Color perception
February 19, 2008
Category: Color perception • Perception • Research
Take a look at this amazing illusion created by Arthur Shapiro (you'll need the latest version of Flash Player to see it):
You're looking at two donut-shaped figures whose "holes" are gradually changing color from black to white and back again. It appears that the holes are changing in an opposite pattern -- when one is light, the other is dark, and so on. But if you click to remove the surrounding donuts, you'll see that the two holes are actually changing together.
If you're still not convinced, get a friend to help. One of you looks at the light donut and the other looks at the dark donut. Then each of you says "light" when your donut hole turns light. You'll soon be saying "light" simultaneously!
Shapiro calls this the Contrast Asynchrony illusion, and he argues that it can tell us a lot about how the visual system works. Below is an interactive version of the illusion. You can manipulate all sorts of variables to change the way the illusion appears. There's even more than one way to eliminate the appearance of the illusion entirely. Can you figure out what you need to do to make the illusion disappear?
Read on »
Posted by Dave Munger at 2:22 PM • Comments (45)
September 18, 2007
Category: Color perception • Emotion • Language • Research
Take a look at this video (QuickTime required). The screen will turn white for 1/2 second. Then a word will appear for about 1.5 seconds. Pay attention to the particular shade of gray the word is printed in. Next, a strip of five different grey squares will appear. Which square matches the color of the word?
It's a difficult task, but not impossible (we'll collect answers in a poll at the end of the post). A team led by Brian P. Meier had college student volunteers complete a similar task, and they were able to achieve 30 percent accuracy -- somewhat better than the 20 percent you would expect if they were choosing randomly. But as you might guess, the researchers weren't primarily interested in how accurate the viewers were. What they wanted to know is if the word itself influenced the students' choice of color.
In 1999 the controversial linguist George Lakoff and philosopher Mark Johnson argued that metaphors used in language can actually affect our perceptions. Indeed, metaphors of "light" and "dark" are frequently used by politicians to represent good and evil. But Lakoff and Johnson's research is typically applied only to linguistic meaning. Can it also apply to visual cognition? In 2004 Meier led a team which found that viewers were faster and more accurate categorizing positive words when the letters were white, and better categorizing negative words when the letters were black.
In a new set of experiments, Meier's team wanted to see if the process worked in reverse.
Read on »
Posted by Dave Munger at 2:38 PM • Comments (8)
July 5, 2007
Category: Color perception • Language • Perception • Research
A continuation of our "greatest hits" from past Cognitive Daily postings:
[originally posted on May 9, 2006]
The Stroop Effect is one of the most-studied phenomena in psychology. The test is easy to administer, and works in a variety of contexts. The simplest way to see how it works is just to look the following two lists. Don't read them, instead say the color each word is displayed in, as quickly as you can:
If English is your native language, you should be much quicker at naming the colors of the first list than the second list. Why? Even though the task is to identify the colors, proficient readers can't stop themselves from reading the words, which slows color identification in cases where the color is different from the word.
But recently, Amir Raz and colleagues noticed that they could reduce and even eliminate the Stroop Effect by hypnotizing participants and suggesting to them that the words were in a foreign language, so they could focus solely on color. In a new experiment, Raz and three other researchers attempted to see if the hypnosis itself was necessary.
Read on »
Posted by Dave Munger at 9:54 AM • Comments (8)
July 2, 2007
Category: Color perception • Perception • Research
This is a guest post by Jonathan Leathers, one of Greta's top student writers for Spring 2007.
Take a look at this word:
MONDAY
What color do you see? Red? Blue?
While you may see nothing unusual, some people report being able to perceive colors associated with different days of the week when they are written down or heard in conversation. This ability is attributed to a phenomenon known as synesthesia, previously thought to be extremely rare. In synesthesia, the human brain interprets one set of sensory stimuli in terms of another; in other words, two senses cross. But synesthesia goes beyond metaphorically stating that one feels blue on Mondays. Previous sampling methods relied on self-referral, placing the percentage of people with synesthesia roughly around 0.05%. But, a recent study led by Julia Simner has shown that the number is actually much higher -- about 88 times higher!
There are many different forms of synesthesia, each one a product of different senses crossing -- word-color, taste-shape, music-color, people-smell -- all were included in Dr. Simner's study of synesthesia's prevalence in a population. Students at the Universities of Glasgow and Edinburgh (327 women and 173 men) were asked which, if any, forms of synesthesia applied to them by drawing a line from a list of "triggers" (smells, sounds, words etc.) to a list of corresponding "experiences" elicited (for example: colors, shapes or tastes). Those who had indicated to having some form of synesthesia, 120 in all, were then presented randomly with a trigger and instructed to record whatever they experienced. After 70 trials, the order of the stimuli would be re-randomized and each subject re-tested. After a period of several months, the students were asked to return again and complete a third test; this was done in order to ensure the consistency and validity of their answers and to verify that they were, in fact, synesthetic. Here are the results:
Read on »
Posted by Aaron Couch at 9:53 AM • Comments (44)
June 11, 2007
Category: Art • Color perception • Perception • Research
This is a guest post by Suzie Eckl, one of Greta's top student writers for Spring 2007
Forget color television.
Before we had color, we had black and white. Before we had movies, we had photographs. And before photographs we had...
Engravings?
Prior to August 19, 1839, the date Daguerre and Niepce revealed that they had created the world's first photograph, artists had all the control in reproducing the world as they saw it. Many artists chose not painting or sculpture but engraving. They carved their images into wood or burned them into metal.
In a fascinating analysis, Danielle Zavagno and Manfredo Massironi have uncovered some key differences between the techniques used by engravers and the photograph. It shouldn't be surprising that an engraving lacks certain qualities that a modern photograph would have.
Read on »
Posted by Aaron Couch at 9:54 AM • Comments (9)
May 9, 2007
Category: Attention • Color perception • Research
"I just didn't see him" is a claim that's repeated over and over in accident reports. Drivers earnestly claim that they simply didn't notice the bicycle/pedestrian/motorcycle they crashed into. The claim is made so frequently that certainly there must be a grain of truth to it. Yet it certainly isn't the case that car drivers can't see such obstacles -- after all, they can see traffic signals that are much smaller than a bike or a motorcycle.
What they mean to say is that their attention was otherwise engaged -- perhaps by a phone conversation, perhaps by other traffic, or perhaps because they were trying to find something -- a street sign, a restaurant, a gas station. Human attention is a fickle thing, and in many cases we don't notice very obvious details changing right before our eyes.
Consider the following movie (QuickTime required): One image will be displayed for a number of seconds, followed by a white screen, and then a second picture -- the same image with one very obvious detail changed. Can you spot the change (don't cheat--just watch it once!)?
Read on »
Posted by Dave Munger at 3:48 PM • Comments (42)
March 13, 2007
Category: Color perception • Memory • Perception • Research
Take a look at the image below. Your job is to find the T among the sea of Ls. If you're like most people it will take just a second or two.
Figure 1:
If you repeat this task several dozen times, each time with a new set of Ls and T in different colors, positions, and orientations, you'll get quicker at the task. Try this one -- again, look for the T.
Figure 2:
But what if a pattern was repeated later on? Would you remember it? Would you be quicker? Take a look at this figure; again, look for the T:
Figure 3:
Read on »
Posted by Dave Munger at 1:17 PM • Comments (4)
September 14, 2006
Category: Color perception • Language • Perception • Research
Color categories, as we pointed out in this post, are remarkably consistent, even across different cultures and languages. "TLTB" pointed out in the comments that for people with color blindness, the color categories might not make much sense. He brought up an excellent point, one that becomes doubly perplexing when we realize that no two individual eyes are the same -- indeed, retinal scanning is considered more accurate than fingerprints in establishing someone's true identity.
The distribution of cones and rods across the retina varies substantially. What's more, the macula, a region in the center of the retina, has a pigment that varies from individual to individual, filtering out the many of the shorter wavelengths of light before they even reach the photoreceptors on the retina -- so those signals never reach the brain. Thus, we "see" different colors in our peripheral vision than in normal vision. Finally, the lens itself has pigments which also filter out some wavelengths of light. So do individual variations in the eye affect how we categorize colors?
Take a look at this diagram to see how this filtering can affect the light reaching the receptors in your eye:
Read on »
Posted by Dave Munger at 1:34 PM • Comments (1)
September 11, 2006
Category: Color perception • Language • Research
The World Color Survey is a massive project which attempts to understand how colors are categorized in different languages. The researchers studied 110 different languages, none of which had a written component, which ensured that only spoken word categories would be used to describe the colors.
Do the speakers all understand colors the same way? Is "red" red whether you're speaking Chumburu or Saramaccan? Rolf Kuehni undertook an analysis of the data to try to find out.
To discuss colors and language, it's important to differentiate between the word we're using to describe a color, and the color itself. Color researchers use the term "gloss" to distinguish between the two. So "red gloss" is the word being used to describe the color red (which might be "rouge", "rosso", or "red"), while "red" refers to the color itself (since we're speaking English right now). In the World Color Survey, four hues were identified as unique -- red, green, yellow, and blue.
Read on »
Posted by Dave Munger at 3:41 PM • Comments (9)
July 20, 2006
Category: Color perception • Perception • Research
[article originally posted September 27, 2005]
All this talk about stereotypes can get you thinking. Perhaps some stereotypes reflect actual differences. Take color vision, for example: men often refer to themselves as "color-impaired," letting the women in their lives make home design decisions and even asking them to match clothing for them. Maybe they're just behaving in accordance with traditional stereotypes ... but maybe there's something more to it.
In the 1980s, vision researchers began to find some real physical differences between the eyes of many women and those of most men. "Normal" color vision is possible because we have three different types of cone cells in our eyes, each of which responds to a different wavelength of light. The process is basically the reverse of how a TV set or computer monitor works: on a TV, there are three different colored dots—red, green, and blue—and the millions of "colors" we see are based on mixtures of different proportions of those colors. In the eye, cone cells can have three different photopigments. These are usually generalized as red, green, and blue, but their actual values are closer to yellowish green, green, and bluish violet. To avoid confusion, psychologists typically refer to them to long-, medium, and short-wavelength sensitive cones. Supposing we're looking at a yellowish-green thing, the long-wavelength cones are stimulated the most, the medium-wavelength cones are stimulated a bit, and the short-wavelength cones are not stimulated at all, and the appropriate signal is sent along the optic nerve to the brain, which then recognizes the color as "yellowish-green."
Read on »
Posted by Dave Munger at 10:22 AM • Comments (11)
June 29, 2006
Category: Attention • Color perception • Research
One of the amazing things about the Stroop Effect is how much good research is being done based on this simple phenomenon, over 70 years later. One of the neatest recent experiments was created by Peter Wühr and Florian Waszak. I think I've created a simple animation that replicates their results. Click on the image below to bring up a short animated GIF. You'll see an image flash quickly, followed by a blank screen. As quickly as possible after the image flashes, say the color of the rectangle in front. Ignore any words printed on the rectangles; you just want to name the color of the rectangle in front. In case you don't get the idea right away (the images flash pretty quickly), the animation will repeat itself and you'll have a chance to try again.
So, which part was easier, Part 1 or Part 2? You can give your answer in the poll, below the fold.
Read on »
Posted by Dave Munger at 3:15 PM • Comments (7)
May 19, 2006
Category: Color perception • Research • Social
The Stroop Effect was originally just a language effect: we're slower identifying the color text is printed in when the words themselves name different colors. In the 81 years since the effect was first observed, it's been applied to a variety of very different phenomena. In general, the effect is explained by automatic processing: when a process is automatic, it conflicts with the desired goal and so slows processing. In fact, the Stroop Effect is so robust that researchers now use it to determine if a process is indeed automatic.
Much research has focused on the issue of whether racial bias is automatic, but a team led by Jerzy Karylowski wanted to know if racial categorization itself is automatic, so they turned to the Stroop task. Would you be slower to identify the color a person's name is printed in if it conflicts with their race, regardless of your racial bias?
Read on »
Posted by Dave Munger at 2:20 PM • Comments (13)
May 9, 2006
Category: Attention • Color perception • Language • Research
The Stroop Effect is one of the most-studied phenomena in psychology. The test is easy to administer, and works in a variety of contexts. The simplest way to see how it works is just to look the following two lists. Don't read them, instead say the color each word is displayed in, as quickly as you can:
If English is your native language, you should be much quicker at naming the colors of the first list than the second list. Why? Even though the task is to identify the colors, proficient readers can't stop themselves from reading the words, which slows color identification in cases where the color is different from the word.
But recently, Amir Raz and colleagues noticed that they could reduce and even eliminate the Stroop Effect by hypnotizing participants and suggesting to them that the words were in a foreign language, so they could focus solely on color. In a new experiment, Raz and three other researchers attempted to see if the hypnosis itself was necessary.
Read on »
Posted by Dave Munger at 4:01 PM • Comments (8)
March 16, 2006
Category: Color perception • Perception • Research • Social
A Witches' Bible states that "the sensitive is psychically aware of character qualities, or emotional or spiritual states, in the subject, and this awareness presents itself to him or her as visual phenomena." It's easy to dismiss such claims as pseudoscientific claptrap, yet there exist humans who, when presented with nonvisual stimuli such as tastes or smells, perceive visual imagery. I'm talking about the scientifically recognized condition, synesthesia. Synesthetes are people who perceive stimuli presented in one mode (often corresponding to one of the five senses) with a different mode. For example, musical tones might also be perceived as colors, or a friend might appear to have blue lips (as rendered in the photo of my son Jim at left).
Might it also be possible for a synesthete to associate emotions with visual images? British psychologist Jamie Ward believes he has found an individual (a nineteen-year-old woman whose initials are GW) with just such a condition. GW says she perceives "auras" around the faces of certain people, and when she sees or hears some words, she perceives colors (the same color always associated with the same word), which occupy her entire field of vision.
But how does Ward know GW isn't just fabricating the entire story?
Read on »
Posted by Dave Munger at 12:46 PM • Comments (8)
September 27, 2005
Category: Color perception • Perception • Research
All this talk about stereotypes can get you thinking. Perhaps some stereotypes reflect actual differences. Take color vision, for example: men often refer to themselves as "color-impaired," letting the women in their lives make home design decisions and even asking them to match clothing for them. Maybe they're just behaving in accordance with traditional stereotypes ... but maybe there's something more to it.
In the 1980s, vision researchers began to find some real physical differences between the eyes of many women and those of most men. "Normal" color vision is possible because we have three different types of cone cells in our eyes, each of which responds to a different wavelength of light. The process is basically the reverse of how a TV set or computer monitor works: on a TV, there are three different colored dots—red, green, and blue—and the millions of "colors" we see are based on mixtures of different proportions of those colors. In the eye, cone cells can have three different photopigments. These are usually generalized as red, green, and blue, but their actual values are closer to yellowish green, green, and bluish violet. To avoid confusion, psychologists typically refer to them to long-, medium, and short-wavelength sensitive cones. Supposing we're looking at a yellowish-green thing, the long-wavelength cones are stimulated the most, the medium-wavelength cones are stimulated a bit, and the short-wavelength cones are not stimulated at all, and the appropriate signal is sent along the optic nerve to the brain, which then recognizes the color as "yellowish-green."
What the researchers were finding when they actually looked at the structure of the eye is that many women—perhaps over fifty percent—possessed a fourth photopigment. Was this merely a genetic anomaly? Would the brain even be able to process this fourth input? The early research suggested that it would not. Women were no better at determining whether two very similar color patches were actually the same. They were only slightly better than men at detecting subtle spots of red light, a fact researchers attributed to individual difference.
However, Kimberly Jameson, Susan Highnote, and Linda Wasserman were not convinced by this evidence. Five- and six-year-old girls are better at naming colors than boys, and grown men are not as good at color-naming compared to women. They felt the existing measures of color sensitivity and color-matching did not capture all the differences between men and women, and devised a new experiment that they felt was more representative of real-world vision.
It's quite difficult to examine an eye to determine if it has the fourth photopigment—the process generally involves removing the eye itself. Jameson and her colleagues might have had just a bit of difficulty recruiting volunteers to participate in an experiment requiring such extreme measures, so instead they used a genetic test to determine how many different photopigments participants were likely to possess (they estimate this process to be about 90 percent accurate—biologists will recognize this as the genotype versus phenotype problem). Of 64 participants in the study, 23 were women with 4 photopigments, 15 were women with 3 photopigments, 22 were men with 3 photopigments, and 4 were men with 2 photopigments (this is commonly called "color-blindness," but most people with 2 photopigments can still distinguish between many colors).
Next, participants viewed a spectrum projected on a lucite window covered with tracing paper. Over the next hour and a half, they performed an array of tasks, including marking the edges of the visible rainbow, marking the locations of the "best example" of each of the major colors, and marking the edges of each "band" of color in the rainbow. Between each task, a camera flash was set off to mask the previous spectrum example, and the experimenter mounted a new sheet of tracing paper on the panel.
The most compelling results came from the number of spectral bands task:
| Type of participant |
Average number of spectral bands |
Number of participants |
| Four-pigment females |
10 |
23 |
| Three-pigment females |
7.6 |
15 |
| Three-pigment males and females |
7.3 |
37 |
| Two-pigment males |
5.3 |
4 |
Four-pigment females perceived significantly more bands of color than both three-pigment males and females. Further, three-pigment males and females are statistically indistinguishable, suggesting that the result is not due to some cultural difference between men and women.
So why were others unable to find significant results in a color-matching task when we see such dramatic results here? Jameson et al. suggest that there may be two (or more) different modes of seeing color, each processed differently in the brain. The brain may use the data from all four photopigments for some processes, but not for others. But this is still supposition. What's clear from this study is that the stereotype of women being better with color may reflect real differences between men and women.
Jameson, K. A., Highnote, S. M., & Wasserman, L. M. (2001). Richer color experience in observers with multiple opsin genes. Psychonomic bulletin and review, 8, 244-261.
Posted by Dave Munger at 4:09 PM • Comments (22)
June 10, 2005
Category: Color perception • Language • Perception • Research
When I was about twelve years old, I came up with an idea for a massive practical joke to play on an unsuspecting baby. For its entire childhood, everyone around the baby would conspire to convince it that the sky was green. Then at some point in the future, perhaps in front of the entire sixth grade class at Whitworth Elementary School, the truth would be revealed, and one poor kid's world would be turned upside-down.
Somehow I was never able to recruit enough people to pull this ruse off, but it does beg the question: would such a joke even be possible, or would our natural perceptual categories outweigh the influence of hundreds of tricksters? In short, do children understand the differences between colors first, or do they simply learn the names for colors without understanding what they signify? While they were probably not inspired by an idea for a practical joke, Nicola Pitchford and Kathy Mullen of McGill University were able to devise an experiment to begin to address the question ("The Development of Conceptual Colour Categories in Pre-School Children: Influence of Perceptual Categorization," Visual Cognition, 2003).
A large body of research has shown that adults categorize colors into eleven basic categories: white, black, red, green, yellow, blue, brown, purple, pink, orange, and grey. These categories have been tested extensively, even across cultures, and found to be readily identifiable by all adults. When asked to name colors across a wide spectrum of possibilities, most people use the basic color categories to describe even the colors that fall on the border between two categories.
Young children also learn these categories, but only gradually. A very young child might use the same name—say, blue—to describe a wide variety of colors (in fact, two of the 2-year-olds that Pitchford and Mullen studied used "blue" to describe all 11 colors in their study).
Pitchford and Mullen asked kids ranging from age 2 to 5 to name the color of the outfit a cartoon character was wearing. Not surprisingly, the older kids were more accurate, but most interesting was the type of errors the children made. Colors can be arranged in a color wheel (or more accurately, a three-dimensional solid). Some colors, such as orange and yellow, are closer neighbors on the color wheel than others, such as blue and red. The researchers analyzed the errors kids made naming colors and came up with the following result:
Children were sorted by language ability. Those with the ability of an average 2-year-old made the most color errors—but they made an equal number of errors for colors that were distant on the color wheel compared to adjacent colors. It's as if they simply randomly selected a color when they weren't sure about its name. By contrast, the 3-year-old language group, when they made errors, were more likely to pick adjacent colors—saying "yellow" when the color was orange, for example. While the 4-5 group was even more accurate, the few mistakes they made tended to be naming adjacent colors (the distinction between grey and brown is the most difficult, and errors are even made by some adults).
So it seems that toddlers, while able to learn the names of some colors, haven't yet developed an understanding of the relationship between colors. By the time they are three, kids have learned most of the basic colors, but they have also learned more about how the colors relate to each other. Older kids still make some mistakes, but nearly all of them are in related colors, so they're almost always in the ballpark of the correct color.
I suspect this means that my 6th-grade prank would have stopped working long before its victim even entered elementary school. Aspiring pranksters, be warned: better to stick with water balloons and dribble glasses than mess with the human perceptual system.
Posted by Dave Munger at 2:06 PM • Comments (1)
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