girls were more likely than boys to underestimate their weight, and parents underestimated their children’s weight more often than the children did themselves. Additionally, those who underreported weight were more likely to report a poor diet and exercise than those who correctly reported their weight status. Those with misperceptions about weight also reported more barriers to better exercise and diet behaviors.

There have been other studies showing parents and children in the general population often don’t accurately perceive weight. However, Rothman said this is the first study to examine weight perception among children with type 2 diabetes — a population that should already have been informed of their weight status and its contribution to diabetes from their health care providers.

“As health care providers we need to take a step back and realize these families need better guidance about understanding their weight status before we can convince them to make lifestyle changes to improve their health,” said Rothman, who also serves as director of the Vanderbilt Program on Effective Health Communication. “We need to do a better job as providers to work on shared communication, using more clear language, goal setting with families about key behavior changes, identifying barriers and setting realistic goals.”

Diabetes Care. 2008 Feb;31(2):227-9. Epub 2007 Nov 13.
Accuracy of perceptions of overweight and relation to self-care behaviors among adolescents with type 2 diabetes and their parents.
Health Policy and Administration, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7411, USA. asheley@unc.edu
OBJECTIVE: To examine how adolescents with type 2 diabetes and their parents/primary caregivers perceive the adolescents’ weight and the relationship of those perceptions to diet and exercise behaviors and perceived barriers to healthy behaviors. RESEARCH DESIGN AND METHODS: Interviews were conducted with adolescents and their parents about perceptions of the adolescents’ weight, diet, and exercise behaviors, as well as barriers to engaging in healthy diet and exercise behaviors. Interviews were linked with clinic records to provide BMI. RESULTS: A total of 104 parent-adolescent dyads participated. Parents and adolescents typically perceived the adolescents’ weight as less severe than it actually was. For parents and adolescents, underestimating the adolescents ‘ weight was associated with poorer diet behaviors and more perceived barriers to following healthy diet or exercise behaviors. CONCLUSIONS: Addressing misperceptions of weight by adolescents and their parents may be an important first step to improving weight in these patients.
for bodyweight perception in adults see:

 

Written by huehueteotl

March 5, 2008 at 12:14 pm

blessed are they that have not seen, and yet have believed

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Contrary to what we might think about him, Thomas was a gutsy guy. As about the blessing, we all seem to have more or less part of it: scientists at UCL (University College London) have found the link between what we expect to see, and what our brain tells us we actually saw. The study reveals that the context surrounding what we see is all important — sometimes overriding the evidence gathered by our eyes and even causing us to imagine things which aren’t really there.
The same dim vertical target rectangle centered in two different contexts is more visible in the left vague context. (Credit: Image courtesy of University College London)

The paper reveals that a vague background context is more influential and helps us to fill in more blanks than a bright, well-defined context. This may explain why we are prone to ‘see’ imaginary shapes in the shadows when the light is poor.

Eighteen observers were asked to concentrate on the centre of a black computer screen. Every time a buzzer sounded they pressed one of two buttons to record whether or not they had just seen a small, dim, grey ‘target’ rectangle in the middle of the screen. It did not appear every time, but when it did appear it was displayed for just 80 milliseconds (80 one thousandths of a second).

“People saw the target much more often if it appeared in the middle of a vertical line of similar looking, grey rectangles, compared to when it appeared in the middle of a pattern of bright, white rectangles. They even registered ‘seeing’ the target when it wasn’t actually there,” said Professor Zhaoping, lead author of the paper. “This is because people are mentally better prepared to see something vague when the surrounding context is also vague. It made sense for them to see it — so that’s what happened. When the target didn’t match the expectations set by the surrounding context, they saw it much less often.

“Illusionists have been alive to this phenomenon for years,” continued Professor Zhaoping. “When you see them throw a ball into the air, followed by a second ball, and then a third ball which ‘magically’ disappears, you wonder how they did it. In truth, there’s often no third ball – it’s just our brain being deceived by the context, telling us that we really did see three balls launched into the air, one after the other.

“Contrary to what one might expect, it is a vague rather than a bright and clearly visible context that most strongly permits our beliefs to override the evidence and fill in the blanks. In fact, a bright and clearly visible context actually overrides the evidence in the opposite direction – suppressing our ‘seeing’ of the vague target even when it is present.

“Mathematical modelling suggests that visual inference through context is processed in the brain beyond the primary visual cortex. By starting with a relatively simple experiment such as this, where visual input can be more easily and systematically manipulated, we are gaining a better understanding of how context influences what we see. Further studies along these lines can hopefully enable us to dissect the workings behind more complex and wondrous illusions.”

PLoS Computational Biology Vol. 4, No. 2, e14 doi:10.1371/journal.pcbi.0040014

Filling-In and Suppression of Visual Perception from Context: A Bayesian Account of Perceptual Biases by Contextual Influences

Zhaoping L, Jingling L 

Visual object recognition and sensitivity to image features are largely influenced by contextual inputs. We study influences by contextual bars on the bias to perceive or infer the presence of a target bar, rather than on the sensitivity to image features. Human observers judged from a briefly presented stimulus whether a target bar of a known orientation and shape is present at the center of a display, given a weak or missing input contrast at the target location with or without a context of other bars. Observers are more likely to perceive a target when the context has a weaker rather than stronger contrast. When the context can perceptually group well with the would-be target, weak contrast contextual bars bias the observers to perceive a target relative to the condition without contexts, as if to fill in the target. Meanwhile, high-contrast contextual bars, regardless of whether they group well with the target, bias the observers to perceive no target. A Bayesian model of visual inference is shown to account for the data well, illustrating that the context influences the perception in two ways: (1) biasing observers’ prior belief that a target should be present according to visual grouping principles, and (2) biasing observers’ internal model of the likely input contrasts caused by a target bar. According to this model, our data suggest that the context does not influence the perceived target contrast despite its influence on the bias to perceive the target’s presence, thereby suggesting that cortical areas beyond the primary visual cortex are responsible for the visual inferences.

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February 20, 2008 at 12:29 pm