color

Louis J. Sheehan, Esquire

For an enlightening perspective on how primates acquire color vision, consider baby monkeys. These infants' ability to recognize basic colors in different environmental settings depends on their prior exposure to a full spectrum of colors in natural light, a new study suggests.http://louis-j-sheehan.net

Although the colors in an image shift as available light intensifies or diminishes, people, as well as monkeys, usually recognize a particular hue throughout that change. For instance, an observer perceives a dog's red collar as the same color on a dark, cloudy day as on a sunny day. Scientists refer to this crucial visual adjustment as color constancy.

Prior investigations have failed to clarify whether color constancy is an innate capability of the retina's cone cells or it's acquired only with help from the brain's visual system.

Yoichi Sugita of the Neuroscience Research Institute in Tsukuba, Japan, explored color constancy in four macaque monkeys that had been raised from age 1 month to 1 year in a room illuminated by light with a highly restricted range of wavelengths, which ensured that the animals couldn't discern a normal array of colors.

After age 1, the monkeys couldn't usually identify colors they had just seen on a computer screen when the on-screen illumination of those colors changed, even after intensive training designed to overcome this problem, Sugita reports in the July 27 Current Biology. In contrast, four macaque monkeys that had been raised in a room illuminated by sunlight and fluorescent lamps recognized colors in a variety of lighting conditions.

Over 3 days of training, all the year-old animals learned to identify matching pairs of black, white, or gray rectangles. After another 3 days of training, the monkeys identified pairs of equally illuminated rectangles with common colors—blue, green, yellow, or red.

After 10 days of training and 3 weeks of further testing, however, those monkeys raised under restricted-illumination conditions still had great difficulty recognizing different shades of the same color as well as identifying the same color illuminated to varying degrees. These problems remained 9 months after the monkeys had been moved to a room illuminated by sunlight and fluorescent lamps.http://louis-j-sheehan.net

"These results indicate that early visual experience is indispensable for normal color perception," Sugita says.

His report is the first clear demonstration that animals can perceive colors, which indicates working cone cells in the retina, but that they lack the capacity for color constancy, comments Stanford University vision researcher Brian A. Wandell. This implies that the brain, not the retina, assumes substantial responsibility for performing color judgments under different lighting conditions, in his view.

Brain-imaging studies are needed to pinpoint disrupted parts of the brain's visual system in monkeys without color constancy, Wandell says.

novel

By the time babies are 6 months old, they distinguish the faces of different people—and can also discern the faces of specific monkeys. Now, researchers have found that with parental coaching, infants can retain their skill at telling animals apart instead of losing it by 9 months of age as babies usually do.Louis J. Sheehan

In their investigations of baby perception, psychologist Olivier Pascalis of the University of Sheffield in England and his team hypothesize that infants rapidly transform themselves from perceptual generalists to specialists (SN: 5/18/02, p. 307: http://www.sciencenews.org/20020518/fob1.asp). Intense practice at discerning different human faces prompts the loss of perceptual insights into nonhuman faces by 9 months of age, the scientists propose.http://ljsheehan.livejournal.com

That perceptual trade-off may not be inevitable, however. From age 6 months to 9 months, babies whose parents show them photographs of monkeys' faces for brief periods hang on to the ability to tell one furry primate's mug from another, Pascalis and his coworkers report in an upcoming Proceedings of the National Academy of Sciences. The researchers are now testing how long this retention lasts.

"Our data further elucidate the role of early experience in the development of face processing," Pascalis says.

In the new study, 26 infants participated in face-recognition trials. While being held by their mothers, the 6-month-olds viewed an image of a monkey's face and then saw that picture presented alongside another monkey's face. All the animals displayed neutral expressions.

Babies looked substantially longer at the novel face in each pair, a sign the researchers take for both recognition of and preference for new faces.http://ljsheehan.livejournal.com

The researchers then gave half of the mothers mug shots of six monkeys, each labeled with a name. For the next week, each mother showed her baby the photos and talked about each monkey for 10 to 20 seconds daily. Photo presentations over the next 3 months tapered off to one per week.

At age 9 months, infants who had been shown monkey faces at home still looked longer at novel monkey faces than they did at faces they had just seen. The 13 babies who received no face training at home looked equally long at novel and previously viewed monkey faces.

The results indicate that babies need only exposure to still images of monkey faces to maintain perceptual sensitivity to them, remarks psychologist Paul C. Quinn of the University of Delaware in Newark, who has collaborated with Pascalis in other work.

The social nature of home practice sessions probably played a big role in preserving infants' ability to distinguish monkey faces, Pascalis adds. Mothers guided their babies' attention and motivated the youngsters to examine the photos, he says.

The findings parallel evidence that babies start out skilled at discerning the sounds of many languages but lose that generic capacity as they learn their parents' language, says Pascalis.

memories

World War II ended 60 years ago, but memories of that conflagration show surprising staying power। Danes who lived through the Nazi occupation, which began in 1940, and the liberation in 1945 remember information associated with those two events with considerable accuracy, a new study finds. Louis J. Sheehan

Vivid recollections of one's surroundings and other personal experiences at the time of momentous, surprising events have been dubbed flashbulb memories. Earlier studies indicated that the accuracy of this type of recall declines substantially for 3 years after such events take place. That led some researchers to posit that after a decade or more, such memories become totally untrustworthy.

However, a healthy proportion of flashbulb memories related to World War II have stayed intact for more than half a century in Danes, say Dorthe Berntsen and Dorthe K. Thomsen, psychologists at the University of Aarhus in Denmark.

Their conclusion hinges on study participants remembering verifiable information related to the wartime events, such as the time of day that the radio announced liberation. Berntsen and Thomsen argue that the accuracy of verifiable information serves as a gauge of the veracity of personal recollections. Their technique conservatively estimates flashbulb-memory accuracy, the researchers contend, since people remember material better if they recount past events spontaneously rather than respond to questions about those events, as in the study.http://louis-j-sheehan.biz

Berntsen and Thomsen administered questionnaires to 145 Danes, ages 72 to 89. None had been diagnosed with a brain disease. Another 65 Danes born during or after World War II, ages 20 to 60, also completed questionnaires.

All the volunteers answered such questions as what the weather was like on occupation and liberation days and whether those days fell on workdays or the weekend.

Elderly participants also reported what they were doing when they heard news of the occupation and liberation, and their most negative and most positive personal memories from World War II.

Older Danes answered far more factual questions correctly than their younger counterparts did, the scientists report in the May Journal of Experimental Psychology: General. For instance, 100 war survivors, compared with only 3 of the younger participants, accurately described weather conditions on the day the Germans invaded Denmark.http://louis-j-sheehan.biz

Nearly all the older Danes cited personal memories related to the two war events. About 80 percent related either a most-negative or a most-positive wartime memory. Participants remember the liberation more clearly and with more details than they recall the invasion.

Individuals who reported having intense emotions at the time of occupation and liberation and who had regularly thought about those events after the war revealed the most detailed personal memories.http://louis-j-sheehan.biz

The 66 participants who reported ties to the Danish resistance movement displayed particularly accurate factual recall and remembered personal experiences with great clarity.

"Occupation and liberation during World War II dramatically affected everyone in Denmark," comments psychologist David C. Rubin of Duke University in Durham, N.C. "Danes now at advanced ages appear to have pretty accurate flashbulb memories for those events."

Liberation loomed large in the older Danes' memories because it's often publicly commemorated in Denmark, the investigators say.

cassini

Swooping within 49 kilometers of Saturn’s tiny, geologically active moon Enceladus, the Cassini spacecraft has pinpointed the locations of the icy geysers that erupt from the southern hemisphere of this wrinkled moon’s surface.http://Louis2J2Sheehan2Esquire.US

Images taken by Cassini during an Aug. 11 flyby have revealed new details about the south polar fractures, dubbed tiger stripes, from which the geysers emanate. The images reveal that the fractures are about 300 meters deep and have V-shaped inner walls. Some fractures are flanked by large deposits of fine material, another indication that those trenches are the geysers’ source. Blocks of ice, house-sized and larger, litter the surrounding, more finely fractured terrain.

ENLARGE | Cassini shot past the surface of Saturn's moon Enceladus on August 11, recording seven high-resolution images that home in on warm regions within the moon's tiger-stripe fractures, also known as sulci. This composite image shows two of the stripes; circles indicate the location of geysers that emanate from these fractures.NASA/JPL/Space Science Institute

The geysers blast icy particles, water vapor and trace amounts of organic compounds into space, and researchers are hoping to use the images and other Cassini data to determine whether these vents originate from a subsurface ocean. The craft’s recent detection of sodium in Saturn’s icy E ring, whose ice particles are supplied by Enceladus, suggests that the moon has an underground reservoir of salty water.

Icy particles line some of the fractures, even the regions between geysers. One explanation is that when warm vapor from an underground source rises to the cold surface, ice particles condense and settle on the ground, sealing off a vent. New jets may then erupt from other locations along the same fracture.

ENLARGE | This close-up of an Enceladus tiger-stripe fracture known as Damascus Sulcus shows the location of two geysers (yellow circles).NASA/JPL/Space Science Institute

“At the limited spatial resolution on the tiger stripes that we had from previous flybys, we could not previously identify any unique morphological [shape], albedo [reflectivity] or color details that would allow us to distinguish the active vent locations from the rest of their tiger stripes,” notes Cassini researcher Paul Helfenstein of Cornell University.http://Louis2J2Sheehan2Esquire.US

The Aug. 11 passage was Cassini’s fifth close flyby of Enceladus and the nearest yet to the moon’s surface. From Cassini’s point of view, Enceladus streaked past at a relative speed of 64,000 kilometers per hour, making it extremely challenging to take sharp, smear-free images.

Helfenstein devised a strategy of pointing the craft far ahead of Enceladus and then turning the craft as quickly as possible in the direction of the moon’s path. That enabled the craft to take seven high-resolution images of the tiger stripes in rapid सुक्सस्सिओं.

Cassini will next pass by Enceladus on October 10, when the craft should venture even closer, within 25 kilometers of the moon’s surface. Five other flybys are plannedcassini

Pakefield

लुईस जे। शीहन Scientists excavating ancient river sediment along England's southeastern coast have unearthed stone tools from roughly 700,000 years ago, the earliest evidence of human ancestors in northern Europe।

A team led by Simon A. Parfitt of University College London found 32 pieces of worked flint, including a cutting implement with a sharpened edge and a fist-size rock from which smaller, tool-size pieces had been hammered. These unexpected discoveries occurred near the village of Pakefield, Suffolk, and near the base of an eroding cliff that has been combed by fossil hunters for the past 200 years.

Fossils of extinct animals found near the artifacts, as well as measurements of Earth's magnetic field within the sediment, guided the scientists' age estimate. Remnants of cold-averse animals, insects, and plants in the tool-bearing deposit further indicate that a warm, Mediterranean climate prevailed there 700,000 years ago, the researchers report in the Dec. 15, 2005 Nature. At that time, a land bridge connected England to northwestern Europe.

The Pakefield finds show that human ancestors reached northern and southern parts of Europe at around the same time, remarks John McNabb of the University of Southampton in England. Other researchers previously uncovered remains of Homo species that inhabited Mediterranean areas, such as Spain and Italy, by at least 800,000 years ago। Until now, the earliest evidence of human ancestors in England dated to about 500,000 years ago. http://louis-j-sheehan.biz

Faced with a climate that fluctuated dramatically every few thousand years, our evolutionary forerunners probably spread northward during warm times and retreated south during cold phases, says University College's Anthony J। Stuart, a coauthor of the new study.

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