One issue with the idea of neurons firing or not depending on what color you see, this isn't correct. The neurons are firing all the time, their rates go up and down depending on the amount of stimulation a given color receptor in the rods receives. This is important because of the overlap in the spectral sensitivities of the receptors and how this information is processed.

I would also remind again that the color visual system far pre-dates language, humans, and probably mammals. Language really shouldn't enter the discussion about the sensation of color. Doing so makes for a lot of confusion, as we keep seeing.

crank wrote:One issue with the idea of neurons firing or not depending on what color you see, this isn't correct. The neurons are firing all the time, their rates go up and down depending on the amount of stimulation a given color receptor in the rods receives. This is important because of the overlap in the spectral sensitivities of the receptors and how this information is processed.

Actually, it is the spike count during a certain period (determined by the retinal circuitry) that determines the apparent light level, not the firing rate per se, which is not determined by the light intensity seen by the photorecpetors involved:
http://www.ncbi.nlm.nih.gov/books/NBK10885/

... One class of amacrine cells, for example, plays an important role in transforming the persistent responses of bipolar cells to light into the brief transient responses exhibited by some types of ganglion cells.

My understanding is that a brighter light level produces a longer pulse train, not a more rapid one. I suspect that the VC uses differing spike rates to distinguish one cone type from another.

I would also remind again that the color visual system far pre-dates language, humans, and probably mammals. Language really shouldn't enter the discussion about the sensation of color. Doing so makes for a lot of confusion, as we keep seeing.

Absolutely! I said as much myself a few days ago, so I assume that remark is addressed to Graham.

EDIT: Also, a class of retinal ganglion cells acts like a kind of unformatted analogue-to-digital converter (ADC) on the photoreceptor output, so that in-line losses in the optic nerve don't degrade the signal too much on its way to the brain.
This is because the photoreceptor output pulses are way too long.

... Also, the timing of photoreceptor pulses is random, and therefore unsuitable for use by the brain. The retinal ganglion cells send digitized, time-integrated photoreceptor signals to the brain, which are more easily handled to generate a visual field than the raw receptor output.

EDIT: The pulse trains do have to stop when the integration of the received light is complete for the given time period (in turn, determined by the retinal circuitry).
(The details are in a very old thread.)

You failed to mention the extreme data reduction already performed in the ganglion cell layers, each layer providing more reduction in bandwidth, or you could say each layer does extensive data processing to extract the important bits, at least important to our visual system. I'm not mentioning a lot here because I don't remember the numbers and don't feel like looking up right now.

What is spike count during a certain period? That's the definition of a rate, pulses/second, a rate. It sounds like you're describing a readout system akin to how CCDs work, the data gets dumped at certain time intervals. That doesn't sound right to me, we would be subject to the same weirdnesses you get when trying to film a TV, unless the data dumping is asynchronous or something? I will have to go look at now, thanks, I really needed more shit to read

crank wrote:...
What is spike count during a certain period? That's the definition of a rate, pulses/second, a rate. It sounds like you're describing a readout system akin to how CCDs work, the data gets dumped at certain time intervals. That doesn't sound right to me, we would be subject to the same weirdnesses you get when trying to film a TV, unless the data dumping is asynchronous or something? I will have to go look at now, thanks, I really needed more shit to read

It may not "sound right" to you, crank. but the only paper on the subject that I ever found indicated that the above process is what happens, and I remember seeing the time pots of spike trains in that paper. I referenced it years ago, on this site, but no-one talked about it after that, so it's buried in the thousands of posts since then (and possibly even lost in the great site crash, who knows?
Please don't "do an SS" on më and use the above as ammunition. You can take it or leave it AFAIAC, but if you leave it, please supply an alternative.

I don't understand what "don't "do an SS" on më and use the above as ammunition." even means, so I doubt I'd do it. I prefer 3/4 inch ball bearings in my black powder 10ga, that I no longer own, for an ammo of choice. I don't even remember what this particular piece of the argument is about and no longer have the reserves of sanity and will to live to continue.

crank wrote:I don't understand what "don't "do an SS" on më and use the above as ammunition." even means, so I doubt I'd do it. I prefer 3/4 inch ball bearings in my black powder 10ga, that I no longer own, for an ammo of choice. I don't even remember what this particular piece of the argument is about and no longer have the reserves of sanity and will to live to continue.

Earlier in this thread (and in others), SS (= Scholastic Spastic) exploited my difficulty in re-locating old references to be, well, just annoying.

On the significance of retinal ganglion spike trains, I see that recent research has complicated the picture somewhat:
PNAS paper: The structure and precision of retinal spike trains

...
All of our visual experience derives from sequences of action potentials traveling down the optic nerve. Many theories have been proposed to explain how these spike trains from retinal ganglion cells encode the visual world (1–4).
...
2. Threshold is defined as the weakest stimulus that can be reliably detected by examination of the output from a retinal ganglion cell; it depends upon (a) the quantum/spike ratio, which is the mean number of additional quantal absorptions required to produce an additional impulse,
...

This is roughly in agreement with my "digitizer" model (taking "impulse" to mean "spike". However other papers conclude that the time delay between the stimulus and the onset of the spike train is more significant, or that the spike rate is more significant than the spike count.

crank wrote:One issue with the idea of neurons firing or not depending on what color you see, this isn't correct. The neurons are firing all the time, their rates go up and down depending on the amount of stimulation a given color receptor in the rods receives. This is important because of the overlap in the spectral sensitivities of the receptors and how this information is processed.

I would also remind again that the color visual system far pre-dates language, humans, and probably mammals. Language really shouldn't enter the discussion about the sensation of color. Doing so makes for a lot of confusion, as we keep seeing.

"Neurons" may be "firing all the time" if you are sloppy about what "all the time" means, and about which neurons you are talking about. I was talking about RGCs (Retinal Ganglion Cells) whose axons feed into the optic nerve. What were you talking about? Pesumably, you were borrowing from GrahamH'earlier post, which said exactly thr same thing, and was therefore just as vague.
I suspect that each cone cell in the fovea has its own RGC, and that the visual cortex (VC) can distinguish the type of each cone cell sending a given signal. Otherwise, how would we see colour at all? (Colour illusions are generated inside the VC, as a kind of post-processing to improve edge visibility, as I described a while back).

DavidMcC wrote:
"Neurons" may be "firing all the time" if you are sloppy about what "all the time" means, and about which neurons you are talking about.

He wasn't being sloppy. His explanation was quite clear.

Sendraks wrote:

DavidMcC wrote:
"Neurons" may be "firing all the time" if you are sloppy about what "all the time" means, and about which neurons you are talking about.

He wasn't being sloppy. His explanation was quite clear.

Look at the paper I linked on the subject of RGC firing. Are they "firing all the time" or not? You have not specitfied what the phrase actually means in terms of the scientific literature, which does not use the phrase.

As I said, Crank's explanation was quite clear.

This digression into particulars of neural activity is of no significance to the topic.

DavidMcC wrote:

crank wrote:One issue with the idea of neurons firing or not depending on what color you see, this isn't correct. The neurons are firing all the time, their rates go up and down depending on the amount of stimulation a given color receptor in the rods receives. This is important because of the overlap in the spectral sensitivities of the receptors and how this information is processed.

I would also remind again that the color visual system far pre-dates language, humans, and probably mammals. Language really shouldn't enter the discussion about the sensation of color. Doing so makes for a lot of confusion, as we keep seeing.

"Neurons" may be "firing all the time" if you are sloppy about what "all the time" means, and about which neurons you are talking about. I was talking about RGCs (Retinal Ganglion Cells) whose axons feed into the optic nerve. What were you talking about? Pesumably, you were borrowing from GrahamH'earlier post, which said exactly thr same thing, and was therefore just as vague.
I suspect that each cone cell in the fovea has its own RGC, and that the visual cortex (VC) can distinguish the type of each cone cell sending a given signal. Otherwise, how would we see colour at all? (Colour illusions are generated inside the VC, as a kind of post-processing to improve edge visibility, as I described a while back).

DavidMcC wrote:On the significance of retinal ganglion spike trains, I see that recent research has complicated the picture somewhat:
PNAS paper: The structure and precision of retinal spike trains

...
All of our visual experience derives from sequences of action potentials traveling down the optic nerve. Many theories have been proposed to explain how these spike trains from retinal ganglion cells encode the visual world (1–4).
...
2. Threshold is defined as the weakest stimulus that can be reliably detected by examination of the output from a retinal ganglion cell; it depends upon (a) the quantum/spike ratio, which is the mean number of additional quantal absorptions required to produce an additional impulse,
...

This is roughly in agreement with my "digitizer" model (taking "impulse" to mean "spike". However other papers conclude that the time delay between the stimulus and the onset of the spike train is more significant, or that the spike rate is more significant than the spike count.

DavidMcC, please note the red stuff, it's the letters that posses the physical color red. In your own words you say it's a rate. And from your link:

As a result, many researchers have concentrated on estimates of the firing rate derived from averages over long time windows or multiple stimulus presentations (9, 10). Measurements of response reliability have often focused on the trial-to-trial variance in this spike count: in the visual cortex, this variance is found to be greater than the mean (11, 12), whereas similar experiments in the thalamus and retina have found variance-to-mean ratios both above and below one (13–15). The picture emerging from this work is that spike trains in the visual system are intrinsically stochastic; that, at best, one can determine the instantaneous probability that the neuron will fire, and that this firing rate depends in some smooth fashion on the sensory stimulus. However, poor reproducibility can also arise from confounding factors (16), such as anesthesia (13), uncontrolled eye movements (17, 18), or ongoing brain activity (19). Furthermore, the response precision may depend on the stimulus. For example, a sudden step change in illumination can reproducibly elicit precisely timed action potentials from retinal ganglion cells (20–22). The importance of precise spike timing has long been appreciated in the auditory system, where it is known to convey information essential for sound localization (23). If high-precision spike trains were common also among visual neurons, their information capacity could be significantly higher than previously estimated (24–26).

The only period where spikes are counted up and read out is part of the testing, so they can average over this period to get the spike rate. There's nothing as far as I know like CCD integrating of spikes and then a dump of the info somehow.

When I said 'neurons' I meant most of them, or at least a bunch of them, that that is a normal way nerves transmit information, it's FM, or really more like Pulse Frequency Modulation. That may be wrong, but it's correct as far as your rods and cones. Remember, I said this rate is important in how you see color, because it isn't that you have bluer>> stronger blue signal, there is a inhibiting factor arising from how much non-blue light is incoming also, this signal slows the firing rate. My fucked up memory isn't up to the task of explaining this very well, but it's something like that.

The ganglion cell thing, not sure exactly what they or you are talking about. I said something about how there is a vast amount of signal processing in the 2 or 3 layers of nerve cells post rods&cones, the data reduction is huge, I think something like 100 or 1000 to one. These layers are ganglion cell layers if I remember correctly, with cell having a shitload of connections to rods and cones and one or a few outputs to next layer of cells, each takes in shitloads of layer1 inputs and one or a few outputs to next layer of cells, and layer3 cells take in a shitload of layer2 outputs and these nerves go into or are the optic nerve cabling into the brain. This is bound to be horribly oversimplified, but then I'm horribly simple. And now I have to go borrow some will to live or I'll be in trouble.

GrahamH wrote:This digression into particulars of neural activity is of no significance to the topic.

Short, to the point and accurate.

GrahamH wrote:This digression into particulars of neural activity is of no significance to the topic

Ha! It was you that started talking about neurons "constantly firing"!
As for the temporary topic of the significance of different aspects of spike trains, I admit I was a bit hasty in choosing the paper I lniked yesterday, because it was about a randomly chosen RGC, which therefore would have been reporting the outputs of a whole 'arbour" of photoreceptors, away from the fovea, instead of the much simpler situation pertaining to the original paper (an RGC connected only to one photoreceptor, in the fovea centralis, and therefore only reporting a cone cell output).

EDIT: The complications of the arbitrarily chosen RGCs would be mainly due to the fact that they have to encode the outputs of many photoreceptors (rods as well as cones) AND encode the positions of each such receptor. This obviously greatly complicates interpretation of the spike trains!

romansh wrote:

GrahamH wrote:This digression into particulars of neural activity is of no significance to the topic.

Short, to the point and accurate.

Yeah, it's easy to be "accurate" when you're not saying anything much.

For Graham's benefit, when there is no l;ight falling on the photoreceptors, most of the RGCs still send light-level/positions-encoded data streams to the lateral geniculate nucleus, so obviously the optic nerves don't go entirely quiet in the dark, even if the photoreceptors themselves do.

crank wrote:...The ganglion cell thing, not sure exactly what they or you are talking about. I said something about how there is a vast amount of signal processing in the 2 or 3 layers of nerve cells post rods&cones, the data reduction is huge, I think something like 100 or 1000 to one. These layers are ganglion cell layers if I remember correctly, with cell having a shitload of connections to rods and cones and one or a few outputs to next layer of cells, each takes in shitloads of layer1 inputs and one or a few outputs to next layer of cells, and layer3 cells take in a shitload of layer2 outputs and these nerves go into or are the optic nerve cabling into the brain. This is bound to be horribly oversimplified, but then I'm horribly simple. And now I have to go borrow some will to live or I'll be in trouble.

FYI, the RGCs transmit the optical data from the retina to the LGN, but they are only connected on a 1-to-1 basis to photoreptors in the fovea centralis, which is only about 0.15 of the retina. Outside that, as I mentioned above, they are connected to a whole arbour of them, to save on optic nerve axons. Thus, the "computations" are mainly only the insertion of receptor position data into the stream, but still the resultant image data is low resolution (and increasingly poor on colour) outside the fovea.

DavidMcC wrote:

GrahamH wrote:This digression into particulars of neural activity is of no significance to the topic

Ha! It was you that started talking about neurons "constantly firing"!

Quote me!