Wikipedia:Reference desk/Archives/Science/2015 October 30

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October 30

external pressure on blood vessels, blocking blood flow (tourniquet, lying down one position too long etc), sudden release making blood rush to block, shock/zap sensation afterward, want formal medical name of phenomenons

OP curiousMahfuzur rahman shourov (talk) 03:42, 30 October 2015 (UTC)

I think you are looking for the word: Paresthesia. Ariel. (talk) 04:36, 30 October 2015 (UTC)

carbonated beverage cause dehydration real or pseudoscience

OP curiousMahfuzur rahman shourov (talk) 16:32, 30 October 2015 (UTC)

[1] and [2] (may not seem the best source, but it refers albeit doesn't really link to sources like [3]). Carbonated beverage is a fairly unclear term. What applies to carbonated water, may not apply to some carbonated beverage. In particular, I imagine you could carbonate sea water and it could cause dehydration just like sea water could. But I think the evidence like [4] [5] [6] suggest that the majority of carbonated beverages contribute to hydration. That doesn't of course mean they are a great way to achieve hydration, although I think the evidence suggests carbonated water is generally not that much worse than plain water in most respects except that it may be harder to drink a lot of it. I don't know if it makes much sense to call it a pseudoscience, more a myth or superceded claim depending on precisely what you're referring to (e.g. all carbonated beverages, highly caffinated carbonated beverages. Nil Einne (talk) 17:45, 30 October 2015 (UTC)

To the extent that many carbonated beverages have caffeine in them, this is often true, caffeine being a diuretic. Snow ^{let's rap} 19:38, 30 October 2015 (UTC)

Yes, but it's only short-term stimulation of urine output, and only occurs when people haven't had caffeine for days or weeks. Conclusion was: Doses of caffeine equivalent to the amount normally found in standard servings of tea, coffee and carbonated soft drinks appear to have no diuretic action.. And when "severe" dehydration is considered, you'll always be better off drinking than not drinking. Ssscienccce (talk) 21:20, 30 October 2015 (UTC)

Well, I can't say as I didn't realize that tea and coffee (being almost entirely water) result in net hydration, but I was previously unfamiliar with that review and am surprised that the diuretic effect in doses of the sizes discussed is so limited; thanks for the source and the fix to discussion! Snow ^{let's rap} 01:06, 31 October 2015 (UTC)

Caffeine has little or no impact on hydration [7][8]. Mikenorton (talk) 21:23, 30 October 2015 (UTC)

Caffeine does increase urine output, which can have a secondary effect on hydration: Caffeine#Physical. --Jayron32 18:44, 31 October 2015 (UTC)

30-40 years ago Coca Cola had lots of caffeine and salt, presumably to make people buy even more Cola. But things have changed since then, e.g. I routinely drink Cola Zero and I have noticed no dehydration effect. Tgeorgescu (talk) 17:10, 31 October 2015 (UTC)

Did it? I'm not an expert Cokeologist, but I think the formula has remained basically the same for many decades, excepting the switch in the U.S. from cane sugar to HFCS, and the well-known and brief introduction of New Coke. "Coke [or other colas] has lots of caffeine and salt to make you thirsty" is something I hear occasionally, but it appears to not really be true. A can of Coca-Cola has 45 mg of sodium and 34 mg of caffeine, which is barely any. Coke Zero has 5 mg less of sodium, an insignificant difference. Compare to a cup of coffee, which tends to run around 100-200 mg of caffeine, depending on a lot of variables (see the caffeine article for a table of caffeine content). And as mentioned above and in the article, if you consume caffeine regularly you rapidly develop tolerance to its diuretic effect, which is fairly mild to begin with. On the other hand, alcoholic beverages can dehydrate you, because ethanol interferes with antidiuretic hormone, increasing urine output, and this effect seems to be less susceptible to tolerance. Dehydration is thought to be one of the factors that contribute to hangovers. --71.119.131.184 (talk) 00:22, 1 November 2015 (UTC)

7 Up evidentally used to have a higher sodium content, although since we're talking about hydration, I'm not sure if things have changed much since they changed that by switchign to potassium citrate. Very long ago, Coca-Cola was obviously different [9] but I agree, I'm not convinced it ever had a much higher sodium content in recent decades. Amongst other things, I'm fairly sure the taste would be fairly different if the sodium content was significantly higher.

And as you said, caffeine seems largely irrelevant, the evidence both from the sources I've presented in my first post, and others suggests it doesn't result in coffee being dehydrating let alone Coke. Admitedly having taken a more careful read of the sources (well the ones I provided, didn't check the other ones), I'm not certain there's no effect in people who hardly ever take caffeine, however even so it seems unlikely the effect is much in Coke, at most it may be least hydrating than expected rather than being dehydrating.

Nil Einne (talk) 18:12, 1 November 2015 (UTC)

Most carbonated beverages are caffinated products such as pepsi or mountain dew. Caffeine is a natural diuretic when consumed by a individual. The action that the caffeine diuretic has on the body is the urge for the individual to urinate. If a individual is constantly urinating this can cause a shift in fluid balance causing the individual to become dehydrated along with various electrolyte imbalances due to excessive urinating. goes into more detail about the effects that diuretics can have on an individual. However as stated on the Mayo Clinic web page states that carbonated drinks do not have enough of a diuretic affect to cause dehydration alone. However if that is all you are drinking, your not eating well, and not consuming enough water you can experience dehydration. This is not solely because of the consumption of the carbonated drinks it is due to not enough water consumption.

If you are someone who drinks carbonated drinks all day everyday it will increase you sodium level which can cause dehydration because water follows sodium. Therefore with increase sodium excretion you will be excreting more water causing dehydration. However if you are consuming adequate water and only drink these carbonated drinks occasionally you will most likely not experience dehydration. Kendra ann (talk) 00:34, 3 November 2015 (UTC)

Do dogs really smell fear?

Do dogs (and animals at all) smell fear? Does the fear has "fear molecules" that spread in the air? 21:17, 30 October 2015 (UTC) — Preceding unsigned comment added by 78.111.186.78 (talk)

I don't know - but dogs are renowned for being extremely sensitive to human body language - and my suspicion is that this is what they are really reacting to. That said, we probably do give off enough chemicals of one sort or another that the dog could also be detecting that. It's hard to say which! SteveBaker (talk) 21:35, 30 October 2015 (UTC)

Dogs are social animals. The negociate their rank with the human inside the pack. They sense what some civil education had stolen the people. --Hans Haase (有问题吗) 22:01, 30 October 2015 (UTC)

Cortisol is a likely culprit; even humans seem to be able to smell fear in other humans, according to this study [10]. Dogs can do all sorts of things. Here's a case study of a dog detecting low blood sugar in a human [11], and Seizure_response_dog has some interesting refs on some dogs being able to predict seizures in humans. As Steve says, lots of other cues aside from smell probably come in to play as well. SemanticMantis (talk) 22:18, 30 October 2015 (UTC)

If a human can smell your fear, it's time to change your underpants. StuRat (talk) 00:31, 1 November 2015 (UTC)

(edit conflict) I found plenty of "popular" articles to back up SteveBaker's suggestion - a mixture of human scent changes caused by stress and body language. See this or this for example. Alansplodge (talk) 22:20, 30 October 2015 (UTC)

Well I would be surprised if anyone had done any detailed research in this area (meaning specific to dogs and the specific mechanism by which they might perceive fear in humans. Those reports of "disease-sniffing" dogs garner some attention because they strike us as so phenomenal, but the truth is a case study here and there doesn't tell us much about what is really going on (if indeed anything other than the human tendency to see a pattern where there is none and to ascribe superhuman (supercanine?) abilities of acuity, affinity, and intuition to our animal companions. Meaning no offense to SM, undoubtedly one of our all time best scientific reference contributors here, but that particular source is pretty representative of the kind of questionable "science" that goes into these inquiries. It takes as rather for granted a phenomena that is highly questionable and can probably be explained a hundred different ways that are more likely than those being presented, to say nothing of the sample size of one and the kind of subjective "evidence" being presented (the survey it cites doesn't not sound anymore empirically valid). And then there's this gem at the end: "One other possibility may be the dogs’ detection, of energy wave changes in a person’s electrical and/or magnetic fields during a hypoglycaemic episode. This is as yet undetermined." Yeah....

Anyway, I've limited knowledge of the research surrounding dog olfaction, but I am an expert in perception broadly, with a sharp interest in it's relevance sociobiology and my instinct is that Steve probably has hit on the more likely explanation. Certainly I am generally loathe to provide speculation in place of a good source in this space, but that's my best insight anyway. Certainly we know for a fact that dogs are immensely responsive to body language -- that's an area of much more robust understanding, with regard to both intuitive observation and research. I wouldn't entirely discount the possibility of sensitivity to olfactory stimulus in this area, given the breadth of chemoreception in dogs with regard to smell, but I'd expect it to play a secondary role. In animals with decent vision and no major omnipresent predators in their ecological niche, vision almost always takes the central role in threat response, especially in particularly social species. Snow ^{let's rap} 01:40, 31 October 2015 (UTC)

Snow, I think you might have been just a little premature dismissing the low-blood sugar example. Please see Rooney, N. J., Morant, S., & Guest, C. (2013). Investigation into the value of trained glycaemia alert dogs to clients with type I diabetes. PloS one, 8(8), 1-12. [12]

People may also wish to read Cornu, J. N., Cancel-Tassin, G., Ondet, V., Girardet, C., & Cussenot, O. (2011). Olfactory detection of prostate cancer by dogs sniffing urine: a step forward in early diagnosis. European urology, 59(2), 197-201[13]DrChrissy ^(talk) 02:02, 31 October 2015 (UTC)

Perhaps I put my thoughts inartfully; my doubts are more focused on the role of olfaction in the scenario presented above than in the possibility that a pet canine may detect declining health or even be sensitive to a specific kind of physiological imbalance in someone they are familiar with. Mind you, even with regard to the later, those studies present pretty mediocre confirmation (small sample sizes, little to no control, lack of firm understanding for the mechanisms involved, and a whole host of other issues which limit the observations we can make here. But all of that said, I don't doubt that dogs pick up on changes of the well being in their companions; I just find the research in the specifics a little underwhelming at this stage. Note also that there are two different kinds of phenomena being discussed here: A) undirected (and often socially influenced) perception of a vague change, 1) by the canine, 2) as to the physiology of the human, and often observed to some extent by the human, who often is the subject of the experience, close to the other subject (the dog) and often is not someone of scientific background, and B) a trained response to a specific stimuli. I don't doubt in the least that a dog can be trained to sniff out a stimulus that is predictive of cancer in urine; that's completely non-controversial and unsurprising to me, as dogs can be trained to detect a wide range of olfactory stimuli. But that's an entirely different matter from saying "My king charles spaniel is a living glucometer, who can smell my blood sugar and read my magnetic aura!" Snow ^{let's rap} 02:27, 31 October 2015 (UTC)

Snow, you appear to be lumping all studies in this area into one basket and saying they are all rubbish. The first one presented has "case study" in the title so we are all fore-warned about the potential for a lack of extrapolation. However, the two other studies I put forward are considerably more robust and don't even mention magnetic aura! Are you saying that your criticisms above apply to these two studies?DrChrissy ^(talk) 20:38, 31 October 2015 (UTC)

Well I'm not presuming all possible studies in this area will suffer from the above shortcomings, and certainly the spaniel comment at the end of my post was directed at the case study, but if pushed to give an evaluation of the empirical rigor of the other papers, then my impression is not really all that much better. Let's take the PLOS One study. It has a small sample size, it relies on self-reporting by the subjects, it proposes no mechanism for how the dogs supposedly perceive the low blood sugar, it omits any discussion whatsoever of the methodology by which the dogs were "trained", its statistical results are pretty mediocre, and it has pretty much zero control along, oh about a bazillion factors that could skew the results here.

All observations were conducted by lay people and most of the dogs were owned by the subjects prior to their training for this task. That they had an (ever so slight) uptake in how often they caught their unabalanced blood sugars (which, despite some red herrings in the way the study is written, is the only statistical assertion it claims to make) after their pets were trained (or they received the new pet) could mean just about anything. The fact that they now believe that they have a glucose-detecting wonder dog could cause them to check more frequently. And whatever the training regimen was like, it could not have been too demanding and particular, looking at how the dogs "alerted" their owners: "stare, paw, and sometimes grunts"; "yawn, tap me, and stay with me"; "agitated then stares"; squaek and stay with me, if other person is present alerts them though not trained to" [emphasis added]; "jumps up, licks, sits next to". On top of all of this ambiguity, those conducting the experiment apparently encouraged the (human) participants to reward their dogs for alerting them. I need hardly tell any scientist (or indeed any person who has ever had a dog) how this might confuse the results. Even the a authors, when trying to account for the statistical variations that would otherwise complicate their conclusions, concede the problems here (but then proceed to dismiss this glaring issue under a pretty laughable assumption: "Since the data is owner-reported, it is also possible that a belief in their dogs’ ability led some owners, consciously or inadvertently, to be more likely to record ambiguous behaviours as alerts only when their sugars were subsequently found to be low, as compared to normal, or to conduct routine tests, when they were likely to be in within target range. However clients were made aware that records were also to be used to detect training issues and to direct remedial training, so we believe this risk was mitigated and it is extremely unlikely that all clients were biased."

And I've barely scratched the surface on the likely conflating factors, lackluster methodology, and ambiguous results here. I could easily go all day discussing why the conclusions reached are dubious. So yes, while I was trying not to be so strident on the matter, since you've put me in the hot seat, I find this to be a very weak study, full of issues and devoid of much compelling empirical value. But let's assume, just for the sake of bringing discussion back around to the main issue of this thread, that we accept that the dogs are perceiving when the blood sugars of their human companions have entered into a dangerous range. That still would not mean they were smelling it. It might be any of a huge range of changes in the condition of their owner that they were responding to.

As to the study on dogs sniffing for stimulants indicative of cancer in urine, I have not really reviewed it, but as I said before, I've little doubt that this can be accomplished and, in any event, that kind of study can be conducted in a much more straight-forward and controlled fashion. In fact, though I don't recall the specifics, I've seen research in this area before and don't remember coming away with a bad impression of the methodology. Snow ^{let's rap} 00:30, 1 November 2015 (UTC)

Thanks for this. The first study is one of "Applied behaviour science". I am not for one second saying this discipline should be allowed to produce sub-standard science, however, it should sometimes be treated a little differently from an extreme reductionist-type study. For example, the mechanism of detection by the dogs may not need to be understood in this preliminary work, but the reductionist approach to determining the exact mechanism would be a valuable area of future research. Similarly, the number of dogs used (10 for which all records were available) is perfectly representative of studies such as this, supported by the finding that 8 of the dogs were shown to behave predictably.DrChrissy ^(talk) 14:09, 2 November 2015 (UTC)

I'm afraid I strongly disagree with some of those points. Regardless of variance in standards, a study's persuasiveness is directly linked to the empirical rigor of it's methodology and analysis of its data. Here, the structure of the study is lacking in control in many crucial areas and the willingness of the authors to dismiss important conflating factors, together with some questionable statistical interpretations, just seem to me highly suggestive of a confirmation bias, wherever they were reporting and whoever their audience. We can, in the case of this study, put aside the issue of a specific sensory mechanism and concentrate just on behavioural observation the study claims to (sort of) validate, but there I strongly disagree with the conclusion that it demonstrated that "the finding that 8 of the dogs were shown to behave predictably", by any stretch of what I would consider reasonable evidenciary standards. But again, this not an opinion I would have volunteered--this is well outside the normal (and hopefully objective) purposes to which I try to apply myself on the ref desks--except for the fact that I was specifically asked to give it.

On a more general note, though, I would disagree that a sample size of 10 subjects is really a convincing standard in any area of behavioural science, applied or otherwise. Also, it says something when you have to reduce your original pool of participants by half because your methods returned data that was too incomplete or confused to be of use for the omitted participants, though clearly that is unavoidable when you use self-report questionnaires. But anyway, I fear we've strayed a bit from direct relevance to the question of the OP (who, in any event, does not seem to engage with his questions after they are asked), so perhaps we should leave it there lest I have to provide more critiques of the work of other researchers, which I'd rather avoid as much as possible in this particular space. Snow ^{let's rap} 06:09, 3 November 2015 (UTC)

A sample size of 10 is very often used in animal behaviour studies, especially those where the animal is used as it's own control. There are even case-studies involving just (shock! horror!) one individual, take Clever hans (obviously debunked), Koko (gorilla) and Alex (parrot). I'm sorry you do not like providing critiques of papers - but surely if you criticize a paper, you would expect to provide details supporting your criticisms.DrChrissy ^(talk) 18:44, 3 November 2015 (UTC)

You've chosen three of the most notorious examples of cases where the scientific community has questioned the empirical validity of expansive claims about animal communication by those closest to the research and subject, so you seem to rather undermining your own point. Regardless, you can assert all you like that ten subjects is a typical standard for "animal behaviour studies" (a rather broad term), but you'll have to be more clear where you're arriving at that number/conclusion. Clearly there is some room for context and for the nature of the claims being asserted, but I can't imagine many complex studies where 10 would be considered a very robust number for peer-review research. Certainly in this case, with the assertion being made, it's very underwhelming, especially when put together with the shortcoming in the methodology. Likewise, it's a bit vague what you mean by saying "the dogs are their own control" in this context, since the study is not testing for "dog" (whatever that would mean), but none of the likely possibilities of interpretation as to your meaning here that occur to me are likely to make that statement correct, since this study has control issues all over the place with regard to the dog, the people, and the instrumentality of the record taking. There's a reason why very little serious scientific research does not make the subject responsible for making the observations and recording the data.

This seems to me a case of the aims of the researchers vastly exceeding their practical means. You could do this study in a much more clinical fashion, with an independent observer and much more control, but they obviously didn't have the resources to conduct that experiment, and they proceeded anyway. When you do that you're already setting out on the wrong foot and you ought to be immensely careful about your statistical analysis and (even with rigorous analysis) be very careful about what conclusions you draw, especially in the vein of behaviour. The present authors instead just barely acknowledge a handful of the issues in control and interpretation in the way they wrote the paper and then proceed to dismiss these very serious shortcomings with (frankly glib) explanations which don't stand up to even minimal scrutiny when you consider the claims they are making. "We just don't think they would be subject to the normal errors in reporting bias of an involved subject with only lay knowledge because we told them it was really really important." just does not cut it in real research of this nature, I am afraid.

To be fair, even if you had all the money and resources int he world, and access to the highest quality clinical environment, this would, at present level of technology and understanding of the underlying issues, be an almost impossible experiment to control for, just by virtue of what they are trying to prove. But even within that framework this is an unimpressive study. Notice too that the authors kind of allude to these facts and reference another study along the same lines by one of the authors which did attempt to use an independent observer; they note (improperly in my opinion, since they give no real details about the study) that the data in that case was convergent with what they found here, but that the study is unpublished. Which raises the question, why not publish the methodologically sound study instead of this problematic one? I have some good guesses which I won't go into, but regardless it's just another open question that highlights the issues here.

And I actually didn't start out by critiquing the study; I was speaking rather more broadly on the topic of studies in this area of olfaction. You asked me to distinguish whether my view was consistent with the sources you provided and I've elucidated as best I can. Clearly we have two different standards here and you think mine is overly-heavy, even unreasonable, but I'm afraid I just don't see it that way; I think accomplished researchers working even outside the area of perception and behaviour broadly would see the statistical and methodological issues in that study right away. Snow ^{let's rap} 21:56, 3 November 2015 (UTC)

I think you are misrepresenting me slightly. I did not say N=10 is a standard in animal behaviour studies. I said it is "often used" in animal behaviour studies. In fact, I should have been more specific about this and said a low N is often used; I am not claiming anything magical about N=10. There are many animal behaviour studies where N<10 This is often because of ethical considerations or economic considerations (have you any idea how expensive it is to keep an experimental pig for several weeks!). I will not provide examples of N<10 as it would be way too easy for me to present biased results. Instead, I suggest you conduct a search of "cognition in XXXX" and enter your favourite farm or zoo animal. I will be surprised if you find many studies with N>10. This includes many studies on cognitive capabilities such as theory of mind, deception, tool-use, etc. By the way, I was not suggesting the dogs were being used as their own controls in the Rooney study - I was thinking of other studies where this approach is used in behavioural studies to increase the power of the study.DrChrissy ^(talk) 00:07, 4 November 2015 (UTC)

Then perhaps we are more in agreement than I might have thought. I'd only add that, whatever cost-saving measures might cause a researcher to restrict their sample size, that doesn't alleviate their results from being less empirically persuasive as a result of that limitation. And the conclusions must always be examined in light of the evidence. So whatever one might argue is "common" or "necessary" to a particular vein of research does not really influence the objective strengths (or weaknesses) of a study's conclusions, which is the only issue I was speaking to from the outset. You can take the best evidence your fellow researchers have previously provided and use that as a starting point for your own assumptions, but you can't evaluate the claims of a given study on a curve. It's methodology and empirical weight, in this sense, must be evaluated in isolation, or else it does not truly conform to the scientific process. Snow ^{let's rap} 00:47, 4 November 2015 (UTC)

We are in agreement! Thank-you for the interesting discussion.DrChrissy ^(talk) 15:34, 4 November 2015 (UTC)

Meh, It's no offense to me that a case study is not grounds for scientific, mechanistic understanding, that's why I clearly called it that. What do you think about the humans smelling fear in humans article? I just skimmed it, but the discussion seemed very adamant that cortisol was both involved but also not the only factor. I was thinking that if we have good evidence that some humans can sense some human fear via olfaction, then it doesn't stretchy my credulity to think that dogs can too. After all, they generally have olfactory detection far superior to ours, cortisol and similar compounds are used similarly and widely throughout mammalia, and we've been selectively breeding dogs that can better understand us for a very long time ;) SemanticMantis (talk) 16:41, 31 October 2015 (UTC)

Me too. the point I was making above was that if a dog can be trained to indicate the odour of something, it can obviously smell it. I think the case of smelling cancer may in fact be far more surprising than SNOW predicts to people less widely read than SNOW. Don't forget, the OP question was "Do dogs smell fear". My gut-reaction would be that I think it is likely, but, I would want to see some robust evidence for it before making a definitive statement. Speaking of case studies, a woman's apparent ability to smell Parkinson's hit the news this week in the UK.[14] A case-study, yes, but it does start us thinking.DrChrissy ^(talk) 16:51, 31 October 2015 (UTC)