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In a remarkable experiment, researchers found that a man who was rendered completely blind by several strokes could deftly navigate an obstacle course unaided, easily avoiding boxes and sidling around pieces of office equipment. The patient, known only as TN, was left blind after damage to the visual (striate) cortex in both hemispheres of the brain following consecutive strokes. His eyes are normal but his brain cannot process the information they send in, rendering him totally blind [BBC News]. Researchers say TN’s successful performance was an example of the phenomenon “blindsight,” and say it suggests that some small amount of information is being transmitted from his undamaged eyes to a more primitive part of his brain, which operates beneath the level of consciousness.

TN usually walks with a cane, but researcher Beatrice de Gelder convinced him to put it aside and to try to navigate the obstacle course without its help. He was able to do so flawlessly, despite being unable to consciously see any of the obstacles. Head down and hands loose by his side, he twisted his body to slalom slowly but surely between a camera tripod and a swingbin, and neatly stepped around a random series of smaller items. “At first he was nervous,” says de Gelder. “He said he wouldn’t be able to do it because he was blind.” The scientists broke into spontaneous cheers when he succeeded [Nature News].

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Researchers have determined the mechanism by which the world’s simplest vision system works. A team of biologists spent a decade studying the larvae of the marine rag-worm Platynereis, a tiny creature with just two cells that respond to light and direct the worm to swim towards it. The rag-worm and other zooplankton like krill drift in the ocean’s water columns, swimming up from the depths towards the light in order to graze on marine plants called phytoplankton near the surface. This movement, called phototaxis, is the biggest biomass displacement in the world [AFP].

The rag-worm has two cells that work together as “proto-eyes”: one pigment cell and one light-sensitive cell. First, the pigment cell absorbs light and casts a shadow over the photoreceptor cell. The shape of the shadow varies according to the position of the light source. The photoreceptor cell then converts this light signal into electricity, sending it in a signal along a nerve that connects to a band of cells endowed with thin hairs, called cilia, that beat to displace water [AFP]. So although the worm sees no images, it can sense the difference between light and dark and swim in the right direction.

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Tennis referees are far more likely to make wrong “out” calls than wrong “in” calls, according to a new study. A quirk of our visual perception system, which helps us anticipate the motion of an object, seems to bias our perception of where a speeding tennis ball stops moving. “This is not a problem with referees,” says study co-author David Whitney…. “It’s a consequence of human visual processing … a visual illusion caused by a mechanism that allows the system to localize a moving object” [Scientific American].

The idea to study this visual illusion in a real-world context came to Whitney during a Wimbledon match as he watched a player challenge and overturn a referee’s call. For the study, published in Current Biology [subscription required], the researchers used Hawk-Eye technology, a system of high-speed cameras that is often used for contested calls in tennis matches. Three scientists independently reviewed video and instant replay of 4,457 randomly selected points from the 2007 Wimbledon championships. Of the 83 calls that the video and instant replay showed were wrong, 70 were “out” calls [Scientific American]. Without the visual bias, there should have been the same number of wrong “out” calls as “in” calls.

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