Poorly designed backward retina (Introduction)
by David Turell 
, Sunday, December 16, 2012, 17:18 (4361 days ago)
Easy to understand science report on mammalian retinas:-To the atheists, poor design, huh?- http://www.alphagalileo.org/ViewItem.aspx?ItemId=126974&CultureCode=en-Full quote:-"To make information transmission to the brain reliable, the retina first has to "digitize" the image. Until now, it was widely believed that this step takes place in the retinal ganglion cells, the output neurons of the retina. Scientists in the lab of Thomas Euler at the University of Tübingen, the Werner Reichardt Centre for Integrative Neuroscience and the Bernstein Center Tübingen were now able to show that already bipolar cells can generate "digital" signals. At least three types of mouse BC showed clear evidence of fast and stereotypic action potentials, so called "spikes". These results show that the retina is by no means as well understood as is commonly believed. The retina in our eyes is not just a sheet of light sensors that ... like a camera chip ... faithfully transmits patterns of light to the brain. Rather, it performs complex computations, extracting several features from the visual stimuli, e.g., whether the light intensity at a certain place increases or decreases, in which direction a light source moves or whether there is an edge in the image. To transmit this information reliably across the optic nerve - acting as a kind of a cable - to the brain, the retina reformats it into a succession of stereotypic action potentials ... it "digitizes" it. Classical textbook knowledge holds that this digital code ... similar to the one employed by computers ... is applied only in the retina's ganglion cells, which send the information to the brain. Almost all other cells in the retina were believed to employ graded, analogue signals. But the Tübingen scientists could now show that, in mammals, already the bipolar cells, which are situated right after the photoreceptors within the retinal network, are able to work in a "digital mode" as well. Using a new experimental technique, Tom Baden and colleagues recorded signals in the synaptic terminals of bipolar cells in the mouse retina. Based on the responses of these cells to simple light stimuli, they were able to separate the neurons into eight different response types. These types closely resembled those expected from physiological and anatomical studies. But surprisingly, the responses of the fastest cell types looked quite different than expected: they were fast, stereotypic and occurred in an all-or-nothing instead of a graded fashion. All these are typical features of action potentials. Such "digital" signals had occasionally been observed in bipolar cells before, but these were believed to be rare exceptional cases. Studies from the past two years on the fish retina had already cast doubt on the long-held belief that BCs do not spike. The new data from Tübingen clearly show that these "digital" signals are systematically generated in certain types of mammalian bipolar cells. Action potentials allow for much faster and temporally more precise signal transmission than graded potentials, thus offering advantages in certain situations."
Poorly designed backward retina
by David Turell , Saturday, July 26, 2014, 15:43 (3774 days ago) @ David Turell
More evidence on how wonderously the retina is designed to conduct photons:-http://phys.org/news/2014-07-fiber-optic-pipes-retina-simple.html
Poorly designed backward retina
by David Turell , Thursday, October 09, 2014, 14:56 (3699 days ago) @ David Turell
Another article explaining how beautifully it works. Calls it counterintuitive!-http://www.the-scientist.com//?articles.view/articleNo/40996/title/Guiding-Light/
Poorly designed backward retina: complex night vision change
by David Turell , Thursday, September 13, 2018, 18:32 (2264 days ago) @ David Turell
There are complex alterations for night vision:
https://medicalxpress.com/news/2018-09-eyes-natural-version-night-vision.html
"To see under starlight and moonlight, the retina of the eye changes both the software and hardware of its light-sensing cells to create a kind of night vision. Retinal circuits that were thought to be unchanging and programmed for specific tasks are adaptable to different light conditions, say the Duke scientists who identified how the retina reprograms itself for low light.
"'To see under starlight, biology has had to reach the limit of seeing an elementary particle from the universe, a single photon," said Greg Field, an assistant professor of neurobiology and biomedical engineering at Duke University. "It's remarkable at night how few photons there are."
***
"Even in the best lighting, identifying the presence and direction of a moving object is key to survival for most animals. But detecting motion with a single point of reference doesn't work very well. So, the retinas of vertebrates have four kinds of motion-sensitive cells, each specifically responsive to a motion that is up, down, right or left.
"When an object is moving in precisely one of those directions, that population of neurons will fire strongly, Field said. However, if the motion is halfway between up and left, both populations of cells will fire, but not quite as strongly. The brain interprets that kind of signal as motion going both up and left.
"'For complex tasks, the brain uses large populations of neurons, because there's only so much a single neuron can accomplish," Field said.
***
"In a study with mouse retinas conducted under a microscope equipped with night vision eye pieces in a very dark room, graduate student Xiaoyang Yao in Field's lab found that the retinal cells sensitive to upward movement change their behavior in low light. The "up" neurons will fire upon detecting any kind of movement, not just upward.
"A small sample of mouse retina was placed on an electrode array that can measure the individual firing of hundreds of neurons at once "and then we show it movies," Field said. "Xiaoyang's insight was to go and look at what these cells do in day and night," Field said. "She noticed a difference and wondered why."
"When there is much less light available, a weak signal of motion from the 'up' neurons, coupled with a weak signal from any of the other directional cells can help the brain sense movement, similar to the way it interprets two directional signals as being a motion that is something in between.
***
"What's important for now is that the eye and brain alter their computation of motion in low-light. "We've learned that large populations of retinal neurons can adapt their function to compensate for different conditions," Field said.
"The retina consists of many circuits working in parallel, said Jeffrey Diamond, a senior investigator at the National Institute of Neurological Disorders and Stroke who also studies visual processing in the retina. "We're learning that these circuits are doing different things at different times of day," said Diamond, who was not involved with Field's paper."
Comment: So the 'poorly designed' retina can adapt to any level of light! This cannot have happened by chance mutations.
Poorly designed backward retina: complex night vision change
by Balance_Maintained , U.S.A., Thursday, September 13, 2018, 20:33 (2264 days ago) @ David Turell
There are complex alterations for night vision:
https://medicalxpress.com/news/2018-09-eyes-natural-version-night-vision.html
"To see under starlight and moonlight, the retina of the eye changes both the software and hardware of its light-sensing cells to create a kind of night vision. Retinal circuits that were thought to be unchanging and programmed for specific tasks are adaptable to different light conditions, say the Duke scientists who identified how the retina reprograms itself for low light.
"'To see under starlight, biology has had to reach the limit of seeing an elementary particle from the universe, a single photon," said Greg Field, an assistant professor of neurobiology and biomedical engineering at Duke University. "It's remarkable at night how few photons there are."
***
"Even in the best lighting, identifying the presence and direction of a moving object is key to survival for most animals. But detecting motion with a single point of reference doesn't work very well. So, the retinas of vertebrates have four kinds of motion-sensitive cells, each specifically responsive to a motion that is up, down, right or left.
"When an object is moving in precisely one of those directions, that population of neurons will fire strongly, Field said. However, if the motion is halfway between up and left, both populations of cells will fire, but not quite as strongly. The brain interprets that kind of signal as motion going both up and left.
"'For complex tasks, the brain uses large populations of neurons, because there's only so much a single neuron can accomplish," Field said.
***
"In a study with mouse retinas conducted under a microscope equipped with night vision eye pieces in a very dark room, graduate student Xiaoyang Yao in Field's lab found that the retinal cells sensitive to upward movement change their behavior in low light. The "up" neurons will fire upon detecting any kind of movement, not just upward.
"A small sample of mouse retina was placed on an electrode array that can measure the individual firing of hundreds of neurons at once "and then we show it movies," Field said. "Xiaoyang's insight was to go and look at what these cells do in day and night," Field said. "She noticed a difference and wondered why."
"When there is much less light available, a weak signal of motion from the 'up' neurons, coupled with a weak signal from any of the other directional cells can help the brain sense movement, similar to the way it interprets two directional signals as being a motion that is something in between.
***
"What's important for now is that the eye and brain alter their computation of motion in low-light. "We've learned that large populations of retinal neurons can adapt their function to compensate for different conditions," Field said.
"The retina consists of many circuits working in parallel, said Jeffrey Diamond, a senior investigator at the National Institute of Neurological Disorders and Stroke who also studies visual processing in the retina. "We're learning that these circuits are doing different things at different times of day," said Diamond, who was not involved with Field's paper."
Comment: So the 'poorly designed' retina can adapt to any level of light! This cannot have happened by chance mutations.
Bet they didn't see that one coming.
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What is the purpose of living? How about, 'to reduce needless suffering. It seems to me to be a worthy purpose.