Memories May Skew Visual Perception

Memories May Skew Visual Perception

  6:46:00 PM    Science Lover

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Taking a trip down memory lane while you are driving could land you in a roadside ditch, new research indicates. Vanderbilt University psychologists have found that our visual perception can be contaminated by memories of what we have recently seen, impairing our ability to properly understand and act on what we are currently seeing.

aking a trip down memory lane while you are driving could 
land you in a roadside ditch, new research indicates. 
(Credit: © yellowj / Fotolia)

"This study shows that holding the memory of a visual event in our mind for a short period of time can 'contaminate' visual perception during the time that we're remembering," Randolph Blake, study co-author and Centennial Professor of Psychology, said.

"Our study represents the first conclusive evidence for such contamination, and the results strongly suggest that remembering and perceiving engage at least some of the same brain areas."

The study, led by research associate Min-Suk Kang, was recently published in the journal Psychonomic Bulletin & Review.

"There are numerous instances where we engage in visually guided activities, such as driving, while rehashing visual events in our mind's eye. Common sense tells us that this mental replay is harmless in that it does not interfere with our ability to register and react to objects within our visual field," Kang and his co-authors wrote. "Evidently, however, that is not always true when the contents of our working memories overlap with the contents of our perceptual world."

Illusion offers clues

In this study, the researchers used a visual illusion called motion repulsion to learn whether information held in working memory affects perception. This illusion is produced when two sets of moving dots are superimposed, with dots in one set moving in a different direction from those in the other set. Under these conditions, people tend to misperceive the actual directions of motion, and perceive a larger difference between the two sets of motions than actually exists.



Ordinarily this illusion is produced by having people view both sets of motion at the same time. Kang and colleagues set out to determine if the illusion would occur when one set of motions, rather than being physically present, was held in working memory.

In the experiment, participants were shown a random pattern of dots and were asked to remember the direction in which the dots were moving. They were then were shown a second pattern of moving dots. They were asked to report on the direction of second dots' movement.

The research subjects' reports of the second dots' movement was exaggerated and influenced by what they had previously seen. If they were first shown dots moving in one direction and later shown dots moving in a slightly counterclockwise direction relative to the first presented dots, they reported the counterclockwise movement to be more dramatic than it had actually been.

"We find that observers misperceive the actual direction of motion of a single motion stimulus if, while viewing that stimulus, they are holding a different motion direction in visual working memory," the authors wrote.

The results provide further support for previous findings by Vanderbilt researchers Frank Tong and Stephanie Harrison that the contents of working memory may be represented in early visual areas in the brain, including the primary visual cortex, that were previously thought to play no role in higher cognitive functions such as memory.

"Our findings provide compelling evidence that visual working memory representations directly interact with the same neural mechanisms involved in processing basic sensory events," Kang and his colleagues wrote.

Kang and Blake's co-authors were research associate Sang Wook Hong and Assistant Professor of Psychology Geoffrey Woodman. Funding from the National Institutes of Health, the National Science Foundation and the World Class University Initiative of the National Research Foundation of Korea and the Ministry of Education, Science and Technology supported the research.

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Parts of Brain Can Switch Functions: In People Born Blind, Brain Regions That Usually Process Vision Can Tackle Language

Parts of Brain Can Switch Functions: In People Born Blind, Brain Regions That Usually Process Vision Can Tackle Language

  9:52:00 AM    Science Lover

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When your brain encounters sensory stimuli, such as the scent of your morning coffee or the sound of a honking car, that input gets shuttled to the appropriate brain region for analysis. The coffee aroma goes to the olfactory cortex, while sounds are processed in the auditory cortex.

MRI scan of brain. (Credit: iStockphoto)

 

That division of labor suggests that the brain's structure follows a predetermined, genetic blueprint. However, evidence is mounting that brain regions can take over functions they were not genetically destined to perform. In a landmark 1996 study of people blinded early in life, neuroscientists showed that the visual cortex could participate in a nonvisual function -- reading Braille.

Now, a study from MIT neuroscientists shows that in individuals born blind, parts of the visual cortex are recruited for language processing. The finding suggests that the visual cortex can dramatically change its function -- from visual processing to language -- and it also appears to overturn the idea that language processing can only occur in highly specialized brain regions that are genetically programmed for language tasks.

"Your brain is not a prepackaged kind of thing. It doesn't develop along a fixed trajectory, rather, it's a self-building toolkit. The building process is profoundly influenced by the experiences you have during your development," says Marina Bedny, an MIT postdoctoral associate in the Department of Brain and Cognitive Sciences and lead author of the study, which appears in the Proceedings of the National Academy of Sciences the week of Feb. 28.

Flexible connections

For more than a century, neuroscientists have known that two specialized brain regions -- called Broca's area and Wernicke's area -- are necessary to produce and understand language, respectively. Those areas are thought to have intrinsic properties, such as specific internal arrangement of cells and connectivity with other brain regions, which make them uniquely suited to process language.

Other functions -- including vision and hearing -- also have distinct processing centers in the sensory cortices. However, there appears to be some flexibility in assigning brain functions. Previous studies in animals (in the laboratory of Mriganka Sur, MIT professor of brain and cognitive sciences) have shown that sensory brain regions can process information from a different sense if input is rewired to them surgically early in life. For example, connecting the eyes to the auditory cortex can provoke that brain region to process images instead of sounds.

Until now, no such evidence existed for flexibility in language processing. Previous studies of congenitally blind people had shown some activity in the left visual cortex of blind subjects during some verbal tasks, such as reading Braille, but no one had shown that this might indicate full-fledged language processing.

Bedny and her colleagues, including senior author Rebecca Saxe, assistant professor of brain and cognitive sciences, and Alvaro Pascual-Leone, professor of neurology at Harvard Medical School, set out to investigate whether visual brain regions in blind people might be involved in more complex language tasks, such as processing sentence structure and analyzing word meanings.

To do that, the researchers scanned blind subjects (using functional magnetic resonance imaging) as they performed a sentence comprehension task. The researchers hypothesized that if the visual cortex was involved in language processing, those brain areas should show the same sensitivity to linguistic information as classic language areas such as Broca's and Wernicke's areas.

They found that was indeed the case -- visual brain regions were sensitive to sentence structure and word meanings in the same way as classic language regions, Bedny says. "The idea that these brain regions could go from vision to language is just crazy," she says. "It suggests that the intrinsic function of a brain area is constrained only loosely, and that experience can have really a big impact on the function of a piece of brain tissue."

Bedny notes that the research does not refute the idea that the human brain needs Broca's and Wernicke's areas for language. "We haven't shown that every possible part of language can be supported by this part of the brain [the visual cortex]. It just suggests that a part of the brain can participate in language processing without having evolved to do so," she says.

Redistribution

One unanswered question is why the visual cortex would be recruited for language processing, when the language processing areas of blind people already function normally. According to Bedny, it may be the result of a natural redistribution of tasks during brain development.

"As these brain functions are getting parceled out, the visual cortex isn't getting its typical function, which is to do vision. And so it enters this competitive game of who's going to do what. The whole developmental dynamic has changed," she says.

This study, combined with other studies of blind people, suggest that different parts of the visual cortex get divvied up for different functions during development, Bedny says. A subset of (left-brain) visual areas appears to be involved in language, including the left primary visual cortex.

It's possible that this redistribution gives blind people an advantage in language processing. The researchers are planning follow-up work in which they will study whether blind people perform better than sighted people in complex language tasks such as parsing complicated sentences or performing language tests while being distracted.

The researchers are also working to pinpoint more precisely the visual cortex's role in language processing, and they are studying blind children to figure out when during development the visual cortex starts processing language.
 

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Same Face May Look Male or Female, Depending on Where It Appears in a Person's Field of View

Same Face May Look Male or Female, Depending on Where It Appears in a Person's Field of View

  9:42:00 AM    Science Lover

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Neuroscientists at MIT and Harvard have made the surprising discovery that the brain sees some faces as male when they appear in one area of a person's field of view, but female when they appear in a different location.

Neuroscientists at MIT and Harvard have made the
surprising discovery  that the brain sees some faces
as male when they appear in one area of a  person's
field of view, but female when they appear
in a different  location.

The findings challenge a longstanding tenet of neuroscience -- that how the brain sees an object should not depend on where the object is located relative to the observer, says Arash Afraz, a postdoctoral associate at MIT's McGovern Institute for Brain Research and lead author of a new paper on the work.

"It's the kind of thing you would not predict -- that you would look at two identical faces and think they look different," says Afraz. He and two colleagues from Harvard, Patrick Cavanagh and Maryam Vaziri Pashkam, described their findings in the Nov. 24 online edition of the journal Current Biology.

In the real world, the brain's inconsistency in assigning gender to faces isn't noticeable, because there are so many other clues: hair and clothing, for example. But when people view computer-generated faces, stripped of all other gender-identifying features, a pattern of biases, based on location of the face, emerges.

The researchers showed subjects a random series of faces, ranging along a spectrum of very male to very female, and asked them to classify the faces by gender. For the more androgynous faces, subjects rated the same faces as male or female, depending on where they appeared.

Study participants were told to fix their gaze at the center of the screen, as faces were flashed elsewhere on the screen for 50 milliseconds each. Assuming that the subjects sat about 22 inches from the monitor, the faces appeared to be about three-quarters of an inch tall.

The patterns of male and female biases were different for different people. That is, some people judged androgynous faces as female every time they appeared in the upper right corner, while others judged faces in that same location as male. Subjects also showed biases when judging the age of faces, but the pattern for age bias was independent from the pattern for gender bias in each individual.

Sample size
 
Afraz believes this inconsistency in identifying genders is due to a sampling bias, which can also be seen in statistical tools such as polls. For example, if you surveyed 1,000 Bostonians, asking if they were Democrats or Republicans, you would probably get a fairly accurate representation of these percentages in the city as a whole, because the sample size is so large. However, if you took a much smaller sample, perhaps five people who live across the street from you, you might get 100 percent Democrats, or 100 percent Republicans. "You wouldn't have any consistency, because your sample is too small," says Afraz.

He believes the same thing happens in the brain. In the visual cortex, where images are processed, cells are grouped by which part of the visual scene they analyze. Within each of those groups, there is probably a relatively small number of neurons devoted to interpreting gender of faces. The smaller the image, the fewer cells are activated, so cells that respond to female faces may dominate. In a different part of the visual cortex, cells that respond to male faces may dominate.

"It's all a matter of undersampling," says Afraz.

Michael Tarr, codirector of the Center for the Neural Basis of Cognition at Carnegie Mellon University, says the findings add to the growing evidence that the brain is not always consistent in how it perceives objects under different circumstances. He adds that the study leaves unanswered the question of why each person develops different bias patterns. "Is it just noise within the system, or is some other kind of learning occurring that they haven't figured out yet?" asks Tarr, who was not involved in the research. "That's really the fascinating question."

Afraz and his colleagues looked for correlations between each subject's bias pattern and other traits such as gender, height and handedness, but found no connections.

He is now doing follow-up studies in the lab of James DiCarlo, associate professor of neuroscience at MIT, including an investigation of whether brain cells can be recalibrated to respond to faces differently.

Admin's Note: This article is not intended to provide medical advice, diagnosis or treatment.

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Brain Regions Can Switch Functions in Young

Brain Regions Can Switch Functions in Young

  1:52:00 AM    Science Lover

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A new paper from MIT neuroscientists, in collaboration with Alvaro Pascual-Leone at Beth Israel Deaconess Medical Center, offers evidence that it is easier to rewire the brain early in life. The researchers found that a small part of the brain's visual cortex that processes motion became reorganized only in the brains of subjects who had been born blind, not those who became blind later in life.

Scientists offer evidence that it is easier to rewire the 
brain early in life. Researchers found that a small part 
of the brain's visual cortex that processes motion became
reorganized only in the brains of subjects who had been 
born blind, not those who became blind later in life.
(Credit: iStockphoto/Vasiliy Yakobchuk)

The new findings, described in the Oct. 14 issue of the journal Current Biology, shed light on how the brain wires itself during the first few years of life, and could help scientists understand how to optimize the brain's ability to be rewired later in life. That could become increasingly important as medical advances make it possible for congenitally blind people to have their sight restored, said MIT postdoctoral associate Marina Bedny, lead author of the paper.

In the 1950s and '60s, scientists began to think that certain brain functions develop normally only if an individual is exposed to relevant information, such as language or visual information, within a specific time period early in life. After that, they theorized, the brain loses the ability to change in response to new input.

Animal studies supported this theory. For example, cats blindfolded during the first months of life are unable to see normally after the blindfolds are removed. Similar periods of blindfolding in adulthood have no effect on vision.

However, there have been indications in recent years that there is more wiggle room than previously thought, said Bedny, who works in the laboratory of MIT assistant professor Rebecca Saxe, also an author of the Current Biology paper. Many neuroscientists now support the idea of a period early in life after which it is difficult, but not impossible, to rewire the brain.

Bedny, Saxe and their colleagues wanted to determine if a part of the brain known as the middle temporal complex (MT/MST) can be rewired at any time or only early in life. They chose to study MT/MST in part because it is one of the most studied visual areas. In sighted people, the MT region is specialized for motion vision.

In the few rare cases where patients have lost MT function in both hemispheres of the brain, they were unable to sense motion in a visual scene. For example, if someone poured water into a glass, they would see only a standing, frozen stream of water.

Previous studies have shown that in blind people, MT is taken over by sound processing, but those studies didn't distinguish between people who became blind early and late in life.

In the new MIT study, the researchers studied three groups of subjects -- sighted, congenitally blind, and those who became blind later in life (age nine or older). Using functional magnetic resonance imaging (fMRI), they tested whether MT in these subjects responded to moving sounds -- for example, approaching footsteps.

The results were clear, said Bedny. MT reacted to moving sounds in congenitally blind people, but not in sighted people or people who became blind at a later age.

This suggests that in late-blind individuals, the visual input they received in early years allowed the MT complex to develop its typical visual function, and it couldn't be remade to process sound after the person lost sight. Congenitally blind people never received any visual input, so the region was taken over by auditory input after birth.

"We need to think of early life as a window of opportunity to shape how the brain works," said Bedny. "That's not to say that later experience can't alter things, but it's easier to get organized early on."

Bedny believes that by better understanding how the brain is wired early in life, scientists may be able to learn how to rewire it later in life. There are now very few cases of sight restoration, but if it becomes more common, scientists will need to figure out how to retrain the patient's brain so it can process the new visual input.

"The unresolved question is whether the brain can relearn, and how that learning differs in an adult brain versus a child's brain," said Bedny.

Bedny hopes to study the behavioral consequences of the MT switch in future studies. Those would include whether blind people have an advantage over sighted people in auditory motion processing, and if they have a disadvantage if sight is restored.

Editor's Note: This article is not intended to provide medical advice, diagnosis or treatment.

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