We humans have the senses of vision and sound more advanced than other senses, but dogs for example, have highly developed sense of smell.
I've heard a dog can recognize (distinguish) 500 000 of different smells. A normal human being uses less than 80 000 of words in daily communication, and hence the idea of.-- Inyuki, Oct 30 2011 For [zen] http://www.amazon.c...Story/dp/114203416X [MaxwellBuchanan, Oct 31 2011] A Door Is A Man's Best Friend A_20Door_20Is_20a_2...27s_20Best_20Friend [theircompetitor, Oct 31 2011] 500,000 sounds like one of those out-of-the-air figures to me. How could anyone have tested it?
I defy anyone to conceive of a training/testing program which could demonstrate a dog's ability to discriminate 500,000 smells.
Also, how does the dog use this olfactory language? As far as I know, dogs can only produce two odours, and neither of them is under voluntary control.-- MaxwellBuchanan, Oct 30 2011 //out-of-the-air figures// Well, obviously! What other sort of figure would you use to quantify smells?-- mouseposture, Oct 30 2011 Reminder to self - find link to video of Episode 1 (or maybe 2) of Series 1 of Red Dwarf, in which the ship's cat is revealed to have evolved over millions of years into a culture who developed olfactory books deep in the ship's hold.-- zen_tom, Oct 31 2011 Olfactory books were also developed right here on Earth - see link.-- MaxwellBuchanan, Oct 31 2011 Wasn't there a Pratchett novel that discussed the complex olfactory language of an alien race during a sensitive diplomatic mission between humans and the aliens during which the human kept outgassing synthesized insults about them?-- RayfordSteele, Oct 31 2011 //I defy anyone to conceive of a training/testing program // Surely all you need is a multiple choice questionnaire & a pencil?-- DrBob, Oct 31 2011 I'm guessing that dogs can be said to distinguish that many smells in much the way that humans can distinguish a similar number of colours - based on the ability to tell apart closely similar values.
However, it's one thing to be able to tell similar smells apart, but another to be able to recognise that many as individual, absolute values, another another bit of fence to associate those values with concepts, and another another another to deliver them to the dog's olfactory centres with sufficient accuracy and precision (although a tube fed with odorents carefully mixed into a metered air flow, into which the dog places its nose, could do that.)-- spidermother, Oct 31 2011 //I'm guessing that dogs can be said to distinguish that many smells in much the way that humans can distinguish a similar number of colours - based on the ability to tell apart closely similar values.//
Yes, but that doesn't answer the question of how you'd test that ability in a dog. We're talking about 500,000 different smells, and they don't lie on a spectrum (so, you can't say "a dog can distinguish smells that are 0.0002% apart, therefore it can distinguish 500,000 smells").
The only way to know would be to train the dog to give a response if two smells were different. You would then need to test all 500,000 test- substances against each other, for a total of 250,000,000,000 pairwise tests (and that presupposes you know *which* 500,000 smells the dog can distinguish).
250 billion tests, performed at the rate of one per second, would take 7,927 years. That's a good lifespan for any dog.-- MaxwellBuchanan, Oct 31 2011 Exactly - just as for colour discrimination, it's a bit meaningless to present a figure like that without qualifying the methods used, and what is meant by "different smells". However, you should be able to get some sort of order-of-magnitude estimate by using a lot of interpolation and arm-waving (wearing suitable activated carbon armpit pads to prevent confounding smells, of course).
//You would then need to test all 500,000 test- substances against each other, for a total of 250,000,000,000 pairwise tests// [troll] There's this new thing called 'statistics'. You should look into it some time. [/troll]-- spidermother, Oct 31 2011 But, with colour discrimination, you can rely on the fact that colour is a continuum. If you take a simple colour gamut represented in a plane (as an approximation), you can pick, say, 1000 points on that plane and ask how far away from each of the those points a second colour has to be, in order to be discriminable. Thus, you can map colour discrimination fairly accurately and get a reasonably valid answer. (If someone can distinguish two shades of green which are 5 units apart on your gamut; and can distinguish two shades of blue which are 8 units apart; then you can infer reasonably that they can distinguish two shades of turquoise which are 6 or 7 units apart on the same gamut.)
However, I don't see a way to do that for smells, even with arm-waving. Suppose a dog can distinguish peppermint from spearmint, and can distinguish cow's milk from sheep's milk; how do you deduce from that whether it can distinguish a pair of similar smells which are "midway" between milk and mint? There's no gamut of smells, and hence no way to extrapolate, interpolate or intrapolate.
Even if you decided to arrange known smells into some sort of "small gamut", it would be completely human-centric and arbitrary.-- MaxwellBuchanan, Oct 31 2011 Well, colour vision has approximately 4 dimensions (because the rod cells influence the perception of light quality at low levels), so the task is, as you say, relatively simple.
I suppose you would estimate the total number of primary smells available to a dog, then find out how precisely it can distinguish between concentrations of a representative sample of those, and how that precision is affected as the number of primary smells increases. You would have to model the sensitivity curves (I assume they would be logarithmic). The result would still be rather meaningless, though.
I have some experience in this sort of thing. My honours project partly involved studying scent discrimination in mosquitoes, by observing their behaviour. Another research group, meanwhile, was attaching electrodes to mosquito antennas and exposing them to particular molecules, as well as natural scents that were analysed by mass spectrography.-- spidermother, Oct 31 2011 Ah, but what's the number of primary smells? Whereas the three primary colours (plus intensity as per the rods) can be mapped logically to their receptors, the same is not true of odorants mapping to their receptors. One receptor may be activated by many odorants, and one odorant may activate several different receptors. My guess is that there may be on the order of 100 different odorant receptors, and you could argue that 100 different levels of activation could be discriminated for each receptor, giving 100^100 distinguishable smells, which is clearly a lot more than 500,000. Or you could argue that qualitatively different smells would differ in a binary way, giving 2^100 (or about 10^30) different smells - again, a big number (far more than the number of brain cells in a dog, which seldom exceeds 6).
In other words, any estimation based on a realistic number of different receptors and combinatorics gives ludicrous answers.
[EDIT - a quick Google shows that roughly 1000 different canine olfactory receptor genes are known; this makes estimates based on simple combinatorics and reasonable assumptions even more implausible.]
(In contrast, the vision thing works quite plausibly: four receptors, discriminable to within 1%, gives 100^4 colours, which is not many orders of magnitude away from the "millions" which are commonly quoted.)-- MaxwellBuchanan, Oct 31 2011 Yes, we are in agreement - that 500,000 figure is highly dodgy at best.
Obviously, light sensitivity is also roughly logarithmic; we can detect the difference between the light from one candle and two, or a thousand candles and two thousand candles, but not a thousand candles and a thousand and one candles. The same applies to colours and smells.-- spidermother, Oct 31 2011 Agreed.
I'm always curious about "facts" like the 500,000 smells. It's a bit like the folk-fact that the Welsh share 43% of their genome with Neanderthals - potentially true, but on what basis?-- MaxwellBuchanan, Oct 31 2011 random, halfbakery