When finally someone asked an expert level, research question these folks got together and closed it. This is very amusing.

Added : (...in view of comments below....)

For a very good example of this type of question and how it was treated on fellow stackexchange site just see here. This should clarify a lot of stuff and this example should be treated as an eye opener.

PS : You don't need to be an expert to ask an expert level question.


As one of the users who voted to close your question, here's my take on it. Despite your claims that it was an expert level or a research question, your actual phrasing of the question leaves a lot to be desired. The question did not make an effort to show that it is a research question that would be of interest to signal processing folks.

In the current question, the phenomenon is most likely due to physiochemical reasons and is not quite related to signal processing. While I agree with several of Pearsonartphoto's points, I disagree with the notion that just because some biological/physical/chemical reaction could also be written in signal processing terms, it makes it right to do so. That might be an interesting approach to perhaps get a point across, but should not substitute for an answer. For example, in a comment to his answer, I say that the transient effects could also be due to an increased relaxation time of the chemicals in the photoreceptors (plausible). Now the math behind my simple argument is merely an exponential decay, which also comes up in radioactive decay, the Arrhenius equation, RC circuits among several others. Does that mean it is reasonable to explain how long it takes Uranium to decay to Thorium using RC circuits? I would think not.

This site should be for specific questions (within the scope) with specific answers. Definitely research level questions that make you think are welcome here. However, we must stay clear of questions that merely state a commonly observed phenomenon and bluntly ask for a signal processing explanation. The onus is upon the OP to do the preliminary research and in fact show beyond reasonable doubt that there indeed is some signal processing involved here. Formulate that in the question and then ask for an explanation.

Lastly, it is highly disingenuous on your part to play the victim when you knew very well that this site was perhaps not the best place to ask this question. From the very first line of your question:

(...I apologize if this question is not apt in here..)


I have a major problem with your question, Rajesh. It's very poorly phrased and stated. There is no signal processing explanation for what you'd like to know, it's all physiochemical. Mathematically, there might be a similarity, but it's a biological non-linear dynamical system you're talking about, and nobody on this site is really expected to know about such things. Mainly, you ask the question like you have no idea of why this happens. If you'd like a grown-up discussion, ask a grown-up question and give us some technical background info so that we could further elaborate on it. For example, which mathematical neuron model are we assuming to use? Do we only include retinal response or interpretive response of the visual cortex, too?

You're asking a very broad question, then downvote everyone's answer and say that you're expecting some cutting edge research level explanation. Just to be objective, you're asking people to give you a PhD thesis paper in return. According to the faq,

Your questions should be reasonably scoped. If you can imagine an entire book that answers your question, you’re asking too much.

Therefore your question was justifiably closed.


In all fairness, the Math.SE OP gave much more context for the question, specified that a soft answer was desired, and the question actually did have a reasonable mathematical explanation. I actually think that there are quite a few very interesting signal processing questions that could be asked in relation to your question, which is why I would encourage you to provide more context/detail.

By way of comparison, most of the interesting signal processing answers to your question would involve some type of mathematical model of some part of the eye. Given that's the case, to test your theory that this community is somehow less welcoming than Math.SE, I'd suggest asking your question verbatim over there, concluded with "I'd appreciate a possible mathematical approach to explain this phenomenon". See what kind of response you get.

If you really do get an overwhelming positive response, that will unquestionably prove your point to everyone here.


I'm on the fence on this one, but here's my arguments.

In Favor:

  1. It turns out that there is a signal processing idea behind the question.
  2. This kind of question could potentially attract experts in processing the signals of biology. Biology is full of signals, most notably in the vision and neural systems, but other things can be models as signals, filters, etc.
  3. While this is related to chemical processes, many chemical processes, especially biological ones, can be modeled as signals. The nature of what composes a signal doesn't matter so much as the fact that there is a signal at the basis of the phenomena. Electrical, chemical, computer, mechanically, hydraulically, thermally, all have methods to obtain a model (Linear or non-linear), which can somehow be processed to produce useful data.


  1. The question as it is currently phrased doesn't seem to have much about signals, but more talks about a phenomena which may or may not be related to signals. Unless the author specifically knew this, they might not have know it.
  2. The wording could be enhanced to explain the desire to get a signal processing method, although I think it is clear upon careful reading that this is the intended result.

After writing this up, I have decided to clear up the wording, and nominate it to be re-opened.


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