内容摘要：“Before this clinic, we used traditional ways to treat them,” he explained, describing how nails were once crudely removed from the animals’ legs with a knife. He is grateful that his donkeys now have access to professional care for their injuries and infections.

“Before this clinic, we used traditional ways to treat them,” he explained, describing how nails were once crudely removed from the animals’ legs with a knife. He is grateful that his donkeys now have access to professional care for their injuries and infections.

How do humans perceive colour?The human eye perceives colour via three types of photoreceptor or “cone cells” in the retina. S cones pick up shorter, blue wavelengths of light; M cones detect medium, green wavelengths; and L cones detect longer, red wavelengths.

“The signals from these cones are then sent through a complex series of cells in the retina that act to clean up and integrate the signal before passing it down the optic nerve through parts of the brain,” Francis Windram, a research associate at the department of life sciences at Imperial College London, told Al Jazeera.The part of the brain that the visual information is passed to is the visual cortex.How did scientists find the ‘new’ colour?

In normal vision, the function of M cones overlaps with the neighbouring S and L cones, so any light that stimulates M cones also activates the other two cones. The M cones don’t function alone.“There’s no wavelength in the world that can stimulate only the M cone,” Ren Ng, a professor of electrical engineering and computer sciences at UC Berkeley, explained in an article published on its website.

“I began wondering what it would look like if you could just stimulate all the M cone cells. Would it be like the greenest green you’ve ever seen?”

So Ng teamed up with Austin Roorda, one of the creators of the Oz technology and a professor of optometry and vision science at UC Berkeley.Vallejo’s synthetic memory of these meetings is in black and white. The image is vague, almost like someone has taken an eraser to it to blur the details. But it is still possible to make out the scene: a crowd of people gathered in a forest. Some sit, others stand beneath a canopy of trees.

Looking at the image, Vallejo says he felt transported to the clandestine assemblies in the Barcelona woods, where as many as 50 or 60 people would gather in a tense atmosphere.“I found myself truly immersed in the image,” he says.

“It was like entering a kind of time tunnel,” he adds.Vallejo suffered memory loss around the ordeal of his arrests, imprisonment and torture.