Some people are still being told that 200:1 is all we can see.... - Page 17 - AVS Forum
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post #481 of 505 Old 01-14-2007, 07:19 AM
 
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Originally Posted by ChrisWiggles View Post

The only scientific statements that directly bear on the questions at hand come from the folks at Brightside. And they cite 100,000:1 as the instantaneous CR capability of the human eye across a single scene with no iris adjustment.

Chris are the 'folks' at Brightside ignorant? The scientific evidence referenced in this very thread, proves beyond any doubt that 100,000:1 is ridiculous!

http://proav.pubdyn.com/Tech_Apps/Ma...rallaxView.htm
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Originally Posted by PeterPutman View Post

My preferred settings resulted in brightness readings of 350+ lumens with average contrast at 275:1 and peak contrast close to 400:1. In a darkened room, your eye would be hard-pressed to see the difference between 400:1 and 500:1, both of which far exceed the eye's instantaneous (non-irised) contrast ratio.

You can reach him at pete@hdtvexpert.com. Darin
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I am truly blessed with an incredible talent and ability

Please provide a reference for the Brightside info (Thanks in advance). Anyone who made such a statement does not comprehend the complex mechanisms of the HVS, including the obvious contribution/function of the eyes Iris
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post #482 of 505 Old 01-14-2007, 10:36 AM
 
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The scientific evidence referenced in this very thread, proves beyond any doubt that 100,000:1 is ridiculous!

The has been no scientific reference that says anything of the sort. No, indeed it is you who has displayed astounding ignorance.
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post #483 of 505 Old 01-14-2007, 11:13 AM
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Darin: If I understand you correctly, you don't care whether or not you can different levels. So let's hypotheitically create a high CR scene that is projected with say 300:1 and 30,000:1. How many levels of brightness do you think you can resolve under both conditions? The squares test tells me that on my monitor I cannot resolve it from display black. I don't need the 30,000:1 display to create that effect and before Chris kicks in with a display problem, the square is nicely rendered. Are you saying that the 30,000:1 display will help me see that square? Frankly, I don't have the full answer to that. I would assume that the high CR display would extend both black and white levels. So maybe I could actually distinguish the 2% square against the background. But what about 0.5% brightness squares? Or 0.05% squares? It's not really easy to come up with these values and therefore I would love to see some publication that addresses this issue under defined experimental conditions.

It is even more difficult to compare displays, because brightness certainly plays a role. A display with twice the brightness will generate an image that looks more contrasty than a dimmer display even if they were capable of creating the same CR.
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post #484 of 505 Old 01-14-2007, 12:41 PM
 
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The question of what's the maximum CR is very different from what's the minimum luminance difference we can see. I've said this many many times, it's consistent confusion of JND issues with maximum CR issues.
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post #485 of 505 Old 01-14-2007, 12:49 PM - Thread Starter
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Originally Posted by armadillo View Post

Gary: It wasn't me who took the mouse pointer extreme. I'm asking you whether you would see intensity differences in the small bright spot and I'm saying, you won't, because the photoreceptors that are hit by the bright spot are saturated.

You're still looking at the smallest difference (between 100% and 99%), not the largest, and are you now limiting 'what we can see' to just a few saturated receptors rather than the fovea or the eye in it's entirety? That seems quite a limitation in order to make the 200:1 number work. If you want a darker portion within the pointer that may be tricky since the pointer is already very small, and I would think the limitation could then be due to the contrast 'at a boundary' effect or the limitation of the smallest range of CR we can see. It won't stop me seeing the larger contrast numbers I quoted before though.

The squares test is like taking a vision test while looking at the sun or having a torch shone in your eye, and there will always be limitations with that.

We don't look at an image with just the fovea, we use the entire eye, so the capabilities of the entire eye are what we should be stating, not individual parts IMHO. It's not how we see images in real life, and tunnel vision is considered a disability.

Of course I agree with the elevator phenomenon, but I think it it's more an iris function than a chemical function, but either way, the height of my elevator appears to be over 1000:1

Gary

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post #486 of 505 Old 01-14-2007, 12:52 PM
 
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either way, the height of my elevator appears to be over 1000:1

Wow, I'm glad to see there's another person with extraordinary visual capabilities! Are you also capable of functioning at night? That's great! Well, at least there's two of us on earth who can go outside at night. Too bad everyone else can't.
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post #487 of 505 Old 01-14-2007, 12:54 PM
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Quote:
Originally Posted by Gary Lightfoot View Post

The squares test is like taking a vision test while looking at the sun or having a torch shone in your eye, and there will always be limitations with that.

So 2% brightness vs 100% brightness is like the sun? The 2% square simply vanishes on 700:1 (nominal) display. You ought to get out more to see the sunlight
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post #488 of 505 Old 01-14-2007, 01:34 PM - Thread Starter
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There's a relationship between light intensity and iris function. The greater the intensity, the more the iris will function to limit it. I can see over 1000:1 in the image I have posted, but if you shine a bright light in my eye, the iris will close down raising the 'elevator' and reducing the visibility of much of the surround image. I will also be subject to the limitation of veiling glare and boundary effects to limit what I can see outside of the bright light.

Are you saying that having a bright light like a torch shone in your eye will not reduce your lower light vision capabilities?

Gary

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Originally Posted by elmalloc
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post #489 of 505 Old 01-14-2007, 02:54 PM
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Quote:
Originally Posted by Gary Lightfoot View Post

There's a relationship between light intensity and iris function. The greater the intensity, the more the iris will function to limit it. I can see over 1000:1 in the image I have posted

There are 2 issues I see with your experiments as you have posted:

1) they involve motion; you move a mouse pointer, or move your hand for a shadow puppet, you will immediately get luminance adaptation, which can occur in < 100 ms, without any iris adaptation!
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Originally Posted by Heinrich and Bach View Post

Whereas the usable light intensity in our visual world varies by approximately eight orders of magnitude, the range over which we discriminate differences in light intensity varies only approximately 100-fold. Photochemical and neural mechanisms keep the limited range of discriminability in the range of the prevailing luminance, known as luminance adaptation. Similarly, although on a smaller scale, contrast adaptation shifts the steep part of the contrast transfer function to match the prevailing contrast condition

http://www.iovs.org/cgi/content/full/42/11/2721
2) Your experiments are not double blind. A lot of times we "see" what we expect to see
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post #490 of 505 Old 01-14-2007, 02:59 PM - Thread Starter
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The image was paused, and the mouse motionless. It needed to be like that to get readings. With the image like that, no iris adaption was happening

Gary

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Originally Posted by elmalloc
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post #491 of 505 Old 01-14-2007, 03:15 PM
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Originally Posted by Gary Lightfoot View Post

With the image like that, no iris adaption was happening

We can remove iris adaptation, which takes seconds to minutes from these discussions. You will still get luminance adaptation, in 2 to 100 ms if there is a change in the precept (visual frame).
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post #492 of 505 Old 01-14-2007, 03:39 PM - Thread Starter
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The image was static whilst I was looking at it to see if I could still see all the detail, so whatever adaption was happening had happened (all bright and dark elements were within very close proximity). Even so, if 2 to 100ms adaption was taking place, that's pretty much instantaneous then. If we can't use millisecond adaption to clarify 'what we can see' then we may as well ignore our eyes all together then, since we're all using them illegally according to the 200:1 gang

Gary

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Originally Posted by elmalloc
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post #493 of 505 Old 01-14-2007, 04:09 PM
 
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Originally Posted by HoustonHoyaFan View Post

We can remove iris adaptation, which takes seconds to minutes from these discussions. You will still get luminance adaptation, in 2 to 100 ms if there is a change in the precept (visual frame).

Here we go again, you're imposing limitations. We're interested in the MAXIMUM, not some other limited example where in that particular situation things may be less than the maximum. As I exaggerated before, most people are capable are moving their eyes around. We don't have them glued in our head and we're not strapped down to a gurney. When you view a single scene, you can move your eyes around.
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post #494 of 505 Old 01-14-2007, 06:52 PM
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Originally Posted by Gary Lightfoot View Post

Even so, if 2 to 100ms adaption was taking place, that's pretty much instantaneous then. If we can't use millisecond adaption to clarify 'what we can see'

I suspect that we could come to some reasonable approximation of a top end CR number for video displays if we could start from some established scientific baseline. We seem unable as a group to even do that.

I suggest we start with 2 common "facts" in the HVS community:

1) The retinal ganglion cells can output a luminance range of <200:1 per precept (visual frame). The CW in HVS research is ~100:1.

2) Luminance adaption (contrast gain) can occur in as little as ~1/10 sec.

If we put those numbers together with the video frame rate of 1/60 sec maybe some like Darin can come up with a number that most of us thinks makes sense.
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post #495 of 505 Old 01-14-2007, 07:00 PM
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Originally Posted by HoustonHoyaFan View Post

2) Luminance adaption (contrast gain) can occur in as little as ~1/10 sec.

Although that depends on the average light level. For dark scenes it takes tens of seconds to minutes. So a short strobe of light will rest the HVS.
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post #496 of 505 Old 01-14-2007, 07:50 PM
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How did the topic of this thread get turned into a discussion about the condition where the eye is capable of seeing a "MAXIMUM CR" ONLY?

Seems to me it is more informative to discuss all the variable parameters that limit CR range.

Obviously, there could be a difference in seeing high CR dark detail in a scene, if the bright area is 3" in diameter and 3' in diameter.

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post #497 of 505 Old 01-14-2007, 08:09 PM
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Glen: I think that Darin and Chris have come to realize that they cannot win the simultaneous contrast argument. Far too many references and answers from scientists do indeed state that simultaneous contrast is limited to 100-300:1. So now they are shifting to spatial and temporal contrast aspects which were never in dispute. So I think I'll abandon this thread, since I know what I need to know. If Chris wants to move into face-saving post mode, fine with me. I never had any hopes to convince him anyway.
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post #498 of 505 Old 01-15-2007, 09:20 AM
 
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Originally Posted by HoustonHoyaFan View Post

We can remove iris adaptation, which takes seconds to minutes from these discussions. You will still get luminance adaptation, in 2 to 100 ms if there is a change in the precept (visual frame).

I think you have this backwards..i.e. persistence of vision would illustrate local luminance adaption is relatively slow

http://www.handprint.com/HP/WCL/color1.html
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The aperture into the eye or pupil is fringed by a light sensitive iris, spread over the front of the lens, which acts as a diaphragm to adjust the pupil from a minimum diameter of 2mm up to a maximum of 8mm (in young adults). This produces a change in pupil area from about 3.5 mm2 to 20 to 35 mm2, which provides an 87% to 95% reduction in the amount of light entering the eye. However, this represents a tiny fraction of the total range of illmination the eye can handle. Additional changes in luminance adaptation occur in the retina and brain across a span of several minutes; the iris makes prompt, momentary adjustments to changes in light intensity within the same light environment.

http://micro.magnet.fsu.edu/primer/l...sionintro.html
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Adaptation of the eye enables vision to function under such extremes of brightness. However, during the interval of time before adaptation occurs, individuals can sense a range of brightness covering only about three decades. Several mechanisms are responsible for the ability of the eye to adapt to a high range of brightness levels. Adaptation can occur in seconds (by initial pupillary reaction) or may take several minutes (for dark adaptation), depending upon the level of brightness change. Full cone sensitivity is reached in about 5 minutes, whereas it requires about 30 minutes to adapt from moderate photopic sensitivity to the full scoptic sensitivity produced by the rod cells

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post #499 of 505 Old 01-15-2007, 09:50 AM
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Originally Posted by tbrunet View Post

I think you have this backwards..i.e. persistence of vision would illustrate local luminance adaption is relatively slow

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Originally Posted by armadillo View Post

Although that depends on the average light level. For dark scenes it takes tens of seconds to minutes. So a short strobe of light will rest the HVS.

There are two types of luminance adaptation mechanisms; contrast adaptation which takes seconds to minuter, and contrast gain which can take < 100 ms.
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Originally Posted by Thomas Stephan Heinrich and Michael Bach View Post

Whereas the usable light intensity in our visual world varies by approximately eight orders of magnitude, the range over which we discriminate differences in light intensity varies only approximately 100-fold. Photochemical and neural mechanisms keep the limited range of discriminability in the range of the prevailing luminance, known as luminance adaptation. Similarly, although on a smaller scale, contrast adaptation shifts the steep part of the contrast transfer function to match the prevailing contrast condition.1 On a single-cell basis, there is a distinction between contrast adaptation and contrast gain control. The latter represents rapid changes, taking approximately 100 msec, as found in retinal ganglion cells of cats2 and MX ganglion cells of macaques.3 Conte et al.4 also found rapid changes in humans by means of pattern electroretinogram (PERG) and visual evoked potentials (VEPs). Contrast adaptation refers to relatively long-term changes (seconds to minutes).5 6

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post #500 of 505 Old 01-15-2007, 10:36 AM
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Quote:
Originally Posted by HoustonHoyaFan View Post

I suspect that we could come to some reasonable approximation of a top end CR number for video displays if we could start from some established scientific baseline. We seem unable as a group to even do that.

I suggest we start with 2 common "facts" in the HVS community:

1) The retinal ganglion cells can output a luminance range of <200:1 per precept (visual frame). The CW in HVS research is ~100:1.

2) Luminance adaption (contrast gain) can occur in as little as ~1/10 sec.

If we put those numbers together with the video frame rate of 1/60 sec maybe some like Darin can come up with a number that most of us thinks makes sense.

One thing I am not clear about is whether you consider something being shown at 60 frames per second to be 60 simultaneous frames with each limited to 200:1 without eye movement, or if just the motion in the images themselves negates the thing about simultaneous frames. For instance, the HVS is using motion as one of the clues to make out detail. As an example, if one frame had 250:1 and things outside 200:1 were crushed and the next frame had the exact same levels, except with the brightest and darkest parts shifted laterally, is it your claim that a person would not be able to perceive that motion at both ends. Again, in this case both images have the same CR with the same peak and the same valley, but just in different spots.

It also isn't clear to me if your position is that the ganglion cells could not report anything different for a 200:1 image than if it was changed to 20k:1 by lowering the darkest item. I don't see anything that indicates that the ganglion cells couldn't report something smaller than is coming off the screen. For example, output 100:1 even though the image is 200:1, but would report 200:1 if the image were 20k:1. Do you see anything that makes that clear? If there is 4% washout from a bright object to the darker part of the image, then it sure looks like they could report less than is coming off the screen and still have room to report a higher number if the CR coming off the screen increased significantly.
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Originally Posted by GlenC View Post

How did the topic of this thread get turned into a discussion about the condition where the eye is capable of seeing a "MAXIMUM CR" ONLY?

Seems to me it is more informative to discuss all the variable parameters that limit CR range.

Obviously, there could be a difference in seeing high CR dark detail in a scene, if the bright area is 3" in diameter and 3' in diameter.

While it is interesting to consider different cases where we are more limited and less limited, this thread was about the upper limit at once or in one image. If a person says that people can't see anything beyond x:1 and it turns out we can under some conditions (but that there are also conditions where we can't) then they are wrong if they don't specify any conditions and make it out that it is for all conditions. And if they are teaching ISF courses and making people think that images don't need any more than 200:1 (or 300:1 or whatever it is) at once because we couldn't see improvements beyond that, then that is unfortunate.

Again, if a person wants to say that under y conditions we can't see beyond x:1, then that is fine (if it is true). But a test that uses images that limit our vision more than other images do doesn't prove an upper limit and the result should not be claimed as an upper limit. I bet I could come up with images where you couldn't tell the difference between 20:1 and 20k:1, but I wouldn't claim 20:1 as the limit.

--Darin

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post #501 of 505 Old 01-15-2007, 11:22 AM
 
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Quote:
Originally Posted by GlenC View Post

How did the topic of this thread get turned into a discussion about the condition where the eye is capable of seeing a "MAXIMUM CR" ONLY?

Seems to me it is more informative to discuss all the variable parameters that limit CR range.

Obviously, there could be a difference in seeing high CR dark detail in a scene, if the bright area is 3" in diameter and 3' in diameter.

Uh... since the first post...?
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post #502 of 505 Old 01-15-2007, 11:27 AM
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Darin, my intrepretation of the 200:1 statement is related to the overall bright image with dark detail. I have not been able to test a ANSI CR test pattern to determine if with increased brightness (luminance) we have a change in visible CR and it's threshold.

I believe this leads to >>> In a totally light controlled, dedicated theater, you don't need 60+fL off the screen, you want better blacks. It would take too long for the eye to adjust to a dark scene after seeing very bright scenes.

Unfortunately, the statement made here about the comment in the ISF class is not a complete statement, it lacks meaning. We can only assume what the missing pieces are. There has been some agreement in this thread that "in certain situations" the eye may be limited to 200:1. That alone validates the statement, under those conditions. On the other-hand, Chris's comment that we can see more than 1000:1 is valid for his defined conditions, but is not valid for "all" conditions.

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post #503 of 505 Old 01-15-2007, 12:40 PM
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Quote:
Originally Posted by GlenC View Post

Unfortunately, the statement made here about the comment in the ISF class is not a complete statement, it lacks meaning. We can only assume what the missing pieces are.

As I mentioned before, I have discussed this with somebody who told me he teaches ISF courses. We talked about what image he has used and it was clear to me that he didn't understand that way more than that is needed for simultaneous CR before we couldn't see improvement in simultaneous CR off the screen. That is, before we started talking. After we talked hopefully he understood it more (he seemed to) and went off and did some of the testing I suggested. It would have been much easier to discuss this with a projector in a dark room and some examples, but we live in different states.
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Originally Posted by GlenC View Post

There has been some agreement in this thread that "in certain situations" the eye may be limited to 200:1. That alone validates the statement, under those conditions.

Then only for those conditions. Do you agree that "in certain situations" the eye may be limited to 20:1? I could say that validated statements that we are limited to 20:1, under those conditions, but then I should have said it was for those conditions and not just said that humans are limited to 20:1.

I believe this thread started out asking about the upper limit. That is, an "up to" condition. Not that we can see that under every condition, as we are more limited in some cases than others.

--Darin

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post #504 of 505 Old 01-16-2007, 05:11 AM
 
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Quote:
Originally Posted by GlenC View Post

I believe this leads to >>> In a totally light controlled, dedicated theater, you don't need 60+fL off the screen, you want better blacks. It would take too long for the eye to adjust to a dark scene after seeing very bright scenes.

Glen it's as simple as that..look at a bright scene, your dark adaptation is reset. In fact the afterimage is sill there if you close your eyes. How is one going to appreciate that superior black level if you can't perceive it? The link below illustrates this very limitation!

Quote:


Afterimage: Prolonged stimulation by a bright object desensitizes part of the retina. This area appears as a negative afterimage, a dark area or complimentary color that matches the original shape. The afterimage may remain for 30 seconds or longer.
http://xsrv.mm.cs.sunysb.edu/334/per...perception.htm

Stare at the black dot in the center of the image above. When the image changes, you should see a yellow afterimage in the negative (white) space.

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Dark adaptation
Two phases of recovery: cones fast, rods slow: why?
Bleaching of visual pigment: cones regenerate fast, rods slow
But sensitivity decreases 100 fold for a 10% bleach! Why?

What is the structure that adapts?
Independence of left and right eyes
Rod-cone independence (approximate) means adaptation precedes the retinal ganglion cell (the common path for rod and cone signals)
BUT: in rod vision, adaptation is in a pool (Rushton): bleaching one rod reduces the effectiveness of stimuli for nearby rods. The rods themselves do not adapt, but they send a signal to a later neural pool to provoke sensitivity adjustments there.
Cone vision: no pool, each cone has its own sensitivity control.
Why this makes sense: few photons per rod, many per cone
Evidence for the signal from bleached photoreceptors: pupil constricted in the dark; afterimage; both effects are due to a signal that originates in the retina (pressure blinding).
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