Tetrachromatic.

The word is just a fancy way of saying that some women seem to have four colour receptors in their eyes rather than the usual three. Actually some people also have a different set of three and this was known for some time before the discovery that quite a few women see extra colours than the rest of the population. Of course some men are missing a receptor and have only two and as a result are called colour blind. Compared to tetrachromats we are all colour blind.

Up to 50 per cent of women are tetrachromatic and can use their extra pigments in “contextually rich viewing circumstances”. For example, when looking at a rainbow, tetrachromat females can segment it into, on average, 10 different colours, whereas their trichromat brothers and sisters can see only seven, much as Isaac Newton’s red, orange, yellow, green, blue, indigo and violet. Consequently, for those special tetrachromat women, this island that they inhabit may be seen in emerald, jade, verdant, olive, lime, bottle and 34 other shades of green. Apparently, men and women do see the world differently.

{ Wobbly Universe | Continue reading }

When Jeremy Wolfe of Harvard Medical School (…) wanted to illustrate how the brain sees the world and how often it fumbles the job, he flashed a slide of Ellsworth Kelly’s “Study for Colors for a Large Wall” on the screen, and the audience couldn’t help but perk to attention. The checkerboard painting of 64 black, white and colored squares was so whimsically subtle, so poised and propulsive. We scanned every part of it, we loved it, and, whoops, time for a test.

Dr. Wolfe flashed another slide of the image, this time with one of the squares highlighted. Was the highlighted square the same color as the original, he asked the audience, or had he altered it? (…) We had gazed on Ellsworth Kelly’s masterpiece, but we hadn’t really seen it at all.

The phenomenon that Dr. Wolfe’s Pop Art quiz exemplified is known as change blindness: the frequent inability of our visual system to detect alterations to something staring us straight in the face. (…)

“The basic problem is that far more information lands on your eyes than you can possibly analyze and still end up with a reasonable sized brain,” Dr. Wolfe said. Hence, the brain has evolved mechanisms for combating data overload, allowing large rivers of data to pass along optical and cortical corridors almost entirely unassimilated, and peeling off selected data for a close, careful view.

{ NY Times | Continue reading | Pop-Art quiz }

unrelated { The Six Million Dollar Man }

At least 50 people in Kottayam district have reportedly lost their vision after gazing at the sun looking for an image of Virgin Mary.

Though alarmed health authorities have installed a signboard to counter the rumour that a solar image of Virgin Mary appeared to the believers, curious onlookers, including foreign travellers, have been thronging the venue of the ‘miracle’.

St Joseph’s ENT and Eye Hospital in Kanjirappally alone has recorded 48 cases of vision loss due to photochemical burns on the retina. “All our patients have similar history and symptoms. The damage is to the macula, the most sensitive part of retina. They have developed photochemical, not thermal, burns after continuously gazing at the sun,” Dr Annamma James Isaac, the hospital’s ophthalmologist, said.

There are quite a few people still seeking the miracle, despite the experiences of their unfortunate predecessors and strict health warnings against gazing at the sun with the naked eye.

{ DNA | Continue reading }

{ Bionic Eye Prototype | Boston Herald | full story }

A Hobart hotel guest received an unusual courier delivery on Tuesday night: a box containing a human eye. The foam box marked “Live human organs for transplant” was delivered by mistake by an unwitting taxi driver.

Hotel worker Gabriel Winner says the agitated guest brought the esky to reception early yesterday morning.

Tracking records for the consignment number on the esky confirmed Australian Air Express picked the package up in Brisbane shortly before 4pm on Tuesday. It was dropped at the hotel at 9.40 that night.

An Australian Air Express spokeswoman confirmed a “failure in an internal handover process” which meant the taxi driver was given the wrong package to deliver.

{ Mercury | Continue reading }

As a grad student in psychology in the early 1990s, Finnish psychologist Antti Revonsuo often had bad dreams. What struck him the most was how lifelike they were. (…) You move around, talk, run, interact with others, experience emotions, and feel the passage of time, just as in everyday life.

When Revonsuo began studying dreams, he asked his students to start keeping logs of their own nocturnal escapades. He noticed something striking. The dreams were filled with dangerous events, negative emotions, monsters, chases, escapes, fights, and near-death experiences. The dream world was a hellscape of danger, teeming with threatening events far more sinister than in waking life.

These weren’t the misfirings of diseased brains. Threat dreams were the norm, accounting for a staggering two-thirds of all dreams. Revonsuo discovered that we grossly underestimate the number of nightmares we have. As it turns out, we have 300 to 1,000 threat dreams per year—one to four per night. Just under half are aggressive encounters: physical aggression such as fistfights, and nonphysical aggression such as verbal arguments. The rest are about car crashes, falling and drowning, missing a meeting or a test, being lost or trapped, and being naked in public. The whole dream world seemed to have a negative bias: more negative emotions than positive ones, more nightmares than fantasy.

In the ancestral environment, Revonsuo reasoned, our dreams served to protect us, teaching us how to respond when a wild animal was chasing us or when we got lost in the forest. That was why the dream world was so filled with peril: to simulate the potential threats and prepare us to react quickly. But how could dreams help us select the optimal response, given that dream recall is so fragile? After all, we remember only a few of our dreams, and even those fade fast in the tumult of the day.

Revonsuo believes that by providing rehearsal, dreaming helps us recognize dangers more quickly and respond more efficiently. We don’t need to be aware of this rehearsal, just as you don’t have to recall exactly where you practiced your tennis serve in order to reap the rewards.

The idea that dreams are a dojo for perfecting waking activities fits well with what is already known about practice. Mental rehearsal through visualization improves skills, enhances learning, and changes the brain, polishing performance in almost any domain, from sports to piano playing.

The single most pervasive theme in dreaming is that of being chased or attacked. Just as athletes in training repeat parts of their performance, we may, in our nightmares, be attacked and chased over and over again, not to solve a particular problem but to actually practice efficient escape behavior. (…)

The dreaming brain, explains Revonsuo, scans emotional memories. When it detects a memory trace with a strong negative emotion, it constructs a nightmare around that theme. The more traumatic the event, the more intense the nightmare. The brain’s system for detecting threats is sensitive and flexible: Anything the brain tags with a strong negative charge gets thrown into the threat bin and dredged up at night.

Sometimes this system works well: Dreaming about a boy running in front of our car better prepares us should that danger crop up in real life. But sometimes the modern world throws the threat-detection mechanism out of whack: Watching horror movies can trigger nightmares about vampires, ghosts, aliens, or zombies. Such “nonsense nightmares” don’t rehearse any useful threats; they’re like an allergic reaction, says Revonsuo. Just as our immune system can mistake pollen for a pathogen and mount a defensive campaign, the threat-detection system misperceives horror movies and deploys its defenses by generating a nightmare.

{ Psychology Today | Continue reading }

artwork { Golan Levin, Opto-isolator, 2007 | paint, mechatronic circuits, acrylic, custom software, computer, ABS enclosure }

What does “OK” stand for, and where does the expression come from?

Eric Partridge says OK derives from the OK Club, which supported Martin “Old Kinderhook” Van Buren in 1840. That isn’t wrong, but it’s only half the story. (…) The letters, not to keep you guessing, stand for “oll korrect.” They’re the result of a fad for comical abbreviations that flourished in the late 1830s and 1840s.

The abbreviation fad began in Boston in the summer of 1838 and spread to New York and New Orleans in 1839. The Boston newspapers began referring satirically to the local swells as OFM, “our first men,” and used expressions like NG, “no go,” GT, “gone to Texas,” and SP, “small potatoes.”

Many of the abbreviated expressions were exaggerated misspellings, a stock in trade of the humorists of the day. One predecessor of OK was OW, “oll wright,” and there was also KY, “know yuse,” KG, “know go,” and NS, “nuff said.”

Most of these acronyms enjoyed only a brief popularity. But OK was an exception, no doubt because it came in so handy. It first found its way into print in Boston in March of 1839 and soon became widespread among the hipper element.

{ The Straight Dope | Continue reading }

animation { yugop | Nervous Matrix 02 }

About 2 years ago, researchers reported the discovery of the so-called “Halle Berry cell” in the human brain. This, and similar cells which respond selectively to other well-known celebrities, famous landmarks or categories of objects are located on the medial surface of the temporal lobe. (…)

The cells are located in the anterior hippocampus, and are likely to be involved in the formation of long-term memories. They carry out higher order processing of visual stimuli; some fire in response to several different images, while others are highly selective.

The Halle Berry cell, for example, becomes active only when different photographs of that actress was shown. The cell fired when the patient saw a photograph of the actress dressed as Catwoman, and even when just her name was presented. This cell therefore appears to encode the abstract concept of “Halle Berry”, rather than visual features which might be common to other images. (…)

Using electrodes which recorded the activity of 100 neurons simultaneously,  the researchers recorded the activity of 1,500 individual cells in 11 different epileptic patients. Confirming their previous study, the researchers found that 265 of those cells fired only in response to specific images.

One was found to fire when the patient was shown images of spiders; others fired in response to images of the leaning tower of Pisa, the Eiffel Tower, or the twin towers of the World Trade Center; yet others fired in response to pictures of Pamela Anderson, Jennifer Aniston, Denzel Washington or Saddam Hussein. (…)

The researchers developed a decoding algorithm based on the knowledge of  which cells fire in response to which stimuli, and the pattern of neural activity that occurs in response to those stimuli. Using that algorithm, they were able to predict accurately which images the patients were seeing from the activity of the cells. 

{ ScienceBlogs | Continue reading }

related { The need to look at celebrities }

Our brains can turn down our ability to see to help them listen even harder to music and complex sounds, say experts.

A US study of 20 non-musicians and 20 musical conductors found both groups diverted brain activity away from visual areas during listening tasks. Scans showed activity fell in these areas as it rose in auditory ones.

But during harder tasks the changes were less marked for conductors than for non-musicians, researchers told a Society for Neuroscience conference. (…)

Dr Bahador Bahrami, from the UCL Institute of Cognitive Neuroscience, said the study showed the difference in “brain organisation” between musicians and non-musicians.

“It demonstrates the mechanisms developed in the brain in the face of distraction. The brains of the conductors are highly tuned to tones.”

{ BBC | Continue reading }

At the age of 2, Underwood was diagnosed with retinoblastoma, a rare form of cancer that that affects about one in 5 million children. One year later, his eyes were surgically removed, to prevent the tumour from spreading throught the optic nerve and into the brain. Soon after his surgery, Underwood realized that he could use echoes to determine the positions of objects, and began to develop this “six sense.” { The Boy Who Sees Without Eyes | ScienceBlogs | YouTube }

You are reading these words right now because 600 million years ago, an aquatic animal called a Hydra developed light-receptive genes—the origin of animal vision.

It wasn’t exactly 20-20 vision back then though.

Hydras, a genus of freshwater animals that are kin to corals and jellyfish, measure only a few millimeters in diameter and have been around for hundreds of millions of years.

Scientists at the University of California, Santa Barbara studied the genes associated with vision (called opsins) in these tiny creatures and found opsin proteins all over their bodies.

Though they don’t have eyes or any specific light-receptive organs, researchers think that the light-sensing proteins concentrated in the mouth area of the Hydras help them to use light sensitivity to search out prey.

Because studies of animals that evolved earlier, such as sponges, don’t show the same light sensitivity, scientists were able to pinpoint the Precambrian date that animal vision first started to evolve.

{ NY Times | Continue reading }

image { Eye Care Foundation | AlmapBBDO, São Paulo }

How come if I stare long enough I see a reverse image?

Low-quality drugs were usually the problem when I was a kid, L., but I’m sure this is not a concern for young folks today.

Basically, there are two kinds of afterimages–negative afterimages (the kind you noticed), and complementary afterimages (i.e., red becomes green, blue becomes orange, etc.). The latter are the kind you find in intro-to-psych textbooks, where you stare at, say, a green figure for a while, then shift your eyeballs to a blank page, whereupon you see a red ghost image that last a few seconds.

Related to this are aftereffects, which usually have to do with perception of motion, orientation, and whatnot. For example, next time you’re chugging down the highway in the back of somebody’s station wagon, stare fixedly at the lane stripes receding in the distance. When the car stops, it’ll look as though the stripes are heading toward you–i.e., as if the car were backing up. Similarly, if you stare for several minutes at a set of lines that is tilted out of the vertical, a set of lines that actually is vertical will appear to be tilted in the opposite direction.

Psychologists get paid millions to dig up tidbits like this, but they’re not so hot when it comes to explaining what causes them. The best guess is that afterimages are related somehow to nerve fatigue.

{ The Straight Dope | Continue reading }

related { Negative afterimage and other visual experiments }